CVE-2024-26676

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> af_unix: Call kfree_skb() for dead unix_(sk)-&gt;oob_skb in GC.<br /> <br /> syzbot reported a warning [0] in __unix_gc() with a repro, which<br /> creates a socketpair and sends one socket&amp;#39;s fd to itself using the<br /> peer.<br /> <br /> socketpair(AF_UNIX, SOCK_STREAM, 0, [3, 4]) = 0<br /> sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="\360", iov_len=1}],<br /> msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET,<br /> cmsg_type=SCM_RIGHTS, cmsg_data=[3]}],<br /> msg_controllen=24, msg_flags=0}, MSG_OOB|MSG_PROBE|MSG_DONTWAIT|MSG_ZEROCOPY) = 1<br /> <br /> This forms a self-cyclic reference that GC should finally untangle<br /> but does not due to lack of MSG_OOB handling, resulting in memory<br /> leak.<br /> <br /> Recently, commit 11498715f266 ("af_unix: Remove io_uring code for<br /> GC.") removed io_uring&amp;#39;s dead code in GC and revealed the problem.<br /> <br /> The code was executed at the final stage of GC and unconditionally<br /> moved all GC candidates from gc_candidates to gc_inflight_list.<br /> That papered over the reported problem by always making the following<br /> WARN_ON_ONCE(!list_empty(&amp;gc_candidates)) false.<br /> <br /> The problem has been there since commit 2aab4b969002 ("af_unix: fix<br /> struct pid leaks in OOB support") added full scm support for MSG_OOB<br /> while fixing another bug.<br /> <br /> To fix this problem, we must call kfree_skb() for unix_sk(sk)-&gt;oob_skb<br /> if the socket still exists in gc_candidates after purging collected skb.<br /> <br /> Then, we need to set NULL to oob_skb before calling kfree_skb() because<br /> it calls last fput() and triggers unix_release_sock(), where we call<br /> duplicate kfree_skb(u-&gt;oob_skb) if not NULL.<br /> <br /> Note that the leaked socket remained being linked to a global list, so<br /> kmemleak also could not detect it. We need to check /proc/net/protocol<br /> to notice the unfreed socket.<br /> <br /> [0]:<br /> WARNING: CPU: 0 PID: 2863 at net/unix/garbage.c:345 __unix_gc+0xc74/0xe80 net/unix/garbage.c:345<br /> Modules linked in:<br /> CPU: 0 PID: 2863 Comm: kworker/u4:11 Not tainted 6.8.0-rc1-syzkaller-00583-g1701940b1a02 #0<br /> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024<br /> Workqueue: events_unbound __unix_gc<br /> RIP: 0010:__unix_gc+0xc74/0xe80 net/unix/garbage.c:345<br /> Code: 8b 5c 24 50 e9 86 f8 ff ff e8 f8 e4 22 f8 31 d2 48 c7 c6 30 6a 69 89 4c 89 ef e8 97 ef ff ff e9 80 f9 ff ff e8 dd e4 22 f8 90 0b 90 e9 7b fd ff ff 48 89 df e8 5c e7 7c f8 e9 d3 f8 ff ff e8<br /> RSP: 0018:ffffc9000b03fba0 EFLAGS: 00010293<br /> RAX: 0000000000000000 RBX: ffffc9000b03fc10 RCX: ffffffff816c493e<br /> RDX: ffff88802c02d940 RSI: ffffffff896982f3 RDI: ffffc9000b03fb30<br /> RBP: ffffc9000b03fce0 R08: 0000000000000001 R09: fffff52001607f66<br /> R10: 0000000000000003 R11: 0000000000000002 R12: dffffc0000000000<br /> R13: ffffc9000b03fc10 R14: ffffc9000b03fc10 R15: 0000000000000001<br /> FS: 0000000000000000(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000<br /> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033<br /> CR2: 00005559c8677a60 CR3: 000000000d57a000 CR4: 00000000003506f0<br /> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000<br /> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400<br /> Call Trace:<br /> <br /> process_one_work+0x889/0x15e0 kernel/workqueue.c:2633<br /> process_scheduled_works kernel/workqueue.c:2706 [inline]<br /> worker_thread+0x8b9/0x12a0 kernel/workqueue.c:2787<br /> kthread+0x2c6/0x3b0 kernel/kthread.c:388<br /> ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147<br /> ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:242<br />