mm: shmem_zero_setup skip security check and lockdep conflict with XFS

mm: shmem_zero_setup skip security check and lockdep conflict with XFS

[Hugh Dickins]

It appears that, at some point last year, XFS made directory handling
changes which bring it into lockdep conflict with shmem_zero_setup():
it is surprising that mmap() can clone an inode while holding mmap_sem,
but that has been so for many years.

Since those few lockdep traces that I've seen all implicated selinux,
I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
v3.13's commit c7277090927a ("security: shmem: implement kernel private
shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.

This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
(and MAP_SHARED|MAP_ANONYMOUS).  I thought there were also drivers
which cloned inode in mmap(), but if so, I cannot locate them now.

Reported-and-tested-by: Prarit Bhargava <prarit@redhat.com>
Reported-by: Daniel Wagner <wagi@monom.org>
Reported-by: Morten Stevens <mstevens@fedoraproject.org>
Signed-off-by: Hugh Dickins <hughd@google.com>
---

 mm/shmem.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- 4.1-rc7/mm/shmem.c	2015-04-26 19:16:31.352191298 -0700
+++ linux/mm/shmem.c	2015-06-14 09:26:49.461120166 -0700
@@ -3401,7 +3401,13 @@ int shmem_zero_setup(struct vm_area_stru
 	struct file *file;
 	loff_t size = vma->vm_end - vma->vm_start;
 
-	file = shmem_file_setup("dev/zero", size, vma->vm_flags);
+	/*
+	 * Cloning a new file under mmap_sem leads to a lock ordering conflict
+	 * between XFS directory reading and selinux: since this file is only
+	 * accessible to the user through its mapping, use S_PRIVATE flag to
+	 * bypass file security, in the same way as shmem_kernel_file_setup().
+	 */
+	file = __shmem_file_setup("dev/zero", size, vma->vm_flags, S_PRIVATE);
 	if (IS_ERR(file))
 		return PTR_ERR(file);
 

Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS

[Daniel Wagner]

On 06/14/2015 06:48 PM, Hugh Dickins wrote:
> It appears that, at some point last year, XFS made directory handling
> changes which bring it into lockdep conflict with shmem_zero_setup():
> it is surprising that mmap() can clone an inode while holding mmap_sem,
> but that has been so for many years.
> 
> Since those few lockdep traces that I've seen all implicated selinux,
> I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
> v3.13's commit c7277090927a ("security: shmem: implement kernel private
> shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
> the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.
> 
> This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
> (and MAP_SHARED|MAP_ANONYMOUS).  I thought there were also drivers
> which cloned inode in mmap(), but if so, I cannot locate them now.
> 
> Reported-and-tested-by: Prarit Bhargava <prarit@redhat.com>
> Reported-by: Daniel Wagner <wagi@monom.org>

Reported-and-tested-by: Daniel Wagner <wagi@monom.org>

Sorry for the long delay. It took me a while to figure out my original
setup. I could verify that this patch made the lockdep message go away
on 4.0-rc6 and also on 4.1-rc8.

For the record: SELinux needs to be enabled triggering it.

cheers,
daniel

Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS

[Hugh Dickins]

On Mon, 15 Jun 2015, Daniel Wagner wrote:
> On 06/14/2015 06:48 PM, Hugh Dickins wrote:
> > It appears that, at some point last year, XFS made directory handling
> > changes which bring it into lockdep conflict with shmem_zero_setup():
> > it is surprising that mmap() can clone an inode while holding mmap_sem,
> > but that has been so for many years.
> > 
> > Since those few lockdep traces that I've seen all implicated selinux,
> > I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
> > v3.13's commit c7277090927a ("security: shmem: implement kernel private
> > shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
> > the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.
> > 
> > This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
> > (and MAP_SHARED|MAP_ANONYMOUS).  I thought there were also drivers
> > which cloned inode in mmap(), but if so, I cannot locate them now.
> > 
> > Reported-and-tested-by: Prarit Bhargava <prarit@redhat.com>
> > Reported-by: Daniel Wagner <wagi@monom.org>
> 
> Reported-and-tested-by: Daniel Wagner <wagi@monom.org>

Great, thank you Daniel: we look more convincing now :)

> 
> Sorry for the long delay. It took me a while to figure out my original
> setup. I could verify that this patch made the lockdep message go away
> on 4.0-rc6 and also on 4.1-rc8.

Thank you for taking the trouble.

> 
> For the record: SELinux needs to be enabled triggering it.

Right, selinux was in all the stacktraces we saw, and I was banking
on that security "recursion" being what actually upset lockdep; but
couldn't be sure until you tried it out.

We didn't make -rc8, and I won't be at all surprised if Linus feels
that a year(?)-old lockdep warning is not worth disturbing v4.1
final for, but it should get into v4.2 (thank you, Andrew).

Hugh

Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS

[Morten Stevens]

2015-06-15 8:09 GMT+02:00 Daniel Wagner <wagi@monom.org>:
> On 06/14/2015 06:48 PM, Hugh Dickins wrote:
>> It appears that, at some point last year, XFS made directory handling
>> changes which bring it into lockdep conflict with shmem_zero_setup():
>> it is surprising that mmap() can clone an inode while holding mmap_sem,
>> but that has been so for many years.
>>
>> Since those few lockdep traces that I've seen all implicated selinux,
>> I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
>> v3.13's commit c7277090927a ("security: shmem: implement kernel private
>> shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
>> the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.
>>
>> This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
>> (and MAP_SHARED|MAP_ANONYMOUS).  I thought there were also drivers
>> which cloned inode in mmap(), but if so, I cannot locate them now.
>>
>> Reported-and-tested-by: Prarit Bhargava <prarit@redhat.com>
>> Reported-by: Daniel Wagner <wagi@monom.org>
>
> Reported-and-tested-by: Daniel Wagner <wagi@monom.org>
>
> Sorry for the long delay. It took me a while to figure out my original
> setup. I could verify that this patch made the lockdep message go away
> on 4.0-rc6 and also on 4.1-rc8.

Yes, it's also fixed for me after applying this patch to 4.1-rc8.

Best regards,

Morten

Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS

[Hugh Dickins]

 Wed, Jun 17, 2015 at 12:45 PM, Morten Stevens
<mstevens@fedoraproject.org> wrote:
> 2015-06-15 8:09 GMT+02:00 Daniel Wagner <wagi@monom.org>:
>> On 06/14/2015 06:48 PM, Hugh Dickins wrote:
>>> It appears that, at some point last year, XFS made directory handling
>>> changes which bring it into lockdep conflict with shmem_zero_setup():
>>> it is surprising that mmap() can clone an inode while holding mmap_sem,
>>> but that has been so for many years.
>>>
>>> Since those few lockdep traces that I've seen all implicated selinux,
>>> I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
>>> v3.13's commit c7277090927a ("security: shmem: implement kernel private
>>> shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
>>> the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.
>>>
>>> This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
>>> (and MAP_SHARED|MAP_ANONYMOUS).  I thought there were also drivers
>>> which cloned inode in mmap(), but if so, I cannot locate them now.
>>>
>>> Reported-and-tested-by: Prarit Bhargava <prarit@redhat.com>
>>> Reported-by: Daniel Wagner <wagi@monom.org>
>>
>> Reported-and-tested-by: Daniel Wagner <wagi@monom.org>
>>
>> Sorry for the long delay. It took me a while to figure out my original
>> setup. I could verify that this patch made the lockdep message go away
>> on 4.0-rc6 and also on 4.1-rc8.
>
> Yes, it's also fixed for me after applying this patch to 4.1-rc8.

Thank you - Hugh

>
> Best regards,
>
> Morten

Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS

[Stephen Smalley]

On Sun, Jun 14, 2015 at 12:48 PM, Hugh Dickins <hughd@google.com> wrote:
> It appears that, at some point last year, XFS made directory handling
> changes which bring it into lockdep conflict with shmem_zero_setup():
> it is surprising that mmap() can clone an inode while holding mmap_sem,
> but that has been so for many years.
>
> Since those few lockdep traces that I've seen all implicated selinux,
> I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
> v3.13's commit c7277090927a ("security: shmem: implement kernel private
> shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
> the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.
>
> This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
> (and MAP_SHARED|MAP_ANONYMOUS).  I thought there were also drivers
> which cloned inode in mmap(), but if so, I cannot locate them now.

