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| author | Hao Ge <gehao@kylinos.cn> | 2025-10-21 09:03:53 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-10-29 14:10:22 +0100 |
| commit | 7c34feda6a9a203c9744281f1b6671b7dad2012d (patch) | |
| tree | 536908b7aeaed66bca4e57fcf0e012cbd6bd2b22 /mm | |
| parent | 2b55b5be1d6cb0cd6f4e50e8a1b3590e366bc33d (diff) | |
| download | linux-7c34feda6a9a203c9744281f1b6671b7dad2012d.tar.gz linux-7c34feda6a9a203c9744281f1b6671b7dad2012d.tar.bz2 linux-7c34feda6a9a203c9744281f1b6671b7dad2012d.zip | |
slab: Avoid race on slab->obj_exts in alloc_slab_obj_exts
commit 6ed8bfd24ce1cb31742b09a3eb557cd008533eec upstream.
If two competing threads enter alloc_slab_obj_exts() and one of them
fails to allocate the object extension vector, it might override the
valid slab->obj_exts allocated by the other thread with
OBJEXTS_ALLOC_FAIL. This will cause the thread that lost this race and
expects a valid pointer to dereference a NULL pointer later on.
Update slab->obj_exts atomically using cmpxchg() to avoid
slab->obj_exts overrides by racing threads.
Thanks for Vlastimil and Suren's help with debugging.
Fixes: f7381b911640 ("slab: mark slab->obj_exts allocation failures unconditionally")
Cc: <stable@vger.kernel.org>
Suggested-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Hao Ge <gehao@kylinos.cn>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Link: https://patch.msgid.link/20251021010353.1187193-1-hao.ge@linux.dev
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/slub.c | 9 |
1 files changed, 6 insertions, 3 deletions
diff --git a/mm/slub.c b/mm/slub.c index 16b5e221c94d..c8022444bd08 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1978,7 +1978,7 @@ static inline void mark_objexts_empty(struct slabobj_ext *obj_exts) static inline void mark_failed_objexts_alloc(struct slab *slab) { - slab->obj_exts = OBJEXTS_ALLOC_FAIL; + cmpxchg(&slab->obj_exts, 0, OBJEXTS_ALLOC_FAIL); } static inline void handle_failed_objexts_alloc(unsigned long obj_exts, @@ -2043,6 +2043,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, #ifdef CONFIG_MEMCG new_exts |= MEMCG_DATA_OBJEXTS; #endif +retry: old_exts = READ_ONCE(slab->obj_exts); handle_failed_objexts_alloc(old_exts, vec, objects); if (new_slab) { @@ -2052,8 +2053,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, * be simply assigned. */ slab->obj_exts = new_exts; - } else if ((old_exts & ~OBJEXTS_FLAGS_MASK) || - cmpxchg(&slab->obj_exts, old_exts, new_exts) != old_exts) { + } else if (old_exts & ~OBJEXTS_FLAGS_MASK) { /* * If the slab is already in use, somebody can allocate and * assign slabobj_exts in parallel. In this case the existing @@ -2062,6 +2062,9 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, mark_objexts_empty(vec); kfree(vec); return 0; + } else if (cmpxchg(&slab->obj_exts, old_exts, new_exts) != old_exts) { + /* Retry if a racing thread changed slab->obj_exts from under us. */ + goto retry; } kmemleak_not_leak(vec); |