CVE-2026-97985af_unix: Update last skb marker in manage_oob().

Official description

In the Linux kernel, the following vulnerability has been resolved: af_unix: Update last skb marker in manage_oob(). Fahad Alharbi reported that blocking recv(MSG_PEEK) could hog CPU due to OOB skb. In the following cases, manage_oob() skips OOB skb(s) and returns NULL for the last recv(MSG_PEEK): socketpair(AF_UNIX, SOCK_STREAM, 0, sk); 1) skb -> OOB skb -> NULL send(sk[0], "ab", 2, MSG_OOB); recv(sk[1], buf, 0, MSG_PEEK); 2) skb -> consumed OOB skb -> NULL send(sk[0], "ab", 2, MSG_OOB); recv(sk[1], buf, 1, MSG_OOB); recv(sk[1], buf, 0, MSG_PEEK); 3) consumed OOB skb -> OOB skb -> NULL send(sk[0], "a", 1, MSG_OOB); recv(sk[1], buf, 0, MSG_OOB); send(sk[0], "b", 1, MSG_OOB); recv(sk[1], buf, 1, MSG_PEEK); Then, @copied is 0 in unix_stream_read_generic() (zero-length buffer, or non-OOB skb is not yet consumed), and unix_stream_data_wait() is called. However, it returns immediately because @last is not updated in unix_stream_read_generic(), and the thread busy-waits for a new skb. Let's update @last in manage_oob(). For MSG_PEEK, @last is updated with the skipped OOB, and for the non-peek case, @last matches the returned value (when !copied) because OOB is unlinked. Note that manage_oob() is inlined and no stack canary is added.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/bd91dc313afe21e9d6b31ca6a47606a33ca5e35c
• https://git.kernel.org/stable/c/0630bfc773d85ac44da05b2c5a037dbbd39301ab
• https://git.kernel.org/stable/c/f1816b3d7ce80dcf086bb68ff5ae6e09520ca1fa
• https://git.kernel.org/stable/c/fc62a26493a98a0424d9dae2eb92a1daa1321f65
• https://git.kernel.org/stable/c/94fd4debd2e3a69cf93e766c8b328a810c228119