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Message-ID: <20240905203525.26121-1-kuniyu@amazon.com> Date: Thu, 5 Sep 2024 13:35:25 -0700 From: Kuniyuki Iwashima <kuniyu@...zon.com> To: <rao.shoaib@...cle.com> CC: <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>, <kuniyu@...zon.com>, <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>, <pabeni@...hat.com>, <syzbot+8811381d455e3e9ec788@...kaller.appspotmail.com>, <syzkaller-bugs@...glegroups.com> Subject: Re: [syzbot] [net?] KASAN: slab-use-after-free Read in unix_stream_read_actor (2) From: Shoaib Rao <rao.shoaib@...cle.com> Date: Thu, 5 Sep 2024 13:15:18 -0700 > On 9/5/2024 12:46 PM, Kuniyuki Iwashima wrote: > > From: Shoaib Rao <rao.shoaib@...cle.com> > > 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@amazon.com/__;!!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. Normally, it's used when copy_to_user() or copy_from_user() or something similar failed. But this time, if you turn KASAN off, you'll see the last recvmsg() returns 1-byte garbage instead of -EFAULT, so actually KASAN worked on your host, I guess.
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