Messages in this thread | | | From | Paul Moore <> | Date | Mon, 20 Apr 2020 16:26:21 -0400 | Subject | Re: KMSAN: uninit-value in audit_log_vformat (2) |
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On Mon, Apr 20, 2020 at 2:12 PM Dmitry Vyukov <dvyukov@google.com> wrote: > On Mon, Apr 20, 2020 at 6:29 PM Paul Moore <paul@paul-moore.com> wrote: > > On Mon, Apr 20, 2020 at 1:35 AM syzbot > > <syzbot+49e69b4d71a420ceda3e@syzkaller.appspotmail.com> wrote: > > > > > > Hello, > > > > > > syzbot found the following crash on: > > > > > > HEAD commit: 5356842d [EXPERIMENTAL] kmsan: eagerly allocate shadow at .. > > > git tree: https://github.com/google/kmsan.git master > > > console output: https://syzkaller.appspot.com/x/log.txt?x=12f06720100000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=a5915107b3106aaa > > > dashboard link: https://syzkaller.appspot.com/bug?extid=49e69b4d71a420ceda3e > > > compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81) > > > userspace arch: i386 > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=133b5dabe00000 > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=143e1610100000 > > > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > > Reported-by: syzbot+49e69b4d71a420ceda3e@syzkaller.appspotmail.com > > > > > > ===================================================== > > > BUG: KMSAN: uninit-value in string_nocheck lib/vsprintf.c:608 [inline] > > > BUG: KMSAN: uninit-value in string+0x522/0x690 lib/vsprintf.c:689 > > > CPU: 1 PID: 8854 Comm: syz-executor694 Not tainted 5.6.0-rc7-syzkaller #0 > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > > Call Trace: > > > __dump_stack lib/dump_stack.c:77 [inline] > > > dump_stack+0x1c9/0x220 lib/dump_stack.c:118 > > > kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:118 > > > __msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215 > > > string_nocheck lib/vsprintf.c:608 [inline] > > > string+0x522/0x690 lib/vsprintf.c:689 > > > vsnprintf+0x207d/0x31b0 lib/vsprintf.c:2574 > > > > Are there any ongoing problems with [vsn]printf() in the kernel at the > > moment with syzbot? > > > > I ask because on first look I'm not seeing any obvious problems in the > > audit portion of this code path. > > None I am aware of. Alex? > Can it be related to data_len==0? I don't see any obvious checks for > this. And in that case will 0-terminate out-of-bounds (at offset -1?) > and print potentially uninit data. But I looked at the code only very > briefly so potentially I am totally wrong.
Bingo, that's likely it. Thanks.
I was in the process of fixing another audit bug when I looked at this and got fixated on the varg stuff, not the variables themselves. I'll have a patch out later today.
-- paul moore www.paul-moore.com
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