Messages in this thread | | | From | Arnd Bergmann <> | Date | Tue, 11 Jun 2019 14:39:01 +0200 | Subject | Re: KASAN: null-ptr-deref Read in x25_connect |
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On Tue, Jun 11, 2019 at 9:18 AM syzbot <syzbot+777a2aab6ffd397407b5@syzkaller.appspotmail.com> wrote: > > Hello, > > syzbot found the following crash on: > > HEAD commit: f4cfcfbd net: dsa: sja1105: Fix link speed not working at .. > git tree: net > console output: https://syzkaller.appspot.com/x/log.txt?x=16815cd2a00000 > kernel config: https://syzkaller.appspot.com/x/.config?x=4f721a391cd46ea > dashboard link: https://syzkaller.appspot.com/bug?extid=777a2aab6ffd397407b5 > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > Unfortunately, I don't have any reproducer for this crash yet. > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+777a2aab6ffd397407b5@syzkaller.appspotmail.com
Not sure why I was on Cc on this (I know nothing about x25), but I had a brief look and found that this is in the error path of x25_connect, after "goto out_put_neigh", with x25->neighbour==NULL.
This would indicate that either 'x25' is being freed between the "if (!x25->neighbour)" check in that function and the x25_neigh_put(x25->neighbour), or that there are two concurrent calls to x25_connect, with both failing, so one sets x25->neighbour=NULL before the other one checks it.
Arnd
> ================================================================== > BUG: KASAN: null-ptr-deref in atomic_read > include/asm-generic/atomic-instrumented.h:26 [inline] > BUG: KASAN: null-ptr-deref in refcount_sub_and_test_checked+0x87/0x200 > lib/refcount.c:182 > Read of size 4 at addr 00000000000000c8 by task syz-executor.2/16959 > > CPU: 0 PID: 16959 Comm: syz-executor.2 Not tainted 5.2.0-rc2+ #40 > 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+0x172/0x1f0 lib/dump_stack.c:113 > __kasan_report.cold+0x5/0x40 mm/kasan/report.c:321 > kasan_report+0x12/0x20 mm/kasan/common.c:614 > check_memory_region_inline mm/kasan/generic.c:185 [inline] > check_memory_region+0x123/0x190 mm/kasan/generic.c:191 > kasan_check_read+0x11/0x20 mm/kasan/common.c:94 > atomic_read include/asm-generic/atomic-instrumented.h:26 [inline] > refcount_sub_and_test_checked+0x87/0x200 lib/refcount.c:182 > refcount_dec_and_test_checked+0x1b/0x20 lib/refcount.c:220 > x25_neigh_put include/net/x25.h:252 [inline] > x25_connect+0x8d8/0xea0 net/x25/af_x25.c:820 > __sys_connect+0x264/0x330 net/socket.c:1840 > __do_sys_connect net/socket.c:1851 [inline] > __se_sys_connect net/socket.c:1848 [inline] > __x64_sys_connect+0x73/0xb0 net/socket.c:1848 > do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > RIP: 0033:0x459279 > Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 > 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff > ff 0f 83 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 > RSP: 002b:00007f09776b4c78 EFLAGS: 00000246 ORIG_RAX: 000000000000002a > RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459279 > RDX: 0000000000000012 RSI: 0000000020000280 RDI: 0000000000000004 > RBP: 000000000075bfc0 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 00007f09776b56d4 > R13: 00000000004bf854 R14: 00000000004d0e08 R15: 00000000ffffffff > ================================================================== > > > --- > This bug is generated by a bot. It may contain errors. > See https://goo.gl/tpsmEJ for more information about syzbot. > syzbot engineers can be reached at syzkaller@googlegroups.com. > > syzbot will keep track of this bug report. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
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