Re: [PATCH 10/11] ksmbd: remove setattr preparations in set_file_basic_info()

[Namjae Jeon <linkinjeon@kernel.org>]

2021-10-02 3:51 GMT+09:00, Marios Makassikis <mmakassikis@freebox.fr>:
> On Mon, 2021-08-23 at 17:13 +0200, Christian Brauner wrote:
>> From: Christian Brauner <christian.brauner@ubuntu.com>
>>
>> Permission checking and copying over ownership information is the
>> task
>> of the underlying filesystem not ksmbd. The order is also wrong here.
>> This modifies the inode before notify_change(). If notify_change()
>> fails
>> this will have changed ownership nonetheless. All of this is
>> unnecessary
>> though since the underlying filesystem's ->setattr handler will do
>> all
>> this (if required) by itself.
>> Cc: Steve French <stfrench@microsoft.com>
>> Cc: Christoph Hellwig <hch@infradead.org>
>> Cc: Namjae Jeon <namjae.jeon@samsung.com>
>> Cc: Hyunchul Lee <hyc.lee@gmail.com>
>> Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
>> Cc: linux-cifs@vger.kernel.org
>> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
>> ---
>>  fs/ksmbd/smb2pdu.c | 5 -----
>>  1 file changed, 5 deletions(-)
>>
>> diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
>> index 1148e52a4037..059764753aaa 100644
>> --- a/fs/ksmbd/smb2pdu.c
>> +++ b/fs/ksmbd/smb2pdu.c
>> @@ -5521,12 +5521,7 @@ static int set_file_basic_info(struct
>> ksmbd_file *fp, char *buf,
>>  		if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
>>  			return -EACCES;
>>
>> -		rc = setattr_prepare(user_ns, dentry, &attrs);
>> -		if (rc)
>> -			return -EINVAL;
>> -
>>  		inode_lock(inode);
>> -		setattr_copy(user_ns, inode, &attrs);
>>  		attrs.ia_valid &= ~ATTR_CTIME;
>>  		rc = notify_change(user_ns, dentry, &attrs, NULL);
>>  		inode_unlock(inode);
>
> Hello,
Hi Marios,
>
> With this change, rsync'ing a large directory (kernel repo checkout for
> example) to a FUSE-backed share crashes the kernel:
>
>  BUG: unable to handle page fault for address: fffffffffffffff8
>  #PF: supervisor write access in kernel mode
>  #PF: error_code(0x0002) - not-present page
>  PGD 3229067 P4D 3229067 PUD 322b067 PMD 0
>  Oops: 0002 [#1] SMP KASAN NOPTI
>  CPU: 0 PID: 55 Comm: kworker/u2:1 Not tainted 5.15.0-rc3+ #186
>  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-
> 1ubuntu1.1 04/01/2014
>  Workqueue: writeback wb_workfn (flush-8:17-fuseblk)
>  RIP: 0010:fuse_file_get+0x26/0x50
>  Code: 00 0f 1f 00 0f 1f 44 00 00 41 56 53 48 89 fb 4c 8d 77 28 4c 89
> f7 be 04 00 00 00 e8 54 ad c1 ff be 01 00 00 00 b8 01 00 e
>  RSP: 0018:ffffc900001af660 EFLAGS: 00010256
>  RAX: 0000000000000001 RBX: ffffffffffffffd0 RCX: ffffffff818314cc
>  RDX: 0000000000000001 RSI: 0000000000000001 RDI: fffffffffffffff8
>  RBP: ffff8880108b0680 R08: dffffc0000000000 R09: fffffc0000000000
>  R10: fffffc0000000000 R11: 0000000000000000 R12: 0000000000000000
>  R13: 0000000000020087 R14: fffffffffffffff8 R15: ffff8880108b0680
>  FS:  0000000000000000(0000) GS:ffff888036200000(0000)
> knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: fffffffffffffff8 CR3: 00000000101a4000 CR4: 00000000000006f0
>  Call Trace:
>   __fuse_write_file_get+0x4e/0x70
>   fuse_write_inode+0xf/0x40
>   __writeback_single_inode+0x206/0x250
>   writeback_sb_inodes+0x3fb/0x760
>   ? queue_io+0xd0/0xd0
>   ? trylock_super+0x17/0x60
>   ? __init_rwsem+0xf0/0xf0
>   ? rcu_read_lock_sched_held+0xa5/0x130
>   ? __bpf_trace_rcu_barrier+0x10/0x10
>   ? do_raw_spin_lock+0x14f/0x250
>   ? __bpf_trace_rcu_barrier+0x10/0x10
>   __writeback_inodes_wb+0xbf/0x130
>   wb_writeback+0x25b/0x360
>   ? print_irqtrace_events+0x110/0x110
>   ? trace_writeback_exec+0x150/0x150
>   ? _local_bh_enable+0x70/0x70
>   ? cpumask_next+0x20/0x50
>   ? cpumask_next+0x20/0x50
>   wb_workfn+0x608/0x860
>   ? __inode_wait_for_writeback+0x1c0/0x1c0
>   ? check_chain_key+0x1cf/0x2a0
>   ? __lock_acquire+0x9f4/0xdf0
>   ? lock_acquire+0x14d/0x370
>   ? process_one_work+0x2c5/0x550
>   ? lock_acquire+0x176/0x370
>   ? rcu_read_lock_sched_held+0xa5/0x130
>   ? __bpf_trace_rcu_barrier+0x10/0x10
>   ? lock_acquire+0x14d/0x370
>   ? worker_thread+0xf8/0x4a0
>   ? lock_acquire+0x176/0x370
>   process_one_work+0x304/0x550
>   ? worker_detach_from_pool+0x100/0x100
>   ? _raw_spin_lock_irq+0xaf/0xe0
>   ? _raw_spin_lock_irqsave+0xf0/0xf0
>   ? __list_add_valid+0x2a/0xa0
>   worker_thread+0x373/0x4a0
>   kthread+0x1d9/0x1f0
>   ? pr_cont_work+0xa0/0xa0
>   ? __list_add+0x50/0x50
>   ret_from_fork+0x1f/0x30
>  Modules linked in:
>  CR2: fffffffffffffff8
>  ---[ end trace fa4a96caf17482dd ]---
>
> $ ./scripts/faddr2line vmlinux.o fuse_file_get+0x26/0x50
> fuse_file_get+0x26/0x50:
> arch_atomic_fetch_add at arch/x86/include/asm/atomic.h:184
> (inlined by) atomic_fetch_add_relaxed at include/asm-generic/atomic-
> instrumented.h:143
> (inlined by) __refcount_add at include/linux/refcount.h:193
> (inlined by) __refcount_inc at include/linux/refcount.h:250
> (inlined by) refcount_inc at include/linux/refcount.h:267
> (inlined by) fuse_file_get at fs/fuse/file.c:93
>
> $ ./scripts/faddr2line vmlinux.o __fuse_write_file_get+0x4e/0x70
> __fuse_write_file_get+0x4e/0x70:
> __fuse_write_file_get at fs/fuse/file.c:1827
>
> I had already encountered this before [0]. Back then, changing ksmbd to
> use notify_change rather than mark_inode_dirty fixed the issue [1].
>
> Using ext4/xfs does not trigger the bug.
Thanks for your report and detailed check.
>
> rsync'ing the same folder over SMB (with samba4), or over NFS does not
> trigger the bug either. The only combination where I'm seeing this so
> far is ksmbd+FUSE, although I can't tell if it's a bug in ksmbd side or
> FUSE.

