KMSAN: uninit-value in af_alg_free_areq_sgls

[syzbot]

Hello,

syzbot hit the following crash on  
https://github.com/google/kmsan.git/master commit
e2ab7e8abba47a2f2698216258e5d8727ae58717 (Fri Apr 6 16:24:31 2018 +0000)
kmsan: temporarily disable visitAsmInstruction() to help syzbot
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=9c251bdd09f83b92ba95

So far this crash happened 11 times on  
https://github.com/google/kmsan.git/master.
C reproducer: https://syzkaller.appspot.com/x/repro.c?id=5551473324720128
syzkaller reproducer:  
https://syzkaller.appspot.com/x/repro.syz?id=4782073151750144
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=5003160619843584
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=6627248707860932248
compiler: clang version 7.0.0 (trunk 329391)

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Reported-by: syzbot+9c251bdd09f83b92ba95@xxxxxxxxxxxxxxxxxxxxxxxxx
It will help syzbot understand when the bug is fixed. See footer for  
details.
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==================================================================
BUG: KMSAN: uninit-value in atomic_sub arch/x86/include/asm/atomic.h:65  
[inline]
BUG: KMSAN: uninit-value in af_alg_free_areq_sgls+0x5ff/0xb20  
crypto/af_alg.c:669
CPU: 1 PID: 3568 Comm: syzkaller909997 Not tainted 4.16.0+ #82
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x185/0x1d0 lib/dump_stack.c:53
 kmsan_report+0x142/0x240 mm/kmsan/kmsan.c:1067
 __msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:676
 atomic_sub arch/x86/include/asm/atomic.h:65 [inline]
 af_alg_free_areq_sgls+0x5ff/0xb20 crypto/af_alg.c:669
 af_alg_free_resources+0x66/0xf0 crypto/af_alg.c:1033
 _aead_recvmsg crypto/algif_aead.c:321 [inline]
 aead_recvmsg+0x9a4/0x2960 crypto/algif_aead.c:334
 aead_recvmsg_nokey+0x129/0x160 crypto/algif_aead.c:452
 sock_recvmsg_nosec net/socket.c:803 [inline]
 sock_recvmsg+0x1d0/0x230 net/socket.c:810
 ___sys_recvmsg+0x3fb/0x810 net/socket.c:2205
 __sys_recvmsg net/socket.c:2250 [inline]
 SYSC_recvmsg+0x298/0x3c0 net/socket.c:2262
 SyS_recvmsg+0x54/0x80 net/socket.c:2257
 do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x3d/0xa2
RIP: 0033:0x43ff29
RSP: 002b:00007ffd9919c808 EFLAGS: 00000207 ORIG_RAX: 000000000000002f
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 000000000043ff29
RDX: 0000000000000000 RSI: 0000000020000040 RDI: 0000000000000004
RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 00000000004002c8 R11: 0000000000000207 R12: 0000000000401850
R13: 00000000004018e0 R14: 0000000000000000 R15: 0000000000000000

Uninit was created at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:278 [inline]
 kmsan_internal_poison_shadow+0xb8/0x1b0 mm/kmsan/kmsan.c:188
 kmsan_kmalloc+0x94/0x100 mm/kmsan/kmsan.c:314
 __kmalloc+0x23c/0x350 mm/slub.c:3791
 kmalloc include/linux/slab.h:517 [inline]
 sock_kmalloc+0x14e/0x270 net/core/sock.c:1986
 af_alg_get_rsgl+0x427/0xe10 crypto/af_alg.c:1149
 _aead_recvmsg crypto/algif_aead.c:163 [inline]
 aead_recvmsg+0x953/0x2960 crypto/algif_aead.c:334
 aead_recvmsg_nokey+0x129/0x160 crypto/algif_aead.c:452
 sock_recvmsg_nosec net/socket.c:803 [inline]
 sock_recvmsg+0x1d0/0x230 net/socket.c:810
 ___sys_recvmsg+0x3fb/0x810 net/socket.c:2205
 __sys_recvmsg net/socket.c:2250 [inline]
 SYSC_recvmsg+0x298/0x3c0 net/socket.c:2262
 SyS_recvmsg+0x54/0x80 net/socket.c:2257
 do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x3d/0xa2
==================================================================


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