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Message-ID: <d7073535-b435-418e-a58f-46728fc79c1e@oracle.com> Date: Thu, 5 Sep 2024 13:41:26 -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 1:37 PM, Shoaib Rao wrote: > > 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@...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. >> >> Shoaib >> > Can you provide the full test case that you used to reproduce the issue. > > Thanks, > > Shoaib > > From the recvmsg man page Return Value These calls return the number of bytes received, or -1 if an error occurred. The return value will be 0 when the peer has performed an orderly shutdown. *EFAULT* The receive buffer*pointer*(s) point outside the process's address space. I still do not understand why if I had all the check on and the issue occured, why the kernel did not panic. Maybe, running the exact test case will help me understand. Shoaib
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