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 13:37:06 -0700
> On 9/5/2024 1:15 PM, Shoaib Rao wrote:
> >
> > 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
> >
> Can you provide the full test case that you used to reproduce the issue.

I used the syzbot's repro, but you can check a new test case added
in my patch.