This causes a regression for SELinux (please, in the future, cc
selinux list and Paul Moore on SELinux-related changes).  In
particular, this change disables SELinux checking of mprotect
PROT_EXEC on shared anonymous mappings, so we lose the ability to
control executable mappings.  That said, we are only getting that
check today as a side effect of our file execute check on the tmpfs
inode, whereas it would be better (and more consistent with the
mmap-time checks) to apply an execmem check in that case, in which
case we wouldn't care about the inode-based check.  However, I am
unclear on how to correctly detect that situation from
selinux_file_mprotect() -> file_map_prot_check(), because we do have a
non-NULL vma->vm_file so we treat it as a file execute check.  In
contrast, if directly creating an anonymous shared mapping with
PROT_EXEC via mmap(...PROT_EXEC...),  selinux_mmap_file is called with
a NULL file and therefore we end up applying an execmem check.

>
> Reported-and-tested-by: Prarit Bhargava <prarit@redhat.com>
> Reported-by: Daniel Wagner <wagi@monom.org>
> Reported-by: Morten Stevens <mstevens@fedoraproject.org>
> Signed-off-by: Hugh Dickins <hughd@google.com>
> ---
>
>  mm/shmem.c |    8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> --- 4.1-rc7/mm/shmem.c  2015-04-26 19:16:31.352191298 -0700
> +++ linux/mm/shmem.c    2015-06-14 09:26:49.461120166 -0700
> @@ -3401,7 +3401,13 @@ int shmem_zero_setup(struct vm_area_stru
>         struct file *file;
>         loff_t size = vma->vm_end - vma->vm_start;
>
> -       file = shmem_file_setup("dev/zero", size, vma->vm_flags);
> +       /*
> +        * Cloning a new file under mmap_sem leads to a lock ordering conflict
> +        * between XFS directory reading and selinux: since this file is only
> +        * accessible to the user through its mapping, use S_PRIVATE flag to
> +        * bypass file security, in the same way as shmem_kernel_file_setup().
> +        */
> +       file = __shmem_file_setup("dev/zero", size, vma->vm_flags, S_PRIVATE);
>         if (IS_ERR(file))
>                 return PTR_ERR(file);
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS

[Stephen Smalley]

On 07/08/2015 09:13 AM, Stephen Smalley wrote:
> On Sun, Jun 14, 2015 at 12:48 PM, Hugh Dickins <hughd@google.com> wrote:
>> It appears that, at some point last year, XFS made directory handling
>> changes which bring it into lockdep conflict with shmem_zero_setup():
>> it is surprising that mmap() can clone an inode while holding mmap_sem,
>> but that has been so for many years.
>>
>> Since those few lockdep traces that I've seen all implicated selinux,
>> I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
>> v3.13's commit c7277090927a ("security: shmem: implement kernel private
>> shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
>> the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.
>>
>> This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
>> (and MAP_SHARED|MAP_ANONYMOUS).  I thought there were also drivers
>> which cloned inode in mmap(), but if so, I cannot locate them now.
> 
> This causes a regression for SELinux (please, in the future, cc
> selinux list and Paul Moore on SELinux-related changes).  In
> particular, this change disables SELinux checking of mprotect
> PROT_EXEC on shared anonymous mappings, so we lose the ability to
> control executable mappings.  That said, we are only getting that
> check today as a side effect of our file execute check on the tmpfs
> inode, whereas it would be better (and more consistent with the
> mmap-time checks) to apply an execmem check in that case, in which
> case we wouldn't care about the inode-based check.  However, I am
> unclear on how to correctly detect that situation from
> selinux_file_mprotect() -> file_map_prot_check(), because we do have a
> non-NULL vma->vm_file so we treat it as a file execute check.  In
> contrast, if directly creating an anonymous shared mapping with
> PROT_EXEC via mmap(...PROT_EXEC...),  selinux_mmap_file is called with
> a NULL file and therefore we end up applying an execmem check.

Also, can you provide the lockdep traces that motivated this change?

> 
>>
>> Reported-and-tested-by: Prarit Bhargava <prarit@redhat.com>
>> Reported-by: Daniel Wagner <wagi@monom.org>
>> Reported-by: Morten Stevens <mstevens@fedoraproject.org>
>> Signed-off-by: Hugh Dickins <hughd@google.com>
>> ---
>>
>>  mm/shmem.c |    8 +++++++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> --- 4.1-rc7/mm/shmem.c  2015-04-26 19:16:31.352191298 -0700
>> +++ linux/mm/shmem.c    2015-06-14 09:26:49.461120166 -0700
>> @@ -3401,7 +3401,13 @@ int shmem_zero_setup(struct vm_area_stru
>>         struct file *file;
>>         loff_t size = vma->vm_end - vma->vm_start;
>>
>> -       file = shmem_file_setup("dev/zero", size, vma->vm_flags);
>> +       /*
>> +        * Cloning a new file under mmap_sem leads to a lock ordering conflict
>> +        * between XFS directory reading and selinux: since this file is only
>> +        * accessible to the user through its mapping, use S_PRIVATE flag to
>> +        * bypass file security, in the same way as shmem_kernel_file_setup().
>> +        */
>> +       file = __shmem_file_setup("dev/zero", size, vma->vm_flags, S_PRIVATE);
>>         if (IS_ERR(file))
>>                 return PTR_ERR(file);
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>> Please read the FAQ at  http://www.tux.org/lkml/
> _______________________________________________
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> To get help, send an email containing "help" to Selinux-request@tycho.nsa.gov.
> 
> 

Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS

[Morten Stevens]

2015-07-08 18:37 GMT+02:00 Stephen Smalley <sds@tycho.nsa.gov>:
> On 07/08/2015 09:13 AM, Stephen Smalley wrote:
>> On Sun, Jun 14, 2015 at 12:48 PM, Hugh Dickins <hughd@google.com> wrote:
>>> It appears that, at some point last year, XFS made directory handling
>>> changes which bring it into lockdep conflict with shmem_zero_setup():
>>> it is surprising that mmap() can clone an inode while holding mmap_sem,
>>> but that has been so for many years.
>>>
>>> Since those few lockdep traces that I've seen all implicated selinux,
>>> I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
>>> v3.13's commit c7277090927a ("security: shmem: implement kernel private
>>> shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
>>> the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.
>>>
>>> This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
>>> (and MAP_SHARED|MAP_ANONYMOUS).  I thought there were also drivers
>>> which cloned inode in mmap(), but if so, I cannot locate them now.
>>
>> This causes a regression for SELinux (please, in the future, cc
>> selinux list and Paul Moore on SELinux-related changes).  In
>> particular, this change disables SELinux checking of mprotect
>> PROT_EXEC on shared anonymous mappings, so we lose the ability to
>> control executable mappings.  That said, we are only getting that
>> check today as a side effect of our file execute check on the tmpfs
>> inode, whereas it would be better (and more consistent with the
>> mmap-time checks) to apply an execmem check in that case, in which
>> case we wouldn't care about the inode-based check.  However, I am
>> unclear on how to correctly detect that situation from
>> selinux_file_mprotect() -> file_map_prot_check(), because we do have a
>> non-NULL vma->vm_file so we treat it as a file execute check.  In
>> contrast, if directly creating an anonymous shared mapping with
>> PROT_EXEC via mmap(...PROT_EXEC...),  selinux_mmap_file is called with
>> a NULL file and therefore we end up applying an execmem check.
>
> Also, can you provide the lockdep traces that motivated this change?

Yes, here is it:

[   28.177939] ======================================================
[   28.177959] [ INFO: possible circular locking dependency detected ]
[   28.177980] 4.1.0-0.rc7.git0.1.fc23.x86_64+debug #1 Tainted: G        W
[   28.178002] -------------------------------------------------------
[   28.178022] sshd/1764 is trying to acquire lock:
[   28.178037]  (&isec->lock){+.+.+.}, at: [<ffffffff813b52c5>]
inode_doinit_with_dentry+0xc5/0x6a0
[   28.178078]
               but task is already holding lock:
[   28.178097]  (&mm->mmap_sem){++++++}, at: [<ffffffff81216a0f>]
vm_mmap_pgoff+0x8f/0xf0
[   28.178131]
               which lock already depends on the new lock.

