Description

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

af_unix: Call kfree_skb() for dead unix_(sk)->oob_skb in GC.

syzbot reported a warning [0] in __unix_gc() with a repro, which
creates a socketpair and sends one socket's fd to itself using the
peer.

socketpair(AF_UNIX, SOCK_STREAM, 0, [3, 4]) = 0
sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="\360", iov_len=1}],
msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET,
cmsg_type=SCM_RIGHTS, cmsg_data=[3]}],
msg_controllen=24, msg_flags=0}, MSG_OOB|MSG_PROBE|MSG_DONTWAIT|MSG_ZEROCOPY) = 1

This forms a self-cyclic reference that GC should finally untangle
but does not due to lack of MSG_OOB handling, resulting in memory
leak.

Recently, commit 11498715f266 ("af_unix: Remove io_uring code for
GC.") removed io_uring's dead code in GC and revealed the problem.

The code was executed at the final stage of GC and unconditionally
moved all GC candidates from gc_candidates to gc_inflight_list.
That papered over the reported problem by always making the following
WARN_ON_ONCE(!list_empty(&gc_candidates)) false.

The problem has been there since commit 2aab4b969002 ("af_unix: fix
struct pid leaks in OOB support") added full scm support for MSG_OOB
while fixing another bug.

To fix this problem, we must call kfree_skb() for unix_sk(sk)->oob_skb
if the socket still exists in gc_candidates after purging collected skb.

Then, we need t...

Classification

CVE ID: CVE-2024-26676

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.05% (probability of being exploited)

EPSS Percentile: 17.81% (scored less or equal to compared to others)

EPSS Date: 2025-02-03 (when was this score calculated)

References

https://git.kernel.org/stable/c/4fe505c63aa3273135a57597fda761e9aecc7668
https://git.kernel.org/stable/c/e0e09186d8821ad59806115d347ea32efa43ca4b
https://git.kernel.org/stable/c/b74aa9ce13d02b7fd37c5325b99854f91b9b4276
https://git.kernel.org/stable/c/82ae47c5c3a6b27fdc0f9e83c1499cb439c56140
https://git.kernel.org/stable/c/1279f9d9dec2d7462823a18c29ad61359e0a007d

Timeline