Messages in this thread | | | From | Alexey Dobriyan <> | Date | Thu, 30 Nov 2017 14:20:26 +0200 | Subject | Re: general protection fault in show_timer |
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[cc security@] 100% oops with interrupts disabled by nobody or kernel memory read
On 11/30/17, Dmitry Vyukov <dvyukov@google.com> wrote: > On Thu, Nov 30, 2017 at 12:31 PM, Dmitry Vyukov <dvyukov@google.com> wrote: >> 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.
I'm new to KASAN.
> it seems that notify is equal to 0x0000000040000000 and this makes > nstr[notify & ~SIGEV_THREAD_ID] a totally wild access.
[nods] you named the bug already
"notify" directly comes from userspace struct sigevent::sigev_notify without adult supervision.
Reproducer is timer_create + read(/proc/self/timers)
BUG: unable to handle kernel paging request at 00000000b3695f68 IP: show_timer+0x73/0xa0 PGD 3d18f067 P4D 3d18f067 PUD 0 Oops: 0000 [#1] PREEMPT SMP CPU: 0 PID: 2819 Comm: a.out Not tainted 4.15.0-rc1-00179-ga0908a1b7d68 #2 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1.fc27 04/01/2014 task: 00000000ea51a5c5 task.stack: 00000000d68c2dbc RIP: 0010:show_timer+0x73/0xa0 RSP: 0018:ffffc900001bfdd0 EFLAGS: 00010006 RAX: ffffffff814cddbd RBX: 0000000040000000 RCX: ffffffff814cddbd RDX: 0000000000000000 RSI: ffffffff814d9419 RDI: ffff88003dab9500 RBP: ffff88003dab9500 R08: 0000000000000b03 R09: 0000000000000007 R10: ffffc9000040b908 R11: ffff88003d9ce020 R12: ffff88003c1c6570 R13: ffff88003d514d80 R14: ffff88003dab9500 R15: ffff88003c1c6570 FS: 00007f52624f0700(0000) GS:ffff88003fc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000181414880 CR3: 000000003c243000 CR4: 00000000000006b0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: seq_read+0xe6/0x3b0 __vfs_read+0x1e/0x120 ? ptrace_do_notify+0x6a/0x80 vfs_read+0x84/0x110 SyS_read+0x3d/0xa0 do_syscall_64+0x4b/0x180 entry_SYSCALL64_slow_path+0x25/0x25 RIP: 0033:0x7f5261e15fc0 RSP: 002b:00007ffd2f89f5c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f5261e15fc0 RDX: 0000000000001000 RSI: 00007ffd2f89f620 RDI: 0000000000000003 RBP: 0000000000000000 R08: 00007f52620cce40 R09: 00007f5261d47c60 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000400574 R13: 00007ffd2f8a0700 R14: 0000000000000000 R15: 0000000000000000 Code: 89 f1 ff f6 c3 04 48 89 ef 48 c7 c1 c9 44 4c 81 41 89 c0 48 c7 c0 bd dd 4c 81 48 c7 c6 19 94 4d 81 48 0f 44 c8 83 e3 fb 48 63 db <48> 8b 14 dd 80 48 41 81 e8 f0 3b fd ff 41 8b 54 24 30 48 89 ef RIP: show_timer+0x73/0xa0 RSP: ffffc900001bfdd0 CR2: 0000000181414880 ---[ end trace 99049f704e3a24ad ]--- note: a.out[2819] exited with preempt_count 1 #include <string.h> #include <signal.h> #include <time.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <unistd.h>
int main(void) { struct sigevent sev; timer_t id; char buf[4096]; int fd;
memset(&sev, 0, sizeof(struct sigevent)); sev.sigev_value.sival_int = SIGEV_SIGNAL; sev.sigev_value.sival_ptr = (void *)1UL; sev.sigev_signo = 1; sev.sigev_notify = 0x40000000;
memset(&id, 0, sizeof(timer_t));
timer_create(CLOCK_MONOTONIC, &sev, &id); fd = open("/proc/self/timers", O_RDONLY); read(fd, buf, sizeof(buf));
return 0; }
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