[   28.178157]
               the existing dependency chain (in reverse order) is:
[   28.178180]
               -> #2 (&mm->mmap_sem){++++++}:
[   28.178201]        [<ffffffff81114017>] lock_acquire+0xc7/0x2a0
[   28.178225]        [<ffffffff8122853c>] might_fault+0x8c/0xb0
[   28.178248]        [<ffffffff8129af3a>] filldir+0x9a/0x130
[   28.178269]        [<ffffffffa019cfd6>]
xfs_dir2_block_getdents.isra.12+0x1a6/0x1d0 [xfs]
[   28.178330]        [<ffffffffa019dae4>] xfs_readdir+0x1c4/0x360 [xfs]
[   28.178368]        [<ffffffffa01a0a5b>] xfs_file_readdir+0x2b/0x30 [xfs]
[   28.178404]        [<ffffffff8129ad0a>] iterate_dir+0x9a/0x140
[   28.178425]        [<ffffffff8129b241>] SyS_getdents+0x91/0x120
[   28.178447]        [<ffffffff818a016e>] system_call_fastpath+0x12/0x76
[   28.178471]
               -> #1 (&xfs_dir_ilock_class){++++.+}:
[   28.178494]        [<ffffffff81114017>] lock_acquire+0xc7/0x2a0
[   28.178515]        [<ffffffff8110bee7>] down_read_nested+0x57/0xa0
[   28.178538]        [<ffffffffa01b2ed1>] xfs_ilock+0x171/0x390 [xfs]
[   28.178579]        [<ffffffffa01b3168>]
xfs_ilock_attr_map_shared+0x38/0x50 [xfs]
[   28.178618]        [<ffffffffa0145d8d>] xfs_attr_get+0xbd/0x1b0 [xfs]
[   28.178651]        [<ffffffffa01c44ad>] xfs_xattr_get+0x3d/0x80 [xfs]
[   28.178688]        [<ffffffff812b022f>] generic_getxattr+0x4f/0x70
[   28.178711]        [<ffffffff813b5372>] inode_doinit_with_dentry+0x172/0x6a0
[   28.178737]        [<ffffffff813b68db>] sb_finish_set_opts+0xdb/0x260
[   28.178759]        [<ffffffff813b6ff1>] selinux_set_mnt_opts+0x331/0x670
[   28.178783]        [<ffffffff813b9b47>] superblock_doinit+0x77/0xf0
[   28.178804]        [<ffffffff813b9bd0>] delayed_superblock_init+0x10/0x20
[   28.178849]        [<ffffffff8128691a>] iterate_supers+0xba/0x120
[   28.178872]        [<ffffffff813bef23>] selinux_complete_init+0x33/0x40
[   28.178897]        [<ffffffff813cf313>] security_load_policy+0x103/0x640
[   28.178920]        [<ffffffff813c0a76>] sel_write_load+0xb6/0x790
[   28.179482]        [<ffffffff812821f7>] __vfs_write+0x37/0x110
[   28.180047]        [<ffffffff81282c89>] vfs_write+0xa9/0x1c0
[   28.180630]        [<ffffffff81283a1c>] SyS_write+0x5c/0xd0
[   28.181168]        [<ffffffff818a016e>] system_call_fastpath+0x12/0x76
[   28.181740]
               -> #0 (&isec->lock){+.+.+.}:
[   28.182808]        [<ffffffff81113331>] __lock_acquire+0x1b31/0x1e40
[   28.183347]        [<ffffffff81114017>] lock_acquire+0xc7/0x2a0
[   28.183897]        [<ffffffff8189c10d>] mutex_lock_nested+0x7d/0x460
[   28.184427]        [<ffffffff813b52c5>] inode_doinit_with_dentry+0xc5/0x6a0
[   28.184944]        [<ffffffff813b58bc>] selinux_d_instantiate+0x1c/0x20
[   28.185470]        [<ffffffff813b07ab>] security_d_instantiate+0x1b/0x30
[   28.185980]        [<ffffffff8129e8c4>] d_instantiate+0x54/0x80
[   28.186495]        [<ffffffff81211edc>] __shmem_file_setup+0xdc/0x250
[   28.186990]        [<ffffffff812164a8>] shmem_zero_setup+0x28/0x70
[   28.187500]        [<ffffffff8123471c>] mmap_region+0x66c/0x680
[   28.188006]        [<ffffffff81234a53>] do_mmap_pgoff+0x323/0x410
[   28.188500]        [<ffffffff81216a30>] vm_mmap_pgoff+0xb0/0xf0
[   28.189005]        [<ffffffff81232bf6>] SyS_mmap_pgoff+0x116/0x2b0
[   28.189490]        [<ffffffff810232bb>] SyS_mmap+0x1b/0x30
[   28.189975]        [<ffffffff818a016e>] system_call_fastpath+0x12/0x76
[   28.190474]
               other info that might help us debug this:

[   28.191901] Chain exists of:
                 &isec->lock --> &xfs_dir_ilock_class --> &mm->mmap_sem

[   28.193327]  Possible unsafe locking scenario:

[   28.194297]        CPU0                    CPU1
[   28.194774]        ----                    ----
[   28.195254]   lock(&mm->mmap_sem);
[   28.195709]                                lock(&xfs_dir_ilock_class);
[   28.196174]                                lock(&mm->mmap_sem);
[   28.196654]   lock(&isec->lock);
[   28.197108]
                *** DEADLOCK ***

[   28.198451] 1 lock held by sshd/1764:
[   28.198900]  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff81216a0f>]
vm_mmap_pgoff+0x8f/0xf0
[   28.199370]
               stack backtrace:
[   28.200276] CPU: 2 PID: 1764 Comm: sshd Tainted: G        W
4.1.0-0.rc7.git0.1.fc23.x86_64+debug #1
[   28.200753] Hardware name: VMware, Inc. VMware Virtual
Platform/440BX Desktop Reference Platform, BIOS 6.00 05/20/2014
[   28.201246]  0000000000000000 00000000eda89a94 ffff8800a86a39c8
ffffffff81896375
[   28.201771]  0000000000000000 ffffffff82a910d0 ffff8800a86a3a18
ffffffff8110fbd6
[   28.202275]  0000000000000002 ffff8800a86a3a78 0000000000000001
ffff8800a897b008
[   28.203099] Call Trace:
[   28.204237]  [<ffffffff81896375>] dump_stack+0x4c/0x65
[   28.205362]  [<ffffffff8110fbd6>] print_circular_bug+0x206/0x280
[   28.206502]  [<ffffffff81113331>] __lock_acquire+0x1b31/0x1e40
[   28.207650]  [<ffffffff81114017>] lock_acquire+0xc7/0x2a0
[   28.208758]  [<ffffffff813b52c5>] ? inode_doinit_with_dentry+0xc5/0x6a0
[   28.209902]  [<ffffffff8189c10d>] mutex_lock_nested+0x7d/0x460
[   28.211023]  [<ffffffff813b52c5>] ? inode_doinit_with_dentry+0xc5/0x6a0
[   28.212162]  [<ffffffff813b52c5>] ? inode_doinit_with_dentry+0xc5/0x6a0
[   28.213283]  [<ffffffff81027e7d>] ? native_sched_clock+0x2d/0xa0
[   28.214403]  [<ffffffff81027ef9>] ? sched_clock+0x9/0x10
[   28.215514]  [<ffffffff813b52c5>] inode_doinit_with_dentry+0xc5/0x6a0
[   28.216656]  [<ffffffff813b58bc>] selinux_d_instantiate+0x1c/0x20
[   28.217776]  [<ffffffff813b07ab>] security_d_instantiate+0x1b/0x30
[   28.218902]  [<ffffffff8129e8c4>] d_instantiate+0x54/0x80
[   28.219992]  [<ffffffff81211edc>] __shmem_file_setup+0xdc/0x250
[   28.221112]  [<ffffffff812164a8>] shmem_zero_setup+0x28/0x70
[   28.222234]  [<ffffffff8123471c>] mmap_region+0x66c/0x680
[   28.223362]  [<ffffffff81234a53>] do_mmap_pgoff+0x323/0x410
[   28.224493]  [<ffffffff81216a0f>] ? vm_mmap_pgoff+0x8f/0xf0
[   28.225643]  [<ffffffff81216a30>] vm_mmap_pgoff+0xb0/0xf0
[   28.226771]  [<ffffffff81232bf6>] SyS_mmap_pgoff+0x116/0x2b0
[   28.227900]  [<ffffffff812996ce>] ? SyS_fcntl+0x5de/0x760
[   28.229042]  [<ffffffff810232bb>] SyS_mmap+0x1b/0x30
[   28.230156]  [<ffffffff818a016e>] system_call_fastpath+0x12/0x76
[   46.520367] Adjusting tsc more than 11% (5419175 vs 7179037)


