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Message-ID: <c45d66d7-64fc-4fa8-8c38-ab2e9ca65635@oracle.com> Date: Fri, 6 Sep 2024 09:48:02 -0700 From: Shoaib Rao <rao.shoaib@...cle.com> To: Eric Dumazet <edumazet@...gle.com> Cc: Kuniyuki Iwashima <kuniyu@...zon.com>, davem@...emloft.net, 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 9/6/2024 5:37 AM, Eric Dumazet wrote: > On Thu, Sep 5, 2024 at 10:48 PM Shoaib Rao <rao.shoaib@...cle.com> wrote: >> >> 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. > KASAN does not panic unless you request it. > > Documentation/dev-tools/kasan.rst > > KASAN is affected by the generic ``panic_on_warn`` command line parameter. > When it is enabled, KASAN panics the kernel after printing a bug report. > > By default, KASAN prints a bug report only for the first invalid memory access. > With ``kasan_multi_shot``, KASAN prints a report on every invalid access. This > effectively disables ``panic_on_warn`` for KASAN reports. > > Alternatively, independent of ``panic_on_warn``, the ``kasan.fault=`` boot > parameter can be used to control panic and reporting behaviour: > > - ``kasan.fault=report``, ``=panic``, or ``=panic_on_write`` controls whether > to only print a KASAN report, panic the kernel, or panic the kernel on > invalid writes only (default: ``report``). The panic happens even if > ``kasan_multi_shot`` is enabled. Note that when using asynchronous mode of > Hardware Tag-Based KASAN, ``kasan.fault=panic_on_write`` always panics on > asynchronously checked accesses (including reads). Hi Eric, Thanks for the update. I forgot to mention that I I did set /proc/sys/kernel/panic_on_warn to 1. I ran the program over night in two separate windows, there are no reports and no panic. I first try to reproduce the issue, because if I can not, how can I be sure that I have fixed that bug? I may find another issue and fix it but not the one that I was trying to. Please be assured that I am not done, I continue to investigate the issue. If someone has a way of reproducing the failure please kindly let me know. Kind regards, Shoaib
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