[syzbot] general protection fault in mpol_parse_str

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    4d48f589d294 Add linux-next specific files for 20221021
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=165e12da880000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2c4b7d600a5739a6
dashboard link: https://syzkaller.appspot.com/bug?extid=a7f196a1dbf5e2c70568
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11f10ff6880000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=145f1ff2880000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0c86bd0b39a0/disk-4d48f589.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/074059d37f1f/vmlinux-4d48f589.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a7f196a1dbf5e2c70568@xxxxxxxxxxxxxxxxxxxxxxxxx

general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 1 PID: 3609 Comm: syz-executor110 Not tainted 6.1.0-rc1-next-20221021-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/11/2022
RIP: 0010:strchr+0x17/0xa0 lib/string.c:329
Code: 48 89 34 24 e8 5a 37 82 f8 48 8b 34 24 eb 9a 0f 1f 40 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 55 48 c1 ea 03 53 48 83 ec 10 <0f> b6 04 02 48 89 fa 83 e2 07 38 d0 7f 04 84 c0 75 51 0f b6 07 89
RSP: 0018:ffffc90003c3fad0 EFLAGS: 00010282
RAX: dffffc0000000000 RBX: 1ffff92000787f77 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 000000000000003a RDI: 0000000000000000
RBP: 1ffff92000787f62 R08: 0000000000000005 R09: 0000000000000009
R10: 0000000000000003 R11: 000000000008c001 R12: 0000000000000000
R13: 0000000000000000 R14: ffff88807e7e3b90 R15: dffffc0000000000
FS:  0000555557488300(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020001000 CR3: 00000000268e7000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 mpol_parse_str+0x79/0xa90 mm/mempolicy.c:2992
 shmem_parse_one+0x7d8/0xa60 mm/shmem.c:3508
 vfs_parse_fs_param fs/fs_context.c:148 [inline]
 vfs_parse_fs_param+0x1f9/0x3c0 fs/fs_context.c:129
 vfs_parse_fs_string+0xdb/0x170 fs/fs_context.c:191
 shmem_parse_options+0x15f/0x240 mm/shmem.c:3570
 do_new_mount fs/namespace.c:3036 [inline]
 path_mount+0x12de/0x1e20 fs/namespace.c:3370
 do_mount fs/namespace.c:3383 [inline]
 __do_sys_mount fs/namespace.c:3591 [inline]
 __se_sys_mount fs/namespace.c:3568 [inline]
 __x64_sys_mount+0x27f/0x300 fs/namespace.c:3568
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f34b3ddeb19
Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 00 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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffdebbcaee8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0030656c69662f2e RCX: 00007f34b3ddeb19
RDX: 0000000020000080 RSI: 0000000020000040 RDI: 0000000000000000
RBP: 00007f34b3da2cc0 R08: 0000000020000100 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f34b3da2d50
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:strchr+0x17/0xa0 lib/string.c:329
Code: 48 89 34 24 e8 5a 37 82 f8 48 8b 34 24 eb 9a 0f 1f 40 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 55 48 c1 ea 03 53 48 83 ec 10 <0f> b6 04 02 48 89 fa 83 e2 07 38 d0 7f 04 84 c0 75 51 0f b6 07 89
RSP: 0018:ffffc90003c3fad0 EFLAGS: 00010282
RAX: dffffc0000000000 RBX: 1ffff92000787f77 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 000000000000003a RDI: 0000000000000000
RBP: 1ffff92000787f62 R08: 0000000000000005 R09: 0000000000000009
R10: 0000000000000003 R11: 000000000008c001 R12: 0000000000000000
R13: 0000000000000000 R14: ffff88807e7e3b90 R15: dffffc0000000000
FS:  0000555557488300(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f34b3e51270 CR3: 00000000268e7000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	48 89 34 24          	mov    %rsi,(%rsp)
   4:	e8 5a 37 82 f8       	callq  0xf8823763
   9:	48 8b 34 24          	mov    (%rsp),%rsi
   d:	eb 9a                	jmp    0xffffffa9
   f:	0f 1f 40 00          	nopl   0x0(%rax)
  13:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  1a:	fc ff df
  1d:	48 89 fa             	mov    %rdi,%rdx
  20:	55                   	push   %rbp
  21:	48 c1 ea 03          	shr    $0x3,%rdx
  25:	53                   	push   %rbx
  26:	48 83 ec 10          	sub    $0x10,%rsp
* 2a:	0f b6 04 02          	movzbl (%rdx,%rax,1),%eax <-- trapping instruction
  2e:	48 89 fa             	mov    %rdi,%rdx
  31:	83 e2 07             	and    $0x7,%edx
  34:	38 d0                	cmp    %dl,%al
  36:	7f 04                	jg     0x3c
  38:	84 c0                	test   %al,%al
  3a:	75 51                	jne    0x8d
  3c:	0f b6 07             	movzbl (%rdi),%eax
  3f:	89                   	.byte 0x89


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