Best regards,

Morten

>
>>
>>>
>>> Reported-and-tested-by: Prarit Bhargava <prarit@redhat.com>
>>> Reported-by: Daniel Wagner <wagi@monom.org>
>>> Reported-by: Morten Stevens <mstevens@fedoraproject.org>
>>> Signed-off-by: Hugh Dickins <hughd@google.com>
>>> ---
>>>
>>>  mm/shmem.c |    8 +++++++-
>>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>>
>>> --- 4.1-rc7/mm/shmem.c  2015-04-26 19:16:31.352191298 -0700
>>> +++ linux/mm/shmem.c    2015-06-14 09:26:49.461120166 -0700
>>> @@ -3401,7 +3401,13 @@ int shmem_zero_setup(struct vm_area_stru
>>>         struct file *file;
>>>         loff_t size = vma->vm_end - vma->vm_start;
>>>
>>> -       file = shmem_file_setup("dev/zero", size, vma->vm_flags);
>>> +       /*
>>> +        * Cloning a new file under mmap_sem leads to a lock ordering conflict
>>> +        * between XFS directory reading and selinux: since this file is only
>>> +        * accessible to the user through its mapping, use S_PRIVATE flag to
>>> +        * bypass file security, in the same way as shmem_kernel_file_setup().
>>> +        */
>>> +       file = __shmem_file_setup("dev/zero", size, vma->vm_flags, S_PRIVATE);
>>>         if (IS_ERR(file))
>>>                 return PTR_ERR(file);
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>> Please read the FAQ at  http://www.tux.org/lkml/
>> _______________________________________________
>> Selinux mailing list
>> Selinux@tycho.nsa.gov
>> To unsubscribe, send email to Selinux-leave@tycho.nsa.gov.
>> To get help, send an email containing "help" to Selinux-request@tycho.nsa.gov.
>>
>>
>
> --
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> the body of a message to majordomo@vger.kernel.org
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> Please read the FAQ at  http://www.tux.org/lkml/

Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS

[Hugh Dickins]

On Wed, 8 Jul 2015, Stephen Smalley wrote:
> On 07/08/2015 09:13 AM, Stephen Smalley wrote:
> > On Sun, Jun 14, 2015 at 12:48 PM, Hugh Dickins <hughd@google.com> wrote:
> >> It appears that, at some point last year, XFS made directory handling
> >> changes which bring it into lockdep conflict with shmem_zero_setup():
> >> it is surprising that mmap() can clone an inode while holding mmap_sem,
> >> but that has been so for many years.
> >>
> >> Since those few lockdep traces that I've seen all implicated selinux,
> >> I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
> >> v3.13's commit c7277090927a ("security: shmem: implement kernel private
> >> shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
> >> the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.
> >>
> >> This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
> >> (and MAP_SHARED|MAP_ANONYMOUS).  I thought there were also drivers
> >> which cloned inode in mmap(), but if so, I cannot locate them now.
> > 
> > This causes a regression for SELinux (please, in the future, cc
> > selinux list and Paul Moore on SELinux-related changes).  In

Surprised and sorry about that, yes, I should have Cc'ed.

> > particular, this change disables SELinux checking of mprotect
> > PROT_EXEC on shared anonymous mappings, so we lose the ability to
> > control executable mappings.  That said, we are only getting that
> > check today as a side effect of our file execute check on the tmpfs
> > inode, whereas it would be better (and more consistent with the
> > mmap-time checks) to apply an execmem check in that case, in which
> > case we wouldn't care about the inode-based check.  However, I am
> > unclear on how to correctly detect that situation from
> > selinux_file_mprotect() -> file_map_prot_check(), because we do have a
> > non-NULL vma->vm_file so we treat it as a file execute check.  In
> > contrast, if directly creating an anonymous shared mapping with
> > PROT_EXEC via mmap(...PROT_EXEC...),  selinux_mmap_file is called with
> > a NULL file and therefore we end up applying an execmem check.

If you're willing to go forward with the change, rather than just call
for an immediate revert of it, then I think the right way to detect
the situation would be to check IS_PRIVATE(file_inode(vma->vm_file)),
wouldn't it?

> 
> Also, can you provide the lockdep traces that motivated this change?

Thank you for supplying that, Morten.

> 
> > 
> >>
> >> Reported-and-tested-by: Prarit Bhargava <prarit@redhat.com>
> >> Reported-by: Daniel Wagner <wagi@monom.org>
> >> Reported-by: Morten Stevens <mstevens@fedoraproject.org>
> >> Signed-off-by: Hugh Dickins <hughd@google.com>
> >> ---
> >>
> >>  mm/shmem.c |    8 +++++++-
> >>  1 file changed, 7 insertions(+), 1 deletion(-)
> >>
> >> --- 4.1-rc7/mm/shmem.c  2015-04-26 19:16:31.352191298 -0700
> >> +++ linux/mm/shmem.c    2015-06-14 09:26:49.461120166 -0700
> >> @@ -3401,7 +3401,13 @@ int shmem_zero_setup(struct vm_area_stru
> >>         struct file *file;
> >>         loff_t size = vma->vm_end - vma->vm_start;
> >>
> >> -       file = shmem_file_setup("dev/zero", size, vma->vm_flags);
> >> +       /*
> >> +        * Cloning a new file under mmap_sem leads to a lock ordering conflict
> >> +        * between XFS directory reading and selinux: since this file is only
> >> +        * accessible to the user through its mapping, use S_PRIVATE flag to
> >> +        * bypass file security, in the same way as shmem_kernel_file_setup().
> >> +        */
> >> +       file = __shmem_file_setup("dev/zero", size, vma->vm_flags, S_PRIVATE);
> >>         if (IS_ERR(file))
> >>                 return PTR_ERR(file);
> >>
> >> --
> >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> >> the body of a message to majordomo@vger.kernel.org
> >> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >> Please read the FAQ at  http://www.tux.org/lkml/
> > _______________________________________________
> > Selinux mailing list
> > Selinux@tycho.nsa.gov
> > To unsubscribe, send email to Selinux-leave@tycho.nsa.gov.
> > To get help, send an email containing "help" to Selinux-request@tycho.nsa.gov.
> > 
> > 
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
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> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
> 

Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS

[Stephen Smalley]

On 07/09/2015 04:23 AM, Hugh Dickins wrote:
> On Wed, 8 Jul 2015, Stephen Smalley wrote:
>> On 07/08/2015 09:13 AM, Stephen Smalley wrote:
>>> On Sun, Jun 14, 2015 at 12:48 PM, Hugh Dickins <hughd@google.com> wrote:
>>>> It appears that, at some point last year, XFS made directory handling
>>>> changes which bring it into lockdep conflict with shmem_zero_setup():
>>>> it is surprising that mmap() can clone an inode while holding mmap_sem,
>>>> but that has been so for many years.
>>>>
>>>> Since those few lockdep traces that I've seen all implicated selinux,
>>>> I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
>>>> v3.13's commit c7277090927a ("security: shmem: implement kernel private
>>>> shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
>>>> the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.
>>>>
>>>> This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
>>>> (and MAP_SHARED|MAP_ANONYMOUS).  I thought there were also drivers
>>>> which cloned inode in mmap(), but if so, I cannot locate them now.
>>>
>>> This causes a regression for SELinux (please, in the future, cc
>>> selinux list and Paul Moore on SELinux-related changes).  In
> 
> Surprised and sorry about that, yes, I should have Cc'ed.
> 
>>> particular, this change disables SELinux checking of mprotect
>>> PROT_EXEC on shared anonymous mappings, so we lose the ability to
>>> control executable mappings.  That said, we are only getting that
>>> check today as a side effect of our file execute check on the tmpfs
>>> inode, whereas it would be better (and more consistent with the
>>> mmap-time checks) to apply an execmem check in that case, in which
>>> case we wouldn't care about the inode-based check.  However, I am
>>> unclear on how to correctly detect that situation from
>>> selinux_file_mprotect() -> file_map_prot_check(), because we do have a
>>> non-NULL vma->vm_file so we treat it as a file execute check.  In
>>> contrast, if directly creating an anonymous shared mapping with
>>> PROT_EXEC via mmap(...PROT_EXEC...),  selinux_mmap_file is called with
>>> a NULL file and therefore we end up applying an execmem check.
> 
> If you're willing to go forward with the change, rather than just call
> for an immediate revert of it, then I think the right way to detect
> the situation would be to check IS_PRIVATE(file_inode(vma->vm_file)),
> wouldn't it?

