Re: [syzbot] [net?] KASAN: slab-use-after-free Read in unix_stream_read_actor (2)

[Shoaib Rao]

On 9/6/2024 9:48 AM, Shoaib Rao wrote:
> On 9/6/2024 5:37 AM, Eric Dumazet wrote:
> > On Thu, Sep 5, 2024 at 10:48 PM Shoaib Rao <rao.shoaib@xxxxxxxxxx> 
> > wrote:
> > > On 9/5/2024 1:35 PM, Kuniyuki Iwashima wrote:
> > > > From: Shoaib Rao <rao.shoaib@xxxxxxxxxx>
> > > > Date: Thu, 5 Sep 2024 13:15:18 -0700
> > > > > 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.
> > > > 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
I have tried reproducing using the newly added tests but no luck. I will 
keep trying but if there is another occurrence please let me know. I am 
using an AMD system but that should not have any impact.

Shoaib

[root@turbo-2 af_unix]# git diff msg_oob.c
diff --git a/tools/testing/selftests/net/af_unix/msg_oob.c 
b/tools/testing/selftests/net/af_unix/msg_oob.c
index 535eb2c3d7d1..5fedb55adcf2 100644
--- a/tools/testing/selftests/net/af_unix/msg_oob.c
+++ b/tools/testing/selftests/net/af_unix/msg_oob.c
@@ -525,6 +525,30 @@ TEST_F(msg_oob, ex_oob_drop_2)
      }
 }
+TEST_F(msg_oob, ex_oob_oob)
+{
+       sendpair("x", 1, MSG_OOB);
+       epollpair(true);
+       siocatmarkpair(true);
+
+       recvpair("x", 1, 1, MSG_OOB);
+       epollpair(false);
+       siocatmarkpair(true);
+
+       sendpair("y", 1, MSG_OOB);
+       epollpair(true);
+       siocatmarkpair(true);
+
+       recvpair("", -EAGAIN, 1, 0);
+       epollpair(false);
+       siocatmarkpair(false);
+
+       recvpair("", -EINVAL, 1, MSG_OOB);
+       epollpair(false);
+       siocatmarkpair(false);
+}
+
+
 TEST_F(msg_oob, ex_oob_ahead_break)
 {
      sendpair("hello", 5, MSG_OOB);

[root@turbo-2 af_unix]# rm msg_oob
rm: remove regular file 'msg_oob'? y
[root@turbo-2 af_unix]# make msg_oob
gcc -isystem 
/home/rshoaib/debug_pnic/linux/tools/testing/selftests/../../../usr/include 
-D_GNU_SOURCE=     msg_oob.c   -o msg_oob

root@turbo-2 af_unix]# echo 1 > /proc/sys/kernel/panic_on_warn

./msg_oob
TAP version 13
1..40
# Starting 40 tests from 2 test cases.
#  RUN           msg_oob.no_peek.non_oob ...
#            OK  msg_oob.no_peek.non_oob
ok 1 msg_oob.no_peek.non_oob
#  RUN           msg_oob.no_peek.oob ...
#            OK  msg_oob.no_peek.oob
ok 2 msg_oob.no_peek.oob
#  RUN           msg_oob.no_peek.oob_drop ...
#            OK  msg_oob.no_peek.oob_drop
ok 3 msg_oob.no_peek.oob_drop
#  RUN           msg_oob.no_peek.oob_ahead ...
#            OK  msg_oob.no_peek.oob_ahead
ok 4 msg_oob.no_peek.oob_ahead
#  RUN           msg_oob.no_peek.oob_break ...
#            OK  msg_oob.no_peek.oob_break
ok 5 msg_oob.no_peek.oob_break
#  RUN           msg_oob.no_peek.oob_ahead_break ...
#            OK  msg_oob.no_peek.oob_ahead_break
ok 6 msg_oob.no_peek.oob_ahead_break
#  RUN           msg_oob.no_peek.oob_break_drop ...
#            OK  msg_oob.no_peek.oob_break_drop
ok 7 msg_oob.no_peek.oob_break_drop
#  RUN           msg_oob.no_peek.ex_oob_break ...
#            OK  msg_oob.no_peek.ex_oob_break
ok 8 msg_oob.no_peek.ex_oob_break
#  RUN           msg_oob.no_peek.ex_oob_drop ...
# msg_oob.c:242:ex_oob_drop:AF_UNIX :x
# msg_oob.c:243:ex_oob_drop:TCP     :Resource temporarily unavailable
# msg_oob.c:242:ex_oob_drop:AF_UNIX :y
# msg_oob.c:243:ex_oob_drop:TCP     :Invalid argument
#            OK  msg_oob.no_peek.ex_oob_drop
ok 9 msg_oob.no_peek.ex_oob_drop
#  RUN           msg_oob.no_peek.ex_oob_drop_2 ...
# msg_oob.c:242:ex_oob_drop_2:AF_UNIX :x
# msg_oob.c:243:ex_oob_drop_2:TCP     :Resource temporarily unavailable
#            OK  msg_oob.no_peek.ex_oob_drop_2
ok 10 msg_oob.no_peek.ex_oob_drop_2
#  RUN           msg_oob.no_peek.ex_oob_oob ...
# msg_oob.c:305:ex_oob_oob:Expected answ[0] (0) == oob_head (1)
# ex_oob_oob: Test terminated by assertion
#          FAIL  msg_oob.no_peek.ex_oob_oob
<...>
ok 38 msg_oob.peek.inline_ex_oob_no_drop
#  RUN           msg_oob.peek.inline_ex_oob_drop ...
# msg_oob.c:267:inline_ex_oob_drop:AF_UNIX :x
# msg_oob.c:268:inline_ex_oob_drop:TCP     :y
# msg_oob.c:267:inline_ex_oob_drop:AF_UNIX :x
# msg_oob.c:268:inline_ex_oob_drop:TCP     :y
# msg_oob.c:242:inline_ex_oob_drop:AF_UNIX :y
# msg_oob.c:243:inline_ex_oob_drop:TCP     :Resource temporarily unavailable
# msg_oob.c:242:inline_ex_oob_drop:AF_UNIX :y
# msg_oob.c:243:inline_ex_oob_drop:TCP     :Resource temporarily unavailable
#            OK  msg_oob.peek.inline_ex_oob_drop
ok 39 msg_oob.peek.inline_ex_oob_drop
#  RUN           msg_oob.peek.inline_ex_oob_siocatmark ...
#            OK  msg_oob.peek.inline_ex_oob_siocatmark
ok 40 msg_oob.peek.inline_ex_oob_siocatmark
# FAILED: 38 / 40 tests passed.
# Totals: pass:38 fail:2 xfail:0 xpass:0 skip:0 error:0

[root@turbo-2 af_unix]# uname -r
6.11.0-rao-rc6-gc763c4339688-dirty

[root@turbo-2 af_unix]# journalctl -r | grep -i kasan
Sep  6 21:15:25 turbo-2 kernel: kasan: KernelAddressSanitizer initialized