KMSAN: uninit-value in aa_fqlookupn_profile

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 7ace43031cfc kmsan, kcov: don't check atomic functions in ..
git tree: https://github.com/google/kmsan.git/master
console output: https://syzkaller.appspot.com/x/log.txt?x=17b97111400000
kernel config: https://syzkaller.appspot.com/x/.config?x=94a9ed72288f7fef
dashboard link: https://syzkaller.appspot.com/bug?extid=3a0d172d51be1b3de837
compiler: clang version 8.0.0 (trunk 339414)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=179819f1400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14761bae400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+3a0d17...@syzkaller.appspotmail.com

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
==================================================================
BUG: KMSAN: uninit-value in aa_fqlookupn_profile+0x33a/0x750
security/apparmor/policy.c:467
CPU: 0 PID: 4663 Comm: syz-executor299 Not tainted 4.19.0-rc4+ #56
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+0x2f6/0x430 lib/dump_stack.c:113
kmsan_report+0x183/0x2b0 mm/kmsan/kmsan.c:956
__msan_warning+0x70/0xc0 mm/kmsan/kmsan_instr.c:645
aa_fqlookupn_profile+0x33a/0x750 security/apparmor/policy.c:467
aa_label_strn_parse+0x179e/0x1f30 security/apparmor/label.c:1841
aa_label_parse+0x11f/0x130 security/apparmor/label.c:1943
aa_change_profile+0x979/0x41d0 security/apparmor/domain.c:1362
apparmor_setprocattr+0x121a/0x12f0 security/apparmor/lsm.c:651
security_setprocattr+0x139/0x210 security/security.c:1298
proc_pid_attr_write+0x3f9/0x4e0 fs/proc/base.c:2555
__vfs_write+0x1a8/0xa50 fs/read_write.c:485
vfs_write+0x495/0x8e0 fs/read_write.c:549
ksys_write fs/read_write.c:598 [inline]
__do_sys_write fs/read_write.c:610 [inline]
__se_sys_write+0x173/0x350 fs/read_write.c:607
__x64_sys_write+0x4a/0x70 fs/read_write.c:607
do_syscall_64+0xb8/0x100 arch/x86/entry/common.c:291
entry_SYSCALL_64_after_hwframe+0x63/0xe7
RIP: 0033:0x440059
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffd4b1e0f18 EFLAGS: 00000213 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440059
RDX: 0000000000000009 RSI: 0000000020000040 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000000 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000213 R12: 00000000004018e0
R13: 0000000000401970 R14: 0000000000000000 R15: 0000000000000000

Local variable description: ----ns_name@aa_fqlookupn_profile
Variable was created at:
aa_fqlookupn_profile+0x81/0x750 security/apparmor/policy.c:460
aa_label_strn_parse+0x179e/0x1f30 security/apparmor/label.c:1841
==================================================================


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[Eric Biggers]

#syz fix: apparmor: Fix uninitialized value in aa_split_fqname