That seems misleading and might trigger execmem checks on non-shmem
inodes.  S_PRIVATE was originally introduced for fs-internal inodes that
are never directly exposed to userspace, originally for reiserfs xattr
inodes (reiserfs xattrs are internally implemented as their own files
that are hidden from userspace) and later also applied to anon inodes.
It would be better if we had an explicit way of testing that we are
dealing with an anonymous shared mapping in selinux_file_mprotect() ->
file_map_prot_check().

Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS

[Hugh Dickins]

On Thu, 9 Jul 2015, Stephen Smalley wrote:
> On 07/09/2015 04:23 AM, Hugh Dickins wrote:
> > On Wed, 8 Jul 2015, Stephen Smalley wrote:
> >> On 07/08/2015 09:13 AM, Stephen Smalley wrote:
> >>> On Sun, Jun 14, 2015 at 12:48 PM, Hugh Dickins <hughd@google.com> wrote:
> >>>> It appears that, at some point last year, XFS made directory handling
> >>>> changes which bring it into lockdep conflict with shmem_zero_setup():
> >>>> it is surprising that mmap() can clone an inode while holding mmap_sem,
> >>>> but that has been so for many years.
> >>>>
> >>>> Since those few lockdep traces that I've seen all implicated selinux,
> >>>> I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
> >>>> v3.13's commit c7277090927a ("security: shmem: implement kernel private
> >>>> shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
> >>>> the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.
> >>>>
> >>>> This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
> >>>> (and MAP_SHARED|MAP_ANONYMOUS).  I thought there were also drivers
> >>>> which cloned inode in mmap(), but if so, I cannot locate them now.
> >>>
> >>> This causes a regression for SELinux (please, in the future, cc
> >>> selinux list and Paul Moore on SELinux-related changes).  In
> > 
> > Surprised and sorry about that, yes, I should have Cc'ed.
> > 
> >>> particular, this change disables SELinux checking of mprotect
> >>> PROT_EXEC on shared anonymous mappings, so we lose the ability to
> >>> control executable mappings.  That said, we are only getting that
> >>> check today as a side effect of our file execute check on the tmpfs
> >>> inode, whereas it would be better (and more consistent with the
> >>> mmap-time checks) to apply an execmem check in that case, in which
> >>> case we wouldn't care about the inode-based check.  However, I am
> >>> unclear on how to correctly detect that situation from
> >>> selinux_file_mprotect() -> file_map_prot_check(), because we do have a
> >>> non-NULL vma->vm_file so we treat it as a file execute check.  In
> >>> contrast, if directly creating an anonymous shared mapping with
> >>> PROT_EXEC via mmap(...PROT_EXEC...),  selinux_mmap_file is called with
> >>> a NULL file and therefore we end up applying an execmem check.
> > 
> > If you're willing to go forward with the change, rather than just call
> > for an immediate revert of it, then I think the right way to detect
> > the situation would be to check IS_PRIVATE(file_inode(vma->vm_file)),
> > wouldn't it?
> 
> That seems misleading and might trigger execmem checks on non-shmem
> inodes.  S_PRIVATE was originally introduced for fs-internal inodes that
> are never directly exposed to userspace, originally for reiserfs xattr
> inodes (reiserfs xattrs are internally implemented as their own files
> that are hidden from userspace) and later also applied to anon inodes.
> It would be better if we had an explicit way of testing that we are
> dealing with an anonymous shared mapping in selinux_file_mprotect() ->
> file_map_prot_check().

But how would any of those original S_PRIVATE inodes arrive at
selinux_file_mprotect()?  Now we have added the anon shared mmap case
which can arrive there, but the S_PRIVATE check seems just the right
tool for the job of distinguishing those from the user-visible inodes.

I don't see how adding some other flag for this case would be better
- though certainly I can see that adding an "anon shared shmem"
comment on its use in that check would be helpful.

Or is there some further difficulty in this use of S_PRIVATE, beyond
the mprotect case that you've mentioned?  Unless there is some further
difficulty, duplicating all the code relating to S_PRIVATE for a
differently named flag seems counter-productive to me.

(There is a bool shmem_mapping(mapping) that could be used to confirm
that the inode you're looking at indeed belongs to shmem; but of
course that would say yes on all the user-visible shmem inodes too,
so it wouldn't be a useful test on its own, and I don't see that
adding it to an S_PRIVATE test would add any real value.)

Probably you were hoping that there's already some distinguishing
feature of anon shared shmem inodes that you could check: I can't
think of one offhand, beyond S_PRIVATE: if there is another,
it would be accidental.

Hugh

Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS

[Stephen Smalley]

On 07/10/2015 03:48 AM, Hugh Dickins wrote:
> On Thu, 9 Jul 2015, Stephen Smalley wrote:
>> On 07/09/2015 04:23 AM, Hugh Dickins wrote:
>>> On Wed, 8 Jul 2015, Stephen Smalley wrote:
>>>> On 07/08/2015 09:13 AM, Stephen Smalley wrote:
>>>>> On Sun, Jun 14, 2015 at 12:48 PM, Hugh Dickins <hughd@google.com> wrote:
>>>>>> It appears that, at some point last year, XFS made directory handling
>>>>>> changes which bring it into lockdep conflict with shmem_zero_setup():
>>>>>> it is surprising that mmap() can clone an inode while holding mmap_sem,
>>>>>> but that has been so for many years.
>>>>>>
>>>>>> Since those few lockdep traces that I've seen all implicated selinux,
>>>>>> I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
>>>>>> v3.13's commit c7277090927a ("security: shmem: implement kernel private
>>>>>> shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
>>>>>> the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.
>>>>>>
>>>>>> This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
>>>>>> (and MAP_SHARED|MAP_ANONYMOUS).  I thought there were also drivers
>>>>>> which cloned inode in mmap(), but if so, I cannot locate them now.
>>>>>
>>>>> This causes a regression for SELinux (please, in the future, cc
>>>>> selinux list and Paul Moore on SELinux-related changes).  In
>>>
>>> Surprised and sorry about that, yes, I should have Cc'ed.
>>>
>>>>> particular, this change disables SELinux checking of mprotect
>>>>> PROT_EXEC on shared anonymous mappings, so we lose the ability to
>>>>> control executable mappings.  That said, we are only getting that
>>>>> check today as a side effect of our file execute check on the tmpfs
>>>>> inode, whereas it would be better (and more consistent with the
>>>>> mmap-time checks) to apply an execmem check in that case, in which
>>>>> case we wouldn't care about the inode-based check.  However, I am
>>>>> unclear on how to correctly detect that situation from
>>>>> selinux_file_mprotect() -> file_map_prot_check(), because we do have a
>>>>> non-NULL vma->vm_file so we treat it as a file execute check.  In
>>>>> contrast, if directly creating an anonymous shared mapping with
>>>>> PROT_EXEC via mmap(...PROT_EXEC...),  selinux_mmap_file is called with
>>>>> a NULL file and therefore we end up applying an execmem check.
>>>
>>> If you're willing to go forward with the change, rather than just call
>>> for an immediate revert of it, then I think the right way to detect
>>> the situation would be to check IS_PRIVATE(file_inode(vma->vm_file)),
>>> wouldn't it?
>>
>> That seems misleading and might trigger execmem checks on non-shmem
>> inodes.  S_PRIVATE was originally introduced for fs-internal inodes that
>> are never directly exposed to userspace, originally for reiserfs xattr
>> inodes (reiserfs xattrs are internally implemented as their own files
>> that are hidden from userspace) and later also applied to anon inodes.
>> It would be better if we had an explicit way of testing that we are
>> dealing with an anonymous shared mapping in selinux_file_mprotect() ->
>> file_map_prot_check().
> 
> But how would any of those original S_PRIVATE inodes arrive at
> selinux_file_mprotect()?  Now we have added the anon shared mmap case
> which can arrive there, but the S_PRIVATE check seems just the right
> tool for the job of distinguishing those from the user-visible inodes.
> 
> I don't see how adding some other flag for this case would be better
> - though certainly I can see that adding an "anon shared shmem"
> comment on its use in that check would be helpful.
> 
> Or is there some further difficulty in this use of S_PRIVATE, beyond
> the mprotect case that you've mentioned?  Unless there is some further
> difficulty, duplicating all the code relating to S_PRIVATE for a
> differently named flag seems counter-productive to me.