Could you please check your issue is fixed with the following change ?

diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
index 4d1be224dd8e..e58a5a99d6ed 100644
--- a/fs/ksmbd/smb2pdu.c
+++ b/fs/ksmbd/smb2pdu.c
@@ -5483,7 +5483,6 @@ static int set_file_basic_info(struct ksmbd_file *fp,
 			       struct ksmbd_share_config *share)
 {
 	struct iattr attrs;
-	struct timespec64 ctime;
 	struct file *filp;
 	struct inode *inode;
 	struct user_namespace *user_ns;
@@ -5505,13 +5504,11 @@ static int set_file_basic_info(struct ksmbd_file *fp,
 		attrs.ia_valid |= (ATTR_ATIME | ATTR_ATIME_SET);
 	}

+	attrs.ia_valid |= ATTR_CTIME;
 	if (file_info->ChangeTime) {
 		attrs.ia_ctime = ksmbd_NTtimeToUnix(file_info->ChangeTime);
-		ctime = attrs.ia_ctime;
-		attrs.ia_valid |= ATTR_CTIME;
-	} else {
-		ctime = inode->i_ctime;
-	}
+	} else
+		attrs.ia_ctime = inode->i_ctime;

 	if (file_info->LastWriteTime) {
 		attrs.ia_mtime = ksmbd_NTtimeToUnix(file_info->LastWriteTime);
@@ -5557,11 +5554,9 @@ static int set_file_basic_info(struct ksmbd_file *fp,
 			return -EACCES;

 		inode_lock(inode);
+		inode->i_ctime = attrs.ia_ctime;
+		attrs.ia_valid &= ~ATTR_CTIME;
 		rc = notify_change(user_ns, dentry, &attrs, NULL);
-		if (!rc) {
-			inode->i_ctime = ctime;
-			mark_inode_dirty(inode);
-		}
 		inode_unlock(inode);
 	}
 	return rc;
-- 
2.25.1

>
> Marios
>
> [0]
> https://lore.kernel.org/linux-fsdevel/CAF6XXKWCwqSa72p+iQjg4QSBmAkX4Y5DxGrRR1tW1ar2uthd=w@mail.gmail.com/T/#u
> [1]
> https://github.com/cifsd-team/ksmbd/commit/5e929125e519acaf48abc4c42f8389caa26c4d5a#diff-9f95c7d87d27c50e4e1d0afb24772b60bfa1449d619c118f23d7a2493d3ea9b0
>
>