Linux Kernel up to 7.2.6/7.3-rc2 Slab Allocator mm/slab __slab_try_return_freelist list_lock race condition

Summaryinfo

A vulnerability, which was classified as very critical, has been found in Linux Kernel up to 7.2.6/7.3-rc2. The impacted element is the function __slab_try_return_freelist of the file mm/slab of the component Slab Allocator. This manipulation of the argument list_lock causes race condition. This vulnerability is handled as CVE-2026-97941. The attack can be initiated remotely. There is not any exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability classified as very critical was found in Linux Kernel up to 7.2.6/7.3-rc2. Affected by this vulnerability is the function __slab_try_return_freelist of the file mm/slab of the component Slab Allocator. The manipulation of the argument list_lock with an unknown input leads to a race condition vulnerability. The CWE definition for the vulnerability is CWE-362. The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: mm/slab: take n->list_lock in __slab_try_return_freelist() to avoid race Commit ba7425312607 ("mm, slab: add an optimistic __slab_try_return_freelist()") incorrectly assumed that nobody has freed an object to the slab as long as slab->freelist is NULL and cmpxchg succeeds. However, as reported by Hyunwoo Kim [1], other CPUs might have freed an object to the slab, insert the slab to the partial list, then allocated an object from the slab, and be in the middle of removing the slab from the list under n->list_lock. Since __refill_objects_node() puts the slab back on pc.slabs outside n->list_lock, it might insert the slab into that list while the slab is concurrently being removed from n->partial. This led to a list corruption [1]: list_add corruption. next->prev should be prev (ffff888100000248), but was dead000000000122. (next=ffffea000416e410). kernel BUG at lib/list_debug.c:29! Oops: invalid opcode: 0000 [#1] SMP NOPTI CPU: 1 UID: 65534 PID: 144 Comm: poc Not tainted 7.2.0-16172-gcf72cbb39da8-dirty #1 PREEMPT(lazy) RIP: 0010:__list_add_valid_or_report+0x80/0xd0 ... Call Trace: alloc_from_new_slab+0x183/0x300 ___slab_alloc+0x31c/0x890 __kmalloc_noprof+0x3d4/0x800 lsm_blob_alloc+0x2d/0x50 security_msg_msg_alloc+0x26/0x90 load_msg+0x1aa/0x210 do_msgsnd+0x91/0x800 do_syscall_64+0x109/0x5d0 entry_SYSCALL_64_after_hwframe+0x77/0x7f ... Kernel panic - not syncing: Fatal exception This is a classic ABA problem where cmpxchg succeeds but the state has changed since __refill_objects_node() took the freelist from the slab. As Vlastimil Babka mentioned [2], it should be rare to return more than one slab (due to the racy read of slab->counters in get_partial_node_bulk()). Therefore, instead of introducing additional complexity, acquire and release n->list_lock twice in the worst case. Return the slab directly to the partial list and hold n->list_lock across the cmpxchg and add_partial(). This is similar to the initial version of commit ba7425312607 [3]. This is enough to avoid the race as the list manipulation is serialized by n->list_lock. While at it, bring back unlikely() hint now that the condition is unlikely.

It is possible to read the advisory at git.kernel.org. This vulnerability is known as CVE-2026-97941 since 09/25/2026. The exploitation appears to be easy. The attack can be launched remotely. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/25/2026).

Upgrading to version 7.2.7 or 7.3-rc3 eliminates this vulnerability. Applying the patch 570a6aaf6b52c6ec098f4811cdb52b1496f13d15/4a724bcf5d703e18957397914d79156fa2cf1174 is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.5
• 7.2.6
• 7.3-rc1
• 7.3-rc2

License

• open-source

Website

• Vendor: https://www.kernel.org/

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