S_PRIVATE is supposed to disable all security processing on the inode,
and often this is checked in the security framework
(security/security.c) even before we reach the SELinux hook and causes
an immediate return there.  In the case of mprotect, we do reach the
SELinux code since the hook is on the vma, not merely the inode, so we
could apply an execmem check in the SELinux code if IS_PRIVATE() instead
of file execute.

However, I was trying to figure out if the fact that S_PRIVATE also
would disable any read/write checking by SELinux on the inode could
potentially open up a bypass of security policy.  That would only be an
issue if the file returned by shmem_zero_setup() was ever linked to an
open file descriptor that could be inherited across a fork+exec or
passed across local socket IPC or binder IPC and thereby shared across
different security contexts. Uses of shmem_zero_setup() include mmap
MAP_ANONYMOUS|MAP_SHARED, drivers/staging/android/ashmem.c (from
ashmem_mmap if VM_SHARED), and drivers/char/mem.c (from mmap_zero if
VM_SHARED).  That all seems fine AFAICS.

> (There is a bool shmem_mapping(mapping) that could be used to confirm
> that the inode you're looking at indeed belongs to shmem; but of
> course that would say yes on all the user-visible shmem inodes too,
> so it wouldn't be a useful test on its own, and I don't see that
> adding it to an S_PRIVATE test would add any real value.)
> 
> Probably you were hoping that there's already some distinguishing
> feature of anon shared shmem inodes that you could check: I can't
> think of one offhand, beyond S_PRIVATE: if there is another,
> it would be accidental.

Yes, I was hoping for that.  Ok, I'll spin up a patch for adding an
IS_PRIVATE() test to SELinux file_map_prot_check() and cc you all on it.

Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS

[Morten Stevens]

2015-06-17 13:45 GMT+02:00 Morten Stevens <mstevens@fedoraproject.org>:
> 2015-06-15 8:09 GMT+02:00 Daniel Wagner <wagi@monom.org>:
>> On 06/14/2015 06:48 PM, Hugh Dickins wrote:
>>> It appears that, at some point last year, XFS made directory handling
>>> changes which bring it into lockdep conflict with shmem_zero_setup():
>>> it is surprising that mmap() can clone an inode while holding mmap_sem,
>>> but that has been so for many years.
>>>
>>> Since those few lockdep traces that I've seen all implicated selinux,
>>> I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
>>> v3.13's commit c7277090927a ("security: shmem: implement kernel private
>>> shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
>>> the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.
>>>
>>> This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
>>> (and MAP_SHARED|MAP_ANONYMOUS).  I thought there were also drivers
>>> which cloned inode in mmap(), but if so, I cannot locate them now.
>>>
>>> Reported-and-tested-by: Prarit Bhargava <prarit@redhat.com>
>>> Reported-by: Daniel Wagner <wagi@monom.org>
>>
>> Reported-and-tested-by: Daniel Wagner <wagi@monom.org>
>>
>> Sorry for the long delay. It took me a while to figure out my original
>> setup. I could verify that this patch made the lockdep message go away
>> on 4.0-rc6 and also on 4.1-rc8.
>
> Yes, it's also fixed for me after applying this patch to 4.1-rc8.

Here is another deadlock with the latest 4.2.0-rc3:

