Re: KMSAN: uninit-value in audit_log_vformat (2)

On Mon, Apr 20, 2020 at 6:29 PM Paul Moore <paul(a)paul-moore.com&gt; wrote: > On Mon, Apr 20, 2020 at 1:35 AM syzbot > <syzbot+49e69b4d71a420ceda3e(a)syzkaller.appspotmail.com&gt; 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(a)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.