smb: client: fix data corruption with concurrent writes and O_TRUNC

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cifs_do_truncate() flushes dirty pages with filemap_write_and_wait()
and truncates the file on the server, but in the old code both
operations ran without holding i_rwsem or invalidate_lock.  A
concurrent buffered write via netfs_perform_write() -- which only
needs i_rwsem shared -- could dirty new pages after the flush but
before the local truncation, and those pages would be silently
discarded by cifs_setsize() -> truncate_pagecache().

Fix by acquiring inode_lock (exclusive i_rwsem) and
filemap_invalidate_lock at the top of cifs_do_truncate(), so the
entire flush-truncate-resize sequence is atomic with respect to:

  - buffered writes (blocked by exclusive i_rwsem, since
    netfs_start_io_write takes i_rwsem shared),
  - read page faults (blocked by exclusive invalidate_lock, since
    filemap_fault takes it shared),
  - writeback collection (blocked by netfs_wb_begin/netfs_wb_end
    around the server truncate and local resize, since
    netfs_writepages also acquires the wb lock).

Fixes: 110fee6b9b ("smb: client: fix missing timestamp updates with O_TRUNC")
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

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This commit is contained in:

Paulo Alcantara 2026-08-28 19:08:09 -03:00

parent fe39cd9d48

commit a8603b52b3

1 changed files with 18 additions and 10 deletions

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fs/smb/client/file.c

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