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Message-ID: <202208110830.8F528D6737@keescook>
Date: Thu, 11 Aug 2022 08:33:16 -0700
From: Kees Cook <keescook@...omium.org>
To: "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc: ebiederm@...ssion.com, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
linux-next@...r.kernel.org, sfr@...b.auug.org.au,
syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk,
syzbot <syzbot+3250d9c8925ef29e975f@...kaller.appspotmail.com>,
Ira Weiny <ira.weiny@...el.com>
Subject: Re: [syzbot] linux-next boot error: BUG: unable to handle kernel
paging request in kernel_execve
Hi Fabio,
It seems likely that the kmap change[1] might be causing this crash. Is
there a boot-time setup race between kmap being available and early umh
usage?
-Kees
[1] https://git.kernel.org/linus/c6e8e36c6ae4b11bed5643317afb66b6c3cadba8
On Thu, Aug 11, 2022 at 12:29:34AM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: bc6c6584ffb2 Add linux-next specific files for 20220810
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=115034c3080000
> kernel config: https://syzkaller.appspot.com/x/.config?x=5784be4315a4403b
> dashboard link: https://syzkaller.appspot.com/bug?extid=3250d9c8925ef29e975f
> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+3250d9c8925ef29e975f@...kaller.appspotmail.com
>
> BUG: unable to handle page fault for address: ffffdc0000000000
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> PGD 11826067 P4D 11826067 PUD 0
> Oops: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 1100 Comm: kworker/u4:5 Not tainted 5.19.0-next-20220810-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
> RIP: 0010:strnlen+0x3b/0x70 lib/string.c:504
> Code: 74 3c 48 bb 00 00 00 00 00 fc ff df 49 89 fc 48 89 f8 eb 09 48 83 c0 01 48 39 e8 74 1e 48 89 c2 48 89 c1 48 c1 ea 03 83 e1 07 <0f> b6 14 1a 38 ca 7f 04 84 d2 75 11 80 38 00 75 d9 4c 29 e0 48 83
> RSP: 0000:ffffc90005c5fe10 EFLAGS: 00010246
> RAX: ffff000000000000 RBX: dffffc0000000000 RCX: 0000000000000000
> RDX: 1fffe00000000000 RSI: 0000000000020000 RDI: ffff000000000000
> RBP: ffff000000020000 R08: 0000000000000005 R09: 0000000000000000
> R10: 0000000000000006 R11: 0000000000000000 R12: ffff000000000000
> R13: ffff88814764cc00 R14: ffff000000000000 R15: ffff88814764cc00
> FS: 0000000000000000(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffdc0000000000 CR3: 000000000bc8e000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <TASK>
> strnlen include/linux/fortify-string.h:119 [inline]
> copy_string_kernel+0x26/0x250 fs/exec.c:616
> copy_strings_kernel+0xb3/0x190 fs/exec.c:655
> kernel_execve+0x377/0x500 fs/exec.c:1998
> call_usermodehelper_exec_async+0x2e3/0x580 kernel/umh.c:112
> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
> </TASK>
> Modules linked in:
> CR2: ffffdc0000000000
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:strnlen+0x3b/0x70 lib/string.c:504
> Code: 74 3c 48 bb 00 00 00 00 00 fc ff df 49 89 fc 48 89 f8 eb 09 48 83 c0 01 48 39 e8 74 1e 48 89 c2 48 89 c1 48 c1 ea 03 83 e1 07 <0f> b6 14 1a 38 ca 7f 04 84 d2 75 11 80 38 00 75 d9 4c 29 e0 48 83
> RSP: 0000:ffffc90005c5fe10 EFLAGS: 00010246
> RAX: ffff000000000000 RBX: dffffc0000000000 RCX: 0000000000000000
> RDX: 1fffe00000000000 RSI: 0000000000020000 RDI: ffff000000000000
> RBP: ffff000000020000 R08: 0000000000000005 R09: 0000000000000000
> R10: 0000000000000006 R11: 0000000000000000 R12: ffff000000000000
> R13: ffff88814764cc00 R14: ffff000000000000 R15: ffff88814764cc00
> FS: 0000000000000000(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffdc0000000000 CR3: 000000000bc8e000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ----------------
> Code disassembly (best guess):
> 0: 74 3c je 0x3e
> 2: 48 bb 00 00 00 00 00 movabs $0xdffffc0000000000,%rbx
> 9: fc ff df
> c: 49 89 fc mov %rdi,%r12
> f: 48 89 f8 mov %rdi,%rax
> 12: eb 09 jmp 0x1d
> 14: 48 83 c0 01 add $0x1,%rax
> 18: 48 39 e8 cmp %rbp,%rax
> 1b: 74 1e je 0x3b
> 1d: 48 89 c2 mov %rax,%rdx
> 20: 48 89 c1 mov %rax,%rcx
> 23: 48 c1 ea 03 shr $0x3,%rdx
> 27: 83 e1 07 and $0x7,%ecx
> * 2a: 0f b6 14 1a movzbl (%rdx,%rbx,1),%edx <-- trapping instruction
> 2e: 38 ca cmp %cl,%dl
> 30: 7f 04 jg 0x36
> 32: 84 d2 test %dl,%dl
> 34: 75 11 jne 0x47
> 36: 80 38 00 cmpb $0x0,(%rax)
> 39: 75 d9 jne 0x14
> 3b: 4c 29 e0 sub %r12,%rax
> 3e: 48 rex.W
> 3f: 83 .byte 0x83
>
>
> ---
> 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@...glegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
--
Kees Cook
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