Re: [syzbot] general protection fault in legacy_parse_param

[Casey Schaufler]

On 7/2/2021 10:51 PM, Dmitry Vyukov wrote:
> On Sat, Jul 3, 2021 at 7:41 AM syzbot
> <syzbot+d1e3b1d92d25abf97943@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit:    62fb9874 Linux 5.13
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=12ffa118300000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=19404adbea015a58
>> dashboard link: https://syzkaller.appspot.com/bug?extid=d1e3b1d92d25abf97943
>> compiler:       Debian clang version 11.0.1-2
>>
>> Unfortunately, I don't have any reproducer for this issue yet.
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+d1e3b1d92d25abf97943@xxxxxxxxxxxxxxxxxxxxxxxxx
> +Casey for what looks like a smackfs issue

This is from the new mount infrastructure introduced by
David Howells in November 2018. It makes sense that there
may be a problem in SELinux as well, as the code was introduced
by the same developer at the same time for the same purpose.


>
> The crash was triggered by this test case:
>
> 21:55:33 executing program 1:
> r0 = fsopen(&(0x7f0000000040)='ext3\x00', 0x1)
> fsconfig$FSCONFIG_SET_STRING(r0, 0x1, &(0x7f00000002c0)='smackfsroot',
> &(0x7f0000000300)='default_permissions', 0x0)
>
> And I think the issue is in smack_fs_context_parse_param():
> https://elixir.bootlin.com/linux/latest/source/security/smack/smack_lsm.c#L691
>
> But it seems that selinux_fs_context_parse_param() contains the same issue:
> https://elixir.bootlin.com/linux/latest/source/security/selinux/hooks.c#L2919
> +So selinux maintainers as well.
>
>
>
>> general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
>> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
>> CPU: 0 PID: 20300 Comm: syz-executor.1 Not tainted 5.13.0-syzkaller #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>> RIP: 0010:memchr+0x2f/0x70 lib/string.c:1054
>> Code: 41 54 53 48 89 d3 41 89 f7 45 31 f6 49 bc 00 00 00 00 00 fc ff df 0f 1f 44 00 00 48 85 db 74 3b 48 89 fd 48 89 f8 48 c1 e8 03 <42> 0f b6 04 20 84 c0 75 0f 48 ff cb 48 8d 7d 01 44 38 7d 00 75 db
>> RSP: 0018:ffffc90001dafd00 EFLAGS: 00010246
>> RAX: 0000000000000000 RBX: 0000000000000013 RCX: dffffc0000000000
>> RDX: 0000000000000013 RSI: 000000000000002c RDI: 0000000000000000
>> RBP: 0000000000000000 R08: ffffffff81e171bf R09: ffffffff81e16f95
>> R10: 0000000000000002 R11: ffff88807e96b880 R12: dffffc0000000000
>> R13: ffff888020894000 R14: 0000000000000000 R15: 000000000000002c
>> FS:  00007fe01ae27700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00000000005645a8 CR3: 0000000018afc000 CR4: 00000000001506f0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>>  legacy_parse_param+0x461/0x7e0 fs/fs_context.c:537
>>  vfs_parse_fs_param+0x1e5/0x460 fs/fs_context.c:117
>>  vfs_fsconfig_locked fs/fsopen.c:265 [inline]
>>  __do_sys_fsconfig fs/fsopen.c:439 [inline]
>>  __se_sys_fsconfig+0xba9/0xff0 fs/fsopen.c:314
>>  do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
>>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>> RIP: 0033:0x4665d9
>> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
>> RSP: 002b:00007fe01ae27188 EFLAGS: 00000246 ORIG_RAX: 00000000000001af
>> RAX: ffffffffffffffda RBX: 000000000056bf80 RCX: 00000000004665d9
>> RDX: 00000000200002c0 RSI: 0000000000000001 RDI: 0000000000000003
>> RBP: 00000000004bfcb9 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000020000300 R11: 0000000000000246 R12: 000000000056bf80
>> R13: 00007ffd4bb7c5bf R14: 00007fe01ae27300 R15: 0000000000022000
>> Modules linked in:
>> ---[ end trace 5d7119165725bd63 ]---
>> RIP: 0010:memchr+0x2f/0x70 lib/string.c:1054
>> Code: 41 54 53 48 89 d3 41 89 f7 45 31 f6 49 bc 00 00 00 00 00 fc ff df 0f 1f 44 00 00 48 85 db 74 3b 48 89 fd 48 89 f8 48 c1 e8 03 <42> 0f b6 04 20 84 c0 75 0f 48 ff cb 48 8d 7d 01 44 38 7d 00 75 db
>> RSP: 0018:ffffc90001dafd00 EFLAGS: 00010246
>> RAX: 0000000000000000 RBX: 0000000000000013 RCX: dffffc0000000000
>> RDX: 0000000000000013 RSI: 000000000000002c RDI: 0000000000000000
>> RBP: 0000000000000000 R08: ffffffff81e171bf R09: ffffffff81e16f95
>> R10: 0000000000000002 R11: ffff88807e96b880 R12: dffffc0000000000
>> R13: ffff888020894000 R14: 0000000000000000 R15: 000000000000002c
>> FS:  00007fe01ae27700(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00000000004e4da0 CR3: 0000000018afc000 CR4: 00000000001506e0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>
>>
>> ---
>> This report 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@xxxxxxxxxxxxxxxx.
>>
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>>
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