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Message-ID: <19ce4e18-f1e0-44c4-b006-83001eb6ae24@oracle.com> Date: Thu, 5 Sep 2024 13:48:16 -0700 From: Shoaib Rao <rao.shoaib@...cle.com> To: Kuniyuki Iwashima <kuniyu@...zon.com> Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, 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) On 9/5/2024 1:35 PM, Kuniyuki Iwashima wrote: > 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. No it did not work. As soon as KASAN detected read after free it should have paniced as it did in the report and I have been running the syzbot's C program in a continuous loop. I would like to reproduce the issue before we can accept the fix -- If that is alright with you. I will try your new test case later and report back. Thanks for the patch though. Regards, Shoaib
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