Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

memcontrol: ensure memcg acquired by id is properly set up

In the eviction recency check, we attempt to retrieve the memcg to which the folio belonged when it was evicted, by the memcg id stored in the shadow entry. However, there is a chance that the retrieved memcg is not the original memcg that has been killed, but a new one which happens to have the same id.

This is a somewhat unfortunate, but acceptable and rare inaccuracy in the heuristics. However, if we retrieve this new memcg between its allocation and when it is properly attached to the memcg hierarchy, we could run into the following NULL pointer exception during the memcg hierarchy traversal done in mem_cgroup_get_nr_swap_pages():

[ 155757.793456] BUG: kernel NULL pointer dereference, address: 00000000000000c0 [ 155757.807568] #PF: supervisor read access in kernel mode [ 155757.818024] #PF: error_code(0x0000) - not-present page [ 155757.828482] PGD 401f77067 P4D 401f77067 PUD 401f76067 PMD 0 [ 155757.839985] Oops: 0000 [#1] SMP [ 155757.887870] RIP: 0010:mem_cgroup_get_nr_swap_pages+0x3d/0xb0 [ 155757.899377] Code: 29 19 4a 02 48 39 f9 74 63 48 8b 97 c0 00 00 00 48 8b b7 58 02 00 00 48 2b b7 c0 01 00 00 48 39 f0 48 0f 4d c6 48 39 d1 74 42 <48> 8b b2 c0 00 00 00 48 8b ba 58 02 00 00 48 2b ba c0 01 00 00 48 [ 155757.937125] RSP: 0018:ffffc9002ecdfbc8 EFLAGS: 00010286 [ 155757.947755] RAX: 00000000003a3b1c RBX: 000007ffffffffff RCX: ffff888280…