[syzbot] KMSAN: uninit-value in do_mbind

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    4ebaab5f kmsan: drop unneeded references to kmsan_context_..
git tree:       https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=11b6bfe5d00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=647ca0f5bbe7703a
dashboard link: https://syzkaller.appspot.com/bug?extid=0bdecd1b2c19a1faa92d
compiler:       Debian clang version 11.0.1-2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11012825d00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1425f45dd00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0bdecd1b2c19a1faa92d@xxxxxxxxxxxxxxxxxxxxxxxxx

=====================================================
BUG: KMSAN: uninit-value in __mpol_equal mm/mempolicy.c:2340 [inline]
BUG: KMSAN: uninit-value in mpol_equal include/linux/mempolicy.h:108 [inline]
BUG: KMSAN: uninit-value in mbind_range mm/mempolicy.c:825 [inline]
BUG: KMSAN: uninit-value in do_mbind+0x2d1b/0x38c0 mm/mempolicy.c:1350
CPU: 0 PID: 8220 Comm: syz-executor545 Not tainted 5.12.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x24c/0x2e0 lib/dump_stack.c:120
 kmsan_report+0xfb/0x1e0 mm/kmsan/kmsan_report.c:118
 __msan_warning+0x5c/0xa0 mm/kmsan/kmsan_instr.c:197
 __mpol_equal mm/mempolicy.c:2340 [inline]
 mpol_equal include/linux/mempolicy.h:108 [inline]
 mbind_range mm/mempolicy.c:825 [inline]
 do_mbind+0x2d1b/0x38c0 mm/mempolicy.c:1350
 kernel_mbind mm/mempolicy.c:1478 [inline]
 __do_sys_mbind mm/mempolicy.c:1485 [inline]
 __se_sys_mbind+0x3a6/0x3c0 mm/mempolicy.c:1481
 __x64_sys_mbind+0x6e/0x90 mm/mempolicy.c:1481
 do_syscall_64+0x9f/0x140 arch/x86/entry/common.c:48
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x4456f9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 15 00 00 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f4c4152c308 EFLAGS: 00000246 ORIG_RAX: 00000000000000ed
RAX: ffffffffffffffda RBX: 00000000004ca408 RCX: 00000000004456f9
RDX: 0000000000002001 RSI: 0000000000800000 RDI: 0000000020001000
RBP: 00000000004ca400 R08: 0000000000000007 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004ca40c
R13: 00007ffe6c9a98ff R14: 00007f4c4152c400 R15: 0000000000022000

Uninit was created at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:121 [inline]
 kmsan_internal_poison_shadow+0x5c/0xf0 mm/kmsan/kmsan.c:104
 kmsan_slab_alloc+0x8e/0xe0 mm/kmsan/kmsan_hooks.c:76
 slab_alloc_node mm/slub.c:2922 [inline]
 slab_alloc mm/slub.c:2931 [inline]
 kmem_cache_alloc+0x895/0x1030 mm/slub.c:2936
 mpol_new mm/mempolicy.c:302 [inline]
 do_mbind+0x8d5/0x38c0 mm/mempolicy.c:1306
 kernel_mbind mm/mempolicy.c:1478 [inline]
 __do_sys_mbind mm/mempolicy.c:1485 [inline]
 __se_sys_mbind+0x3a6/0x3c0 mm/mempolicy.c:1481
 __x64_sys_mbind+0x6e/0x90 mm/mempolicy.c:1481
 do_syscall_64+0x9f/0x140 arch/x86/entry/common.c:48
 entry_SYSCALL_64_after_hwframe+0x44/0xae
=====================================================


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