Messages in this thread | | | From | Dmitry Vyukov <> | Date | Thu, 30 Nov 2017 12:31:18 +0100 | Subject | Re: general protection fault in show_timer |
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On Thu, Nov 30, 2017 at 12:08 PM, Alexey Dobriyan <adobriyan@gmail.com> wrote: > On 11/30/17, syzbot > <bot+054c6cd125793643a90db21e4b9ddc71a881f797@syzkaller.appspotmail.com> > wrote: >> Hello, >> >> syzkaller hit the following crash on >> 43570f0383d6d5879ae585e6c3cf027ba321546f >> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master >> compiler: gcc (GCC) 7.1.1 20170620 >> .config is attached >> Raw console output is attached. >> >> Unfortunately, I don't have any reproducer for this bug yet. >> >> >> kasan: CONFIG_KASAN_INLINE enabled >> kasan: GPF could be caused by NULL-ptr deref or user memory access >> general protection fault: 0000 [#1] SMP KASAN >> Dumping ftrace buffer: >> (ftrace buffer empty) >> Modules linked in: >> CPU: 1 PID: 22618 Comm: syz-executor4 Not tainted 4.15.0-rc1+ #199 >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS >> Google 01/01/2011 >> task: ffff8801c048c400 task.stack: ffff8801cd968000 >> RIP: 0010:show_timer+0x1c7/0x2b0 fs/proc/base.c:2274 >> RSP: 0018:ffff8801cd96f9e0 EFLAGS: 00010006 >> RAX: dffffc0000000000 RBX: ffff8801cff22e40 RCX: ffffffff81ccb88e >> RDX: 0000000030a68524 RSI: ffffc90002dea000 RDI: 0000000185342920 >> RBP: ffff8801cd96fa10 R08: ffffed003a0514c5 R09: ffffed003a0514c5 >> R10: ffff8801c048c400 R11: ffffed003a0514c4 R12: 0000000040000000 >> R13: ffff8801c79e7000 R14: ffffffff853419e0 R15: 0000000000000507 >> FS: 00007f19f811e700(0000) GS:ffff8801db500000(0000) >> knlGS:0000000000000000 >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> CR2: 00007f4ab586bdb8 CR3: 00000001d1788000 CR4: 00000000001426e0 >> DR0: 0000000020000000 DR1: 0000000020000008 DR2: 0000000000000000 >> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600 >> Call Trace: >> traverse+0x248/0xa00 fs/seq_file.c:111 >> seq_read+0x96a/0x13d0 fs/seq_file.c:189 >> do_loop_readv_writev fs/read_write.c:673 [inline] >> do_iter_read+0x3db/0x5b0 fs/read_write.c:897 >> vfs_readv+0x121/0x1c0 fs/read_write.c:959 >> do_preadv+0x11b/0x1a0 fs/read_write.c:1043 >> SYSC_preadv fs/read_write.c:1093 [inline] >> SyS_preadv+0x30/0x40 fs/read_write.c:1088 >> entry_SYSCALL_64_fastpath+0x1f/0x96 >> RIP: 0033:0x4529d9 >> RSP: 002b:00007f19f811dc58 EFLAGS: 00000212 ORIG_RAX: 0000000000000127 >> RAX: ffffffffffffffda RBX: 00007f19f811d950 RCX: 00000000004529d9 >> RDX: 0000000000000001 RSI: 00000000205e2ff0 RDI: 0000000000000013 >> RBP: 00007f19f811d940 R08: 0000000000000000 R09: 0000000000000000 >> R10: 0001000000000000 R11: 0000000000000212 R12: 00000000004b7346 >> R13: 00007f19f811dac8 R14: 00000000004b7351 R15: 0000000000000000 >> Code: 89 c7 4c 0f 44 f1 41 83 e4 fb 4d 63 e4 e8 a2 2f a3 ff 4a 8d 3c e5 20 >> >> 29 34 85 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 >> 0f 85 a2 00 00 00 4a 8b 14 e5 20 29 34 85 4c 89 ef >> RIP: show_timer+0x1c7/0x2b0 fs/proc/base.c:2274 RSP: ffff8801cd96f9e0 > > This looks like ASAN problem > > ffffffff81a5f1d9: e8 72 74 b7 ff call > ffffffff815d6650 <__sanitizer_cov_trace_pc> > ffffffff81a5f1de: 4a 8d 3c e5 a0 9e b4 lea rdi,[r12*8-0x7b4b6160] > ffffffff81a5f1e5: 84 > ffffffff81a5f1e6: 48 b8 00 00 00 00 00 movabs rax,0xdffffc0000000000 > ffffffff81a5f1ed: fc ff df > ffffffff81a5f1f0: 48 89 fa mov rdx,rdi > ffffffff81a5f1f3: 48 c1 ea 03 shr rdx,0x3 > ffffffff81a5f1f7: 80 3c 02 00 ===>cmp BYTE PTR > [rdx+rax*1],0x0 <==== > > This is code injected by KASAN_INLINE > > timer_show() looks seemingly fine: > "timer" pointer is valid otherwise code would oopsed earlier > tp->ns is valid otherwise it'd oopsed inside pid_nr_ns()
This is not KASAN bug. Kernel tries to dereference 0x0000000185342920. Failure mode is just different.
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