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

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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>
This commit is contained in:
Henrique Carvalho 2026-01-27 13:01:28 -03:00 committed by Steve French
parent 96c4af4185
commit ec306600d5
1 changed files with 4 additions and 4 deletions
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8
fs/smb/client/cached_dir.h
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@ -36,10 +36,10 @@ struct cached_fid {
struct list_head entry;
struct cached_fids *cfids;
const char *path;
bool has_lease:1;
bool is_open:1;
bool on_list:1;
bool file_all_info_is_valid:1;
bool has_lease;
bool is_open;
bool on_list;
bool file_all_info_is_valid;
unsigned long time; /* jiffies of when lease was taken */
unsigned long last_access_time; /* jiffies of when last accessed */
struct kref refcount;