diff options
| author | Jose Fernandez (Anthropic) <jose.fernandez@linux.dev> | 2026-05-04 12:55:17 +0000 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2026-05-28 21:30:13 -0700 |
| commit | 9d618e20c4abafb8cf35fea0f344c94e801f67e0 (patch) | |
| tree | 06c48a9d14cc8b322d914f5f2aba50c8f7006f01 /mm | |
| parent | 78adf36286c2dd6bb4b85f5419bc49f3d78a2fda (diff) | |
| download | linux-next-history-9d618e20c4abafb8cf35fea0f344c94e801f67e0.tar.gz | |
mm: swap_cgroup: fix NULL deref in lookup_swap_cgroup_id on swapless host
lookup_swap_cgroup_id() passes swap_cgroup_ctrl[type].map to
__swap_cgroup_id_lookup() without checking that the type was ever
registered via swap_cgroup_swapon(). On a swapless host every ctrl->map
is NULL, so __swap_cgroup_id_lookup() dereferences NULL + a scaled
swp_offset().
Since commit bea67dcc5eea ("mm: attempt to batch free swap entries for
zap_pte_range()"), zap_pte_range() -> swap_pte_batch() calls
lookup_swap_cgroup_id() on any non-present, non-none PTE that decodes as a
real swap entry, without first validating it against swap_info[]. A
single PTE corrupted into a type-0 swap entry takes the host down at
process exit.
We hit this in production on a swapless 6.12.58 host: ~1s of
"get_swap_device: Bad swap file entry 3f800204222bb" (do_swap_page() being
correctly defensive about the same entry) followed by
BUG: unable to handle page fault for address: 000003f800204220
RIP: 0010:lookup_swap_cgroup_id+0x2b/0x60
Call Trace:
swap_pte_batch+0xbf/0x230
zap_pte_range+0x4c8/0x780
unmap_page_range+0x190/0x3e0
exit_mmap+0xd9/0x3c0
do_exit+0x20c/0x4b0
syzbot has reported the identical stack.
The source of the PTE corruption is a separate bug; this change makes the
teardown path as robust as the fault path already is. Every other caller
of lookup_swap_cgroup_id() is downstream of a get_swap_device() that has
already validated the entry, so the new branch is cold.
Link: https://lore.kernel.org/20260504-swap-cgroup-fix-7-0-v1-1-f53ff41ee553@linux.dev
Fixes: bea67dcc5eea ("mm: attempt to batch free swap entries for zap_pte_range()")
Signed-off-by: Jose Fernandez (Anthropic) <jose.fernandez@linux.dev>
Reported-by: syzbot+e12bd9ca48157add237a@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/69859728.050a0220.3b3015.0033.GAE@google.com
Assisted-by: Claude:unspecified
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/swap_cgroup.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/mm/swap_cgroup.c b/mm/swap_cgroup.c index de779fed8c210..95c38e54dd587 100644 --- a/mm/swap_cgroup.c +++ b/mm/swap_cgroup.c @@ -124,6 +124,8 @@ unsigned short lookup_swap_cgroup_id(swp_entry_t ent) return 0; ctrl = &swap_cgroup_ctrl[swp_type(ent)]; + if (unlikely(!ctrl->map)) + return 0; return __swap_cgroup_id_lookup(ctrl->map, swp_offset(ent)); } |