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

[Shoaib Rao]

On 9/5/2024 12:46 PM, Kuniyuki Iwashima wrote:
> 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://urldefense.com/v3/__https://lore.kernel.org/netdev/20240905193240.17565-5-kuniyu@xxxxxxxxxx/__;!!ACWV5N9M2RV99hQ!IJeFvLdaXIRN2ABsMFVaKOEjI3oZb2kUr6ld6ZRJCPAVum4vuyyYwUP6_5ZH9mGZiJDn6vrbxBAOqYI$

Thanks that is great. Isn't EFAULT,  normally indicative of an issue 
with the user provided address of the buffer, not the kernel buffer.

Shoaib