smb: client: split cached_fid bitfields to avoid shared-byte RMW races

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commit ec306600d5 upstream.

is_open, has_lease and on_list are stored in the same bitfield byte in
struct cached_fid but are updated in different code paths that may run
concurrently. Bitfield assignments generate byte read–modify–write
operations (e.g. `orb $mask, addr` on x86_64), so updating one flag can
restore stale values of the others.

A possible interleaving is:
    CPU1: load old byte (has_lease=1, on_list=1)
    CPU2: clear both flags (store 0)
    CPU1: RMW store (old | IS_OPEN) -> reintroduces cleared bits

To avoid this class of races, convert these flags to separate bool
fields.

Cc: stable@vger.kernel.org
Fixes: ebe98f1447 ("cifs: enable caching of directories for which a lease is held")
Signed-off-by: Henrique Carvalho <henrique.carvalho@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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Henrique Carvalho 2026-01-27 13:01:28 -03:00 • committed by Greg Kroah-Hartman

parent 81ea0ab0c0

commit 4cfa4c37dc

1 changed files with 4 additions and 4 deletions

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fs/smb/client/cached_dir.h

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