Jul 22 14:36:40 fc23 kernel:
======================================================
Jul 22 14:36:40 fc23 kernel: [ INFO: possible circular locking
dependency detected ]
Jul 22 14:36:40 fc23 kernel: 4.2.0-0.rc3.git0.1.fc24.x86_64+debug #1
Tainted: G        W
Jul 22 14:36:40 fc23 kernel:
-------------------------------------------------------
Jul 22 14:36:40 fc23 kernel: httpd/1597 is trying to acquire lock:
Jul 22 14:36:40 fc23 kernel: (&ids->rwsem){+++++.}, at:
[<ffffffff81385354>] shm_close+0x34/0x130
Jul 22 14:36:40 fc23 kernel: #012but task is already holding lock:
Jul 22 14:36:40 fc23 kernel: (&mm->mmap_sem){++++++}, at:
[<ffffffff81386bbb>] SyS_shmdt+0x4b/0x180
Jul 22 14:36:40 fc23 kernel: #012which lock already depends on the new lock.
Jul 22 14:36:40 fc23 kernel: #012the existing dependency chain (in
reverse order) is:
Jul 22 14:36:40 fc23 kernel: #012-> #3 (&mm->mmap_sem){++++++}:
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81109a07>] lock_acquire+0xc7/0x270
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81217baa>] __might_fault+0x7a/0xa0
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81284a1e>] filldir+0x9e/0x130
Jul 22 14:36:40 fc23 kernel:       [<ffffffffa019bb08>]
xfs_dir2_block_getdents.isra.12+0x198/0x1c0 [xfs]
Jul 22 14:36:40 fc23 kernel:       [<ffffffffa019c5b4>]
xfs_readdir+0x1b4/0x330 [xfs]
Jul 22 14:36:40 fc23 kernel:       [<ffffffffa019f38b>]
xfs_file_readdir+0x2b/0x30 [xfs]
Jul 22 14:36:40 fc23 kernel:       [<ffffffff812847e7>] iterate_dir+0x97/0x130
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81284d21>] SyS_getdents+0x91/0x120
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81871d2e>]
entry_SYSCALL_64_fastpath+0x12/0x76
Jul 22 14:36:40 fc23 kernel: #012-> #2 (&xfs_dir_ilock_class){++++.+}:
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81109a07>] lock_acquire+0xc7/0x270
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81101e97>]
down_read_nested+0x57/0xa0
Jul 22 14:36:40 fc23 kernel:       [<ffffffffa01b0e57>]
xfs_ilock+0x167/0x350 [xfs]
Jul 22 14:36:40 fc23 kernel:       [<ffffffffa01b10b8>]
xfs_ilock_attr_map_shared+0x38/0x50 [xfs]
Jul 22 14:36:40 fc23 kernel:       [<ffffffffa014799d>]
xfs_attr_get+0xbd/0x190 [xfs]
Jul 22 14:36:40 fc23 kernel:       [<ffffffffa01c17ad>]
xfs_xattr_get+0x3d/0x70 [xfs]
Jul 22 14:36:40 fc23 kernel:       [<ffffffff8129962f>]
generic_getxattr+0x4f/0x70
Jul 22 14:36:40 fc23 kernel:       [<ffffffff8139ba52>]
inode_doinit_with_dentry+0x162/0x670
Jul 22 14:36:40 fc23 kernel:       [<ffffffff8139cf69>]
sb_finish_set_opts+0xd9/0x230
Jul 22 14:36:40 fc23 kernel:       [<ffffffff8139d66c>]
selinux_set_mnt_opts+0x35c/0x660
Jul 22 14:36:40 fc23 kernel:       [<ffffffff8139ff97>]
superblock_doinit+0x77/0xf0
Jul 22 14:36:40 fc23 kernel:       [<ffffffff813a0020>]
delayed_superblock_init+0x10/0x20
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81272d23>]
iterate_supers+0xb3/0x110
Jul 22 14:36:40 fc23 kernel:       [<ffffffff813a4e5f>]
selinux_complete_init+0x2f/0x40
Jul 22 14:36:40 fc23 kernel:       [<ffffffff813b47a3>]
security_load_policy+0x103/0x600
Jul 22 14:36:40 fc23 kernel:       [<ffffffff813a6901>]
sel_write_load+0xc1/0x750
Jul 22 14:36:40 fc23 kernel:       [<ffffffff8126e817>] __vfs_write+0x37/0x100
Jul 22 14:36:40 fc23 kernel:       [<ffffffff8126f229>] vfs_write+0xa9/0x1a0
Jul 22 14:36:40 fc23 kernel:       [<ffffffff8126ff48>] SyS_write+0x58/0xd0
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81871d2e>]
entry_SYSCALL_64_fastpath+0x12/0x76
Jul 22 14:36:40 fc23 kernel: #012-> #1 (&isec->lock){+.+.+.}:
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81109a07>] lock_acquire+0xc7/0x270
Jul 22 14:36:40 fc23 kernel:       [<ffffffff8186de8f>]
mutex_lock_nested+0x7f/0x3e0
Jul 22 14:36:40 fc23 kernel:       [<ffffffff8139b9a9>]
inode_doinit_with_dentry+0xb9/0x670
Jul 22 14:36:40 fc23 kernel:       [<ffffffff8139bf7c>]
selinux_d_instantiate+0x1c/0x20
Jul 22 14:36:40 fc23 kernel:       [<ffffffff813955f6>]
security_d_instantiate+0x36/0x60
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81287c34>] d_instantiate+0x54/0x70
Jul 22 14:36:40 fc23 kernel:       [<ffffffff8120111c>]
__shmem_file_setup+0xdc/0x240
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81201290>]
shmem_file_setup+0x10/0x20
Jul 22 14:36:40 fc23 kernel:       [<ffffffff813856e0>] newseg+0x290/0x3a0
Jul 22 14:36:40 fc23 kernel:       [<ffffffff8137e278>] ipcget+0x208/0x2d0
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81386074>] SyS_shmget+0x54/0x70
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81871d2e>]
entry_SYSCALL_64_fastpath+0x12/0x76
Jul 22 14:36:40 fc23 kernel: #012-> #0 (&ids->rwsem){+++++.}:
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81108df8>]
__lock_acquire+0x1a78/0x1d00
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81109a07>] lock_acquire+0xc7/0x270
Jul 22 14:36:40 fc23 kernel:       [<ffffffff8186efba>] down_write+0x5a/0xc0
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81385354>] shm_close+0x34/0x130
Jul 22 14:36:40 fc23 kernel:       [<ffffffff812203a5>] remove_vma+0x45/0x80
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81222a30>] do_munmap+0x2b0/0x460
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81386c25>] SyS_shmdt+0xb5/0x180
Jul 22 14:36:40 fc23 kernel:       [<ffffffff81871d2e>]
entry_SYSCALL_64_fastpath+0x12/0x76
Jul 22 14:36:40 fc23 kernel: #012other info that might help us debug this:
Jul 22 14:36:40 fc23 kernel: Chain exists of:#012  &ids->rwsem -->
&xfs_dir_ilock_class --> &mm->mmap_sem
Jul 22 14:36:40 fc23 kernel: Possible unsafe locking scenario:
Jul 22 14:36:40 fc23 kernel:       CPU0                    CPU1
Jul 22 14:36:40 fc23 kernel:       ----                    ----
Jul 22 14:36:40 fc23 kernel:  lock(&mm->mmap_sem);
Jul 22 14:36:40 fc23 kernel:
lock(&xfs_dir_ilock_class);
Jul 22 14:36:40 fc23 kernel:                               lock(&mm->mmap_sem);
Jul 22 14:36:40 fc23 kernel:  lock(&ids->rwsem);
Jul 22 14:36:40 fc23 kernel: #012 *** DEADLOCK ***
Jul 22 14:36:40 fc23 kernel: 1 lock held by httpd/1597:
Jul 22 14:36:40 fc23 kernel: #0:  (&mm->mmap_sem){++++++}, at:
[<ffffffff81386bbb>] SyS_shmdt+0x4b/0x180
Jul 22 14:36:40 fc23 kernel: #012stack backtrace:
Jul 22 14:36:40 fc23 kernel: CPU: 7 PID: 1597 Comm: httpd Tainted: G
     W       4.2.0-0.rc3.git0.1.fc24.x86_64+debug #1
Jul 22 14:36:40 fc23 kernel: Hardware name: VMware, Inc. VMware
Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00
05/20/2014
Jul 22 14:36:40 fc23 kernel: 0000000000000000 000000006cb6fe9d
ffff88019ff07c58 ffffffff81868175
Jul 22 14:36:40 fc23 kernel: 0000000000000000 ffffffff82aea390
ffff88019ff07ca8 ffffffff81105903
Jul 22 14:36:40 fc23 kernel: ffff88019ff07c78 ffff88019ff07d08
0000000000000001 ffff8800b75108f0
Jul 22 14:36:40 fc23 kernel: Call Trace:
Jul 22 14:36:40 fc23 kernel: [<ffffffff81868175>] dump_stack+0x4c/0x65
Jul 22 14:36:40 fc23 kernel: [<ffffffff81105903>] print_circular_bug+0x1e3/0x250
Jul 22 14:36:40 fc23 kernel: [<ffffffff81108df8>] __lock_acquire+0x1a78/0x1d00
Jul 22 14:36:40 fc23 kernel: [<ffffffff81220c33>] ? unlink_file_vma+0x33/0x60
Jul 22 14:36:40 fc23 kernel: [<ffffffff81109a07>] lock_acquire+0xc7/0x270
Jul 22 14:36:40 fc23 kernel: [<ffffffff81385354>] ? shm_close+0x34/0x130
Jul 22 14:36:40 fc23 kernel: [<ffffffff8186efba>] down_write+0x5a/0xc0
Jul 22 14:36:40 fc23 kernel: [<ffffffff81385354>] ? shm_close+0x34/0x130
Jul 22 14:36:40 fc23 kernel: [<ffffffff81385354>] shm_close+0x34/0x130
Jul 22 14:36:40 fc23 kernel: [<ffffffff812203a5>] remove_vma+0x45/0x80
Jul 22 14:36:40 fc23 kernel: [<ffffffff81222a30>] do_munmap+0x2b0/0x460
Jul 22 14:36:40 fc23 kernel: [<ffffffff81386bbb>] ? SyS_shmdt+0x4b/0x180
Jul 22 14:36:40 fc23 kernel: [<ffffffff81386c25>] SyS_shmdt+0xb5/0x180
Jul 22 14:36:40 fc23 kernel: [<ffffffff81871d2e>]
entry_SYSCALL_64_fastpath+0x12/0x76

Best regards,

Morten

Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS

[Stephen Smalley]

