general protection fault in bpf_skb_change_tail

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 8c958cd7 ANDROID: sdcardfs: Change current->fs under lock
git tree: android-4.14
console output: https://syzkaller.appspot.com/x/log.txt?x=1267c976400000
kernel config: https://syzkaller.appspot.com/x/.config?x=9b3b342f97278cde
dashboard link: https://syzkaller.appspot.com/bug?extid=159aa7d1074ed94f5e5b
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10b2dc5e400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1548a25e400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+159aa7...@syzkaller.appspotmail.com

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
audit: type=1400 audit(1538655349.192:7): avc: denied { map } for
pid=1777 comm="syz-executor161" path="/root/syz-executor161304275"
dev="sda1" ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN NOPTI
Modules linked in:
CPU: 0 PID: 1777 Comm: syz-executor161 Not tainted 4.14.73+ #16
task: ffff8801d2f74680 task.stack: ffff8801d0ab0000
RIP: 0010:__bpf_skb_max_len net/core/filter.c:2283 [inline]
RIP: 0010:____bpf_skb_change_tail net/core/filter.c:2370 [inline]
RIP: 0010:bpf_skb_change_tail+0x58/0xb90 net/core/filter.c:2367
RSP: 0018:ffff8801d0ab7800 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffff8801d0976a80 RCX: 00000000fffffff9
RDX: 0000000000000043 RSI: 00000000000000fe RDI: 0000000000000218
RBP: 0000000000000000 R08: ffffffff9c412a40 R09: 0000000000000000
R10: 1ffff1003a156f2b R11: 0000000000000001 R12: 00000000000000fe
R13: 1ffff1003a156f13 R14: ffffed003a156f30 R15: ffffc90000476088
FS: 0000000001237880(0000) GS:ffff8801db800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000200 CR3: 00000001d6eb2002 CR4: 00000000001606b0
Call Trace:
___bpf_prog_run+0x248e/0x5c70 kernel/bpf/core.c:1012
Code: fa 48 c1 ea 03 80 3c 02 00 0f 85 eb 09 00 00 48 b8 00 00 00 00 00 fc
ff df 48 8b 6b 10 48 8d bd 18 02 00 00 48 89 fa 48 c1 ea 03 <0f> b6 04 02
84 c0 74 08 3c 03 0f 8e 29 09 00 00 48 8d bd 26 02
RIP: __bpf_skb_max_len net/core/filter.c:2283 [inline] RSP: ffff8801d0ab7800
RIP: ____bpf_skb_change_tail net/core/filter.c:2370 [inline] RSP:
ffff8801d0ab7800
RIP: bpf_skb_change_tail+0x58/0xb90 net/core/filter.c:2367 RSP:
ffff8801d0ab7800
---[ end trace 862787b751063ac9 ]---
Kernel panic - not syncing: Fatal exception
Kernel Offset: 0x18e00000 from 0xffffffff81000000 (relocation range:
0xffffffff80000000-0xffffffffbfffffff)
Rebooting in 86400 seconds..


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