From: Hugh Dickins <hughd@google.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Prarit Bhargava <prarit@redhat.com>,
Morten Stevens <mstevens@fedoraproject.org>,
Daniel Wagner <wagi@monom.org>,
Dave Chinner <david@fromorbit.com>,
Eric Paris <eparis@redhat.com>,
Eric Sandeen <esandeen@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: mm: shmem_zero_setup skip security check and lockdep conflict with XFS
Date: Sun, 14 Jun 2015 09:48:09 -0700 (PDT) [thread overview]
Message-ID: <alpine.LSU.2.11.1506140944380.11018@eggly.anvils> (raw)
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);
next reply other threads:[~2015-06-14 16:48 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-14 16:48 Hugh Dickins [this message]
2015-06-15 6:09 ` mm: shmem_zero_setup skip security check and lockdep conflict with XFS Daniel Wagner
2015-06-16 20:27 ` Hugh Dickins
2015-06-17 11:45 ` Morten Stevens
2015-06-18 0:22 ` Hugh Dickins
2015-07-22 12:46 ` Morten Stevens
2015-07-22 21:07 ` Stephen Smalley
2015-07-08 13:13 ` Stephen Smalley
2015-07-08 16:37 ` Stephen Smalley
2015-07-08 20:37 ` Morten Stevens
2015-07-09 8:23 ` Hugh Dickins
2015-07-09 12:59 ` Stephen Smalley
2015-07-10 7:48 ` Hugh Dickins
2015-07-10 13:09 ` Stephen Smalley
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