Re: [syzbot] [net?] KASAN: slab-use-after-free Read in unix_stream_read_actor (2)

[Kuniyuki Iwashima]

From: Shoaib Rao <rao.shoaib@xxxxxxxxxx>
Date: Thu, 5 Sep 2024 00:35:35 -0700
> Hi All,
> 
> I am not able to reproduce the issue. I have run the C program at least 
> 100 times in a loop. In the I do get an EFAULT, not sure if that is 
> intentional or not but no panic. Should I be doing something 
> differently? The kernel version I am using is 
> v6.11-rc6-70-gc763c4339688. Later I can try with the exact version.

The -EFAULT is the bug meaning that we were trying to read an consumed skb.

But the first bug is in recvfrom() that shouldn't be able to read OOB skb
without MSG_OOB, which doesn't clear unix_sk(sk)->oob_skb, and later
something bad happens.

  socketpair(AF_UNIX, SOCK_STREAM, 0, [3, 4]) = 0
  sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="\333", iov_len=1}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, MSG_OOB|MSG_DONTWAIT) = 1
  recvmsg(3, {msg_name=NULL, msg_namelen=0, msg_iov=NULL, msg_iovlen=0, msg_controllen=0, msg_flags=MSG_OOB}, MSG_OOB|MSG_WAITFORONE) = 1
  sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="\21", iov_len=1}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, MSG_OOB|MSG_NOSIGNAL|MSG_MORE) = 1
> recvfrom(3, "\21", 125, MSG_DONTROUTE|MSG_TRUNC|MSG_DONTWAIT, NULL, NULL) = 1
  recvmsg(3, {msg_namelen=0}, MSG_OOB|MSG_ERRQUEUE) = -1 EFAULT (Bad address)

I posted a fix officially:
https://lore.kernel.org/netdev/20240905193240.17565-5-kuniyu@xxxxxxxxxx/