general protection fault in load_elf_binary

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    1baf02ec Add linux-next specific files for 20190329
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=107d8e53200000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9d8e70f94f3533a7
dashboard link: https://syzkaller.appspot.com/bug?extid=0d1fcd7268b21baced4a
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=125ca12f200000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11e1123f200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+0d1fcd7268b21baced4a@xxxxxxxxxxxxxxxxxxxxxxxxx

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
CPU: 0 PID: 7588 Comm: syz-executor559 Not tainted 5.1.0-rc2-next-20190329  
#14
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:allow_write_access include/linux/fs.h:2871 [inline]
RIP: 0010:load_elf_binary+0x167c/0x5b10 fs/binfmt_elf.c:1179
Code: b8 fe ff ff e8 65 8c db ff e8 70 23 a3 ff 48 8b 85 f8 fe ff ff 48 8d  
78 20 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f  
85 b2 3e 00 00 4c 8b bd f8 fe ff ff be 04 00 00 00
RSP: 0018:ffff88808db17bf8 EFLAGS: 00010207
RAX: dffffc0000000000 RBX: 00000000fffffffe RCX: 1ffffffff12be8fb
RDX: 0000000000000003 RSI: ffffffff81cd3e10 RDI: 000000000000001e
RBP: ffff88808db17d78 R08: ffff88808fc746c0 R09: fffffbfff11a6d55
R10: fffffbfff11a6d54 R11: ffffffff88d36aa3 R12: 0000000000000000
R13: ffff8880905992c0 R14: ffff8880962d7240 R15: ffff88809433aac0
FS:  00007f00b549e700(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020001140 CR3: 00000000902b1000 CR4: 00000000001406f0
Call Trace:
 search_binary_handler fs/exec.c:1656 [inline]
 search_binary_handler+0x17f/0x570 fs/exec.c:1634
 exec_binprm fs/exec.c:1698 [inline]
 __do_execve_file.isra.0+0x1394/0x23f0 fs/exec.c:1818
 do_execveat_common fs/exec.c:1865 [inline]
 do_execve fs/exec.c:1882 [inline]
 __do_sys_execve fs/exec.c:1958 [inline]
 __se_sys_execve fs/exec.c:1953 [inline]
 __x64_sys_execve+0x8f/0xc0 fs/exec.c:1953
 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x447139
Code: e8 4c 15 03 00 48 83 c4 18 c3 0f 1f 80 00 00 00 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 eb 0e fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f00b549dce8 EFLAGS: 00000246 ORIG_RAX: 000000000000003b
RAX: ffffffffffffffda RBX: 00000000006dcc28 RCX: 0000000000447139
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000180
RBP: 00000000006dcc20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dcc2c
R13: 00007ffcb2d5610f R14: 00007f00b549e9c0 R15: 0000000000000000
Modules linked in:
---[ end trace 2e60703d22657961 ]---
RIP: 0010:allow_write_access include/linux/fs.h:2871 [inline]
RIP: 0010:load_elf_binary+0x167c/0x5b10 fs/binfmt_elf.c:1179
Code: b8 fe ff ff e8 65 8c db ff e8 70 23 a3 ff 48 8b 85 f8 fe ff ff 48 8d  
78 20 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f  
85 b2 3e 00 00 4c 8b bd f8 fe ff ff be 04 00 00 00
RSP: 0018:ffff88808db17bf8 EFLAGS: 00010207
RAX: dffffc0000000000 RBX: 00000000fffffffe RCX: 1ffffffff12be8fb
RDX: 0000000000000003 RSI: ffffffff81cd3e10 RDI: 000000000000001e
RBP: ffff88808db17d78 R08: ffff88808fc746c0 R09: fffffbfff11a6d55
R10: fffffbfff11a6d54 R11: ffffffff88d36aa3 R12: 0000000000000000
R13: ffff8880905992c0 R14: ffff8880962d7240 R15: ffff88809433aac0
FS:  00007f00b549e700(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020001140 CR3: 00000000902b1000 CR4: 00000000001406f0


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