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SubjectRe: KMSAN: uninit-value in sctp_ootb_pkt_new
From
syzbot has found a reproducer for the following crash on:

HEAD commit: bfa90a4a kmsan: remove __GFP_NO_KMSAN_SHADOW
git tree: https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=13ab7fbfe00000
kernel config: https://syzkaller.appspot.com/x/.config?x=a5915107b3106aaa
dashboard link: https://syzkaller.appspot.com/bug?extid=6751381fe5a26df5b74d
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=138df47fe00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=158a182fe00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+6751381fe5a26df5b74d@syzkaller.appspotmail.com

batman_adv: batadv0: Interface activated: batadv_slave_1
=====================================================
BUG: KMSAN: uninit-value in __arch_swab32 arch/x86/include/uapi/asm/swab.h:10 [inline]
BUG: KMSAN: uninit-value in __fswab32 include/uapi/linux/swab.h:60 [inline]
BUG: KMSAN: uninit-value in sctp_ootb_pkt_new+0x202/0x540 net/sctp/sm_statefuns.c:6256
CPU: 0 PID: 8800 Comm: syz-executor949 Not tainted 5.6.0-rc7-syzkaller #0
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+0x1c9/0x220 lib/dump_stack.c:118
kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:118
__msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215
__arch_swab32 arch/x86/include/uapi/asm/swab.h:10 [inline]
__fswab32 include/uapi/linux/swab.h:60 [inline]
sctp_ootb_pkt_new+0x202/0x540 net/sctp/sm_statefuns.c:6256
sctp_sf_tabort_8_4_8+0xe6/0x7e0 net/sctp/sm_statefuns.c:3372
sctp_sf_do_5_1B_init+0x6be/0x1b60 net/sctp/sm_statefuns.c:338
sctp_do_sm+0x2b4/0x9a30 net/sctp/sm_sideeffect.c:1153
sctp_endpoint_bh_rcv+0xd54/0xfe0 net/sctp/endpointola.c:395
sctp_inq_push+0x300/0x420 net/sctp/inqueue.c:80
sctp_rcv+0x48b9/0x5410 net/sctp/input.c:256
ip_protocol_deliver_rcu+0x700/0xbc0 net/ipv4/ip_input.c:204
ip_local_deliver_finish net/ipv4/ip_input.c:231 [inline]
NF_HOOK include/linux/netfilter.h:307 [inline]
ip_local_deliver+0x62a/0x7c0 net/ipv4/ip_input.c:252
dst_input include/net/dst.h:442 [inline]
ip_rcv_finish net/ipv4/ip_input.c:428 [inline]
NF_HOOK include/linux/netfilter.h:307 [inline]
ip_rcv+0x6cf/0x750 net/ipv4/ip_input.c:538
__netif_receive_skb_one_core net/core/dev.c:5187 [inline]
__netif_receive_skb net/core/dev.c:5301 [inline]
netif_receive_skb_internal net/core/dev.c:5391 [inline]
netif_receive_skb+0xbb5/0xf20 net/core/dev.c:5450
tun_rx_batched include/linux/skbuff.h:4351 [inline]
tun_get_user+0x6aef/0x6f60 drivers/net/tun.c:1997
tun_chr_write_iter+0x1f2/0x360 drivers/net/tun.c:2026
call_write_iter include/linux/fs.h:1902 [inline]
new_sync_write fs/read_write.c:483 [inline]
__vfs_write+0xa5a/0xca0 fs/read_write.c:496
vfs_write+0x44a/0x8f0 fs/read_write.c:558
ksys_write+0x267/0x450 fs/read_write.c:611
__do_sys_write fs/read_write.c:623 [inline]
__se_sys_write+0x92/0xb0 fs/read_write.c:620
__x64_sys_write+0x4a/0x70 fs/read_write.c:620
do_syscall_64+0xb8/0x160 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x443659
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 7b 10 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fff60095968 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000003172 RCX: 0000000000443659
RDX: 000000000000002e RSI: 00000000200000c0 RDI: 0000000000000003
RBP: 00007fff60095990 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000aa14 R11: 0000000000000246 R12: 656c6c616b7a7973
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Uninit was created at:
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:144 [inline]
kmsan_internal_poison_shadow+0x66/0xd0 mm/kmsan/kmsan.c:127
kmsan_slab_alloc+0x8a/0xe0 mm/kmsan/kmsan_hooks.c:80
slab_alloc_node mm/slub.c:2801 [inline]
__kmalloc_node_track_caller+0xb40/0x1200 mm/slub.c:4420
__kmalloc_reserve net/core/skbuff.c:142 [inline]
__alloc_skb+0x2fd/0xac0 net/core/skbuff.c:210
alloc_skb include/linux/skbuff.h:1081 [inline]
alloc_skb_with_frags+0x18c/0xa70 net/core/skbuff.c:5764
sock_alloc_send_pskb+0xada/0xc60 net/core/sock.c:2245
tun_alloc_skb drivers/net/tun.c:1529 [inline]
tun_get_user+0x10ae/0x6f60 drivers/net/tun.c:1843
tun_chr_write_iter+0x1f2/0x360 drivers/net/tun.c:2026
call_write_iter include/linux/fs.h:1902 [inline]
new_sync_write fs/read_write.c:483 [inline]
__vfs_write+0xa5a/0xca0 fs/read_write.c:496
vfs_write+0x44a/0x8f0 fs/read_write.c:558
ksys_write+0x267/0x450 fs/read_write.c:611
__do_sys_write fs/read_write.c:623 [inline]
__se_sys_write+0x92/0xb0 fs/read_write.c:620
__x64_sys_write+0x4a/0x70 fs/read_write.c:620
do_syscall_64+0xb8/0x160 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x44/0xa9
=====================================================

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