On 07/22/2015 08:46 AM, Morten Stevens wrote:
> 2015-06-17 13:45 GMT+02:00 Morten Stevens <mstevens@fedoraproject.org>:
>> 2015-06-15 8:09 GMT+02:00 Daniel Wagner <wagi@monom.org>:
>>> On 06/14/2015 06:48 PM, Hugh Dickins wrote:
>>>> It appears that, at some point last year, XFS made directory handling
>>>> changes which bring it into lockdep conflict with shmem_zero_setup():
>>>> it is surprising that mmap() can clone an inode while holding mmap_sem,
>>>> but that has been so for many years.
>>>>
>>>> Since those few lockdep traces that I've seen all implicated selinux,
>>>> I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
>>>> v3.13's commit c7277090927a ("security: shmem: implement kernel private
>>>> shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
>>>> the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.
>>>>
>>>> This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
>>>> (and MAP_SHARED|MAP_ANONYMOUS).  I thought there were also drivers
>>>> which cloned inode in mmap(), but if so, I cannot locate them now.
>>>>
>>>> Reported-and-tested-by: Prarit Bhargava <prarit@redhat.com>
>>>> Reported-by: Daniel Wagner <wagi@monom.org>
>>>
>>> Reported-and-tested-by: Daniel Wagner <wagi@monom.org>
>>>
>>> Sorry for the long delay. It took me a while to figure out my original
>>> setup. I could verify that this patch made the lockdep message go away
>>> on 4.0-rc6 and also on 4.1-rc8.
>>
>> Yes, it's also fixed for me after applying this patch to 4.1-rc8.
> 
> Here is another deadlock with the latest 4.2.0-rc3:
> 
> Jul 22 14:36:40 fc23 kernel:
> ======================================================
> Jul 22 14:36:40 fc23 kernel: [ INFO: possible circular locking
> dependency detected ]
> Jul 22 14:36:40 fc23 kernel: 4.2.0-0.rc3.git0.1.fc24.x86_64+debug #1
> Tainted: G        W
> Jul 22 14:36:40 fc23 kernel:
> -------------------------------------------------------
> Jul 22 14:36:40 fc23 kernel: httpd/1597 is trying to acquire lock:
> Jul 22 14:36:40 fc23 kernel: (&ids->rwsem){+++++.}, at:
> [<ffffffff81385354>] shm_close+0x34/0x130
> Jul 22 14:36:40 fc23 kernel: #012but task is already holding lock:
> Jul 22 14:36:40 fc23 kernel: (&mm->mmap_sem){++++++}, at:
> [<ffffffff81386bbb>] SyS_shmdt+0x4b/0x180
> Jul 22 14:36:40 fc23 kernel: #012which lock already depends on the new lock.
> Jul 22 14:36:40 fc23 kernel: #012the existing dependency chain (in
> reverse order) is:
> Jul 22 14:36:40 fc23 kernel: #012-> #3 (&mm->mmap_sem){++++++}:
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81109a07>] lock_acquire+0xc7/0x270
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81217baa>] __might_fault+0x7a/0xa0
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81284a1e>] filldir+0x9e/0x130
> Jul 22 14:36:40 fc23 kernel:       [<ffffffffa019bb08>]
> xfs_dir2_block_getdents.isra.12+0x198/0x1c0 [xfs]
> Jul 22 14:36:40 fc23 kernel:       [<ffffffffa019c5b4>]
> xfs_readdir+0x1b4/0x330 [xfs]
> Jul 22 14:36:40 fc23 kernel:       [<ffffffffa019f38b>]
> xfs_file_readdir+0x2b/0x30 [xfs]
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff812847e7>] iterate_dir+0x97/0x130
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81284d21>] SyS_getdents+0x91/0x120
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81871d2e>]
> entry_SYSCALL_64_fastpath+0x12/0x76
> Jul 22 14:36:40 fc23 kernel: #012-> #2 (&xfs_dir_ilock_class){++++.+}:
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81109a07>] lock_acquire+0xc7/0x270
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81101e97>]
> down_read_nested+0x57/0xa0
> Jul 22 14:36:40 fc23 kernel:       [<ffffffffa01b0e57>]
> xfs_ilock+0x167/0x350 [xfs]
> Jul 22 14:36:40 fc23 kernel:       [<ffffffffa01b10b8>]
> xfs_ilock_attr_map_shared+0x38/0x50 [xfs]
> Jul 22 14:36:40 fc23 kernel:       [<ffffffffa014799d>]
> xfs_attr_get+0xbd/0x190 [xfs]
> Jul 22 14:36:40 fc23 kernel:       [<ffffffffa01c17ad>]
> xfs_xattr_get+0x3d/0x70 [xfs]
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff8129962f>]
> generic_getxattr+0x4f/0x70
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff8139ba52>]
> inode_doinit_with_dentry+0x162/0x670
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff8139cf69>]
> sb_finish_set_opts+0xd9/0x230
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff8139d66c>]
> selinux_set_mnt_opts+0x35c/0x660
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff8139ff97>]
> superblock_doinit+0x77/0xf0
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff813a0020>]
> delayed_superblock_init+0x10/0x20
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81272d23>]
> iterate_supers+0xb3/0x110
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff813a4e5f>]
> selinux_complete_init+0x2f/0x40
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff813b47a3>]
> security_load_policy+0x103/0x600
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff813a6901>]
> sel_write_load+0xc1/0x750
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff8126e817>] __vfs_write+0x37/0x100
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff8126f229>] vfs_write+0xa9/0x1a0
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff8126ff48>] SyS_write+0x58/0xd0
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81871d2e>]
> entry_SYSCALL_64_fastpath+0x12/0x76
> Jul 22 14:36:40 fc23 kernel: #012-> #1 (&isec->lock){+.+.+.}:
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81109a07>] lock_acquire+0xc7/0x270
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff8186de8f>]
> mutex_lock_nested+0x7f/0x3e0
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff8139b9a9>]
> inode_doinit_with_dentry+0xb9/0x670
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff8139bf7c>]
> selinux_d_instantiate+0x1c/0x20
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff813955f6>]
> security_d_instantiate+0x36/0x60
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81287c34>] d_instantiate+0x54/0x70
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff8120111c>]
> __shmem_file_setup+0xdc/0x240
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81201290>]
> shmem_file_setup+0x10/0x20
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff813856e0>] newseg+0x290/0x3a0
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff8137e278>] ipcget+0x208/0x2d0
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81386074>] SyS_shmget+0x54/0x70
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81871d2e>]
> entry_SYSCALL_64_fastpath+0x12/0x76
> Jul 22 14:36:40 fc23 kernel: #012-> #0 (&ids->rwsem){+++++.}:
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81108df8>]
> __lock_acquire+0x1a78/0x1d00
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81109a07>] lock_acquire+0xc7/0x270
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff8186efba>] down_write+0x5a/0xc0
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81385354>] shm_close+0x34/0x130
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff812203a5>] remove_vma+0x45/0x80
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81222a30>] do_munmap+0x2b0/0x460
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81386c25>] SyS_shmdt+0xb5/0x180
> Jul 22 14:36:40 fc23 kernel:       [<ffffffff81871d2e>]
> entry_SYSCALL_64_fastpath+0x12/0x76
> Jul 22 14:36:40 fc23 kernel: #012other info that might help us debug this:
> Jul 22 14:36:40 fc23 kernel: Chain exists of:#012  &ids->rwsem -->
> &xfs_dir_ilock_class --> &mm->mmap_sem
> Jul 22 14:36:40 fc23 kernel: Possible unsafe locking scenario:
> Jul 22 14:36:40 fc23 kernel:       CPU0                    CPU1
> Jul 22 14:36:40 fc23 kernel:       ----                    ----
> Jul 22 14:36:40 fc23 kernel:  lock(&mm->mmap_sem);
> Jul 22 14:36:40 fc23 kernel:
> lock(&xfs_dir_ilock_class);
> Jul 22 14:36:40 fc23 kernel:                               lock(&mm->mmap_sem);
> Jul 22 14:36:40 fc23 kernel:  lock(&ids->rwsem);
> Jul 22 14:36:40 fc23 kernel: #012 *** DEADLOCK ***
> Jul 22 14:36:40 fc23 kernel: 1 lock held by httpd/1597:
> Jul 22 14:36:40 fc23 kernel: #0:  (&mm->mmap_sem){++++++}, at:
> [<ffffffff81386bbb>] SyS_shmdt+0x4b/0x180
> Jul 22 14:36:40 fc23 kernel: #012stack backtrace:
> Jul 22 14:36:40 fc23 kernel: CPU: 7 PID: 1597 Comm: httpd Tainted: G
>      W       4.2.0-0.rc3.git0.1.fc24.x86_64+debug #1
> Jul 22 14:36:40 fc23 kernel: Hardware name: VMware, Inc. VMware
> Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00
> 05/20/2014
> Jul 22 14:36:40 fc23 kernel: 0000000000000000 000000006cb6fe9d
> ffff88019ff07c58 ffffffff81868175
> Jul 22 14:36:40 fc23 kernel: 0000000000000000 ffffffff82aea390
> ffff88019ff07ca8 ffffffff81105903
> Jul 22 14:36:40 fc23 kernel: ffff88019ff07c78 ffff88019ff07d08
> 0000000000000001 ffff8800b75108f0
> Jul 22 14:36:40 fc23 kernel: Call Trace:
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81868175>] dump_stack+0x4c/0x65
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81105903>] print_circular_bug+0x1e3/0x250
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81108df8>] __lock_acquire+0x1a78/0x1d00
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81220c33>] ? unlink_file_vma+0x33/0x60
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81109a07>] lock_acquire+0xc7/0x270
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81385354>] ? shm_close+0x34/0x130
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8186efba>] down_write+0x5a/0xc0
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81385354>] ? shm_close+0x34/0x130
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81385354>] shm_close+0x34/0x130
> Jul 22 14:36:40 fc23 kernel: [<ffffffff812203a5>] remove_vma+0x45/0x80
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81222a30>] do_munmap+0x2b0/0x460
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81386bbb>] ? SyS_shmdt+0x4b/0x180
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81386c25>] SyS_shmdt+0xb5/0x180
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81871d2e>]
> entry_SYSCALL_64_fastpath+0x12/0x76
> 
> Best regards,
> 
> Morten

I would think that we could flip shm over to using
shmem_kernel_file_setup(), but you might still encounter the same
warning on a hugetlb segment, unless we also start marking those as
private.  I am a little concerned that we are playing whack-a-mole.
What's the original change that has caused these deadlock scenarios to
arise now (I see the original patch descriptions mentions XFS directory
handling changes, but not clear on the details, nor on how this is
relevant to shmem inodes), and are these real deadlock scenarios or
merely false positives that you are trying to eliminate?