CVE-2023-53136

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

af_unix: fix struct pid leaks in OOB support

syzbot reported struct pid leak [1].

Issue is that queue_oob() calls maybe_add_creds() which potentially holds a reference on a pid.

But skb->destructor is not set (either directly or by calling unix_scm_to_skb())

This means that subsequent kfree_skb() or consume_skb() would leak this reference.

In this fix, I chose to fully support scm even for the OOB message.

[1] BUG: memory leak unreferenced object 0xffff8881053e7f80 (size 128): comm "syz-executor242", pid 5066, jiffies 4294946079 (age 13.220s) hex dump (first 32 bytes): 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ backtrace: [<ffffffff812ae26a>] alloc_pid+0x6a/0x560 kernel/pid.c:180 [<ffffffff812718df>] copy_process+0x169f/0x26c0 kernel/fork.c:2285 [<ffffffff81272b37>] kernel_clone+0xf7/0x610 kernel/fork.c:2684 [<ffffffff812730cc>] __do_sys_clone+0x7c/0xb0 kernel/fork.c:2825 [<ffffffff849ad699>] do_syscall_x64 arch/x86/entry/common.c:50 [inline] [<ffffffff849ad699>] do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80 [<ffffffff84a0008b>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

A memory leak in the AF_UNIX OOB message handling was fixed in queue_oob(). When SCM credentials were attached to an OOB message, a missing call to unix_scm_to_skb() resulted in leaked struct pid references, as skb->destructor was not set. The issue was reported by Syzbot and required a process to send OOB messages with SCM credentials. Local attackers with the ability to create UNIX domain sockets and send OOB messages can trigger a kernel memory leak.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.