KASAN: invalid-free in put_files_struct

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    fcadab74 Merge tag 'drm-fixes-2020-10-01-1' of git://anong..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15d14513900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=89ab6a0c48f30b49
dashboard link: https://syzkaller.appspot.com/bug?extid=9cee17fa4a973a9e60f2
compiler:       gcc (GCC) 10.1.0-syz 20200507
userspace arch: i386

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9cee17fa4a973a9e60f2@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: double-free or invalid-free in put_files_struct fs/file.c:434 [inline]
BUG: KASAN: double-free or invalid-free in put_files_struct+0x2c8/0x350 fs/file.c:426

CPU: 0 PID: 27522 Comm: syz-executor.0 Not tainted 5.9.0-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+0x198/0x1fd lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xae/0x497 mm/kasan/report.c:383
 kasan_report_invalid_free+0x51/0x80 mm/kasan/report.c:477
 __kasan_slab_free+0x107/0x120 mm/kasan/common.c:401
 __cache_free mm/slab.c:3422 [inline]
 kmem_cache_free.part.0+0x74/0x1e0 mm/slab.c:3697
 put_files_struct fs/file.c:434 [inline]
 put_files_struct+0x2c8/0x350 fs/file.c:426
 exit_files+0x7e/0xa0 fs/file.c:458
 do_exit+0xb43/0x29f0 kernel/exit.c:801
 do_group_exit+0x125/0x310 kernel/exit.c:903
 get_signal+0x428/0x1f00 kernel/signal.c:2757
 arch_do_signal+0x82/0x2520 arch/x86/kernel/signal.c:811
 exit_to_user_mode_loop kernel/entry/common.c:161 [inline]
 exit_to_user_mode_prepare+0x1ae/0x200 kernel/entry/common.c:192
 syscall_exit_to_user_mode+0x7e/0x2e0 kernel/entry/common.c:267
 __do_fast_syscall_32+0x6c/0x90 arch/x86/entry/common.c:138
 do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:160
 entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
RIP: 0023:0xf7f41549
Code: Bad RIP value.
RSP: 002b:00000000f553b0cc EFLAGS: 00000296 ORIG_RAX: 0000000000000171
RAX: 0000000000090fc0 RBX: 0000000000000004 RCX: 0000000020f6f000
RDX: 00000000fffffea7 RSI: 0000000020000004 RDI: 0000000020b63fe4
RBP: 000000000000001c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 30131:
 kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
 kasan_set_track mm/kasan/common.c:56 [inline]
 __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:461
 slab_post_alloc_hook mm/slab.h:518 [inline]
 slab_alloc mm/slab.c:3316 [inline]
 kmem_cache_alloc+0x13a/0x3f0 mm/slab.c:3486
 dup_fd+0x89/0xc90 fs/file.c:293
 copy_files kernel/fork.c:1461 [inline]
 copy_process+0x1d99/0x6940 kernel/fork.c:2058
 _do_fork+0xe8/0xb10 kernel/fork.c:2429
 __do_sys_clone3+0x1dd/0x320 kernel/fork.c:2704
 do_syscall_32_irqs_on arch/x86/entry/common.c:78 [inline]
 __do_fast_syscall_32+0x60/0x90 arch/x86/entry/common.c:137
 do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:160
 entry_SYSENTER_compat_after_hwframe+0x4d/0x5c

The buggy address belongs to the object at ffff88805c9a00c0
 which belongs to the cache files_cache of size 832
The buggy address is located 192 bytes to the left of
 832-byte region [ffff88805c9a00c0, ffff88805c9a0400)
The buggy address belongs to the page:
page:00000000953999c6 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88805c9a0840 pfn:0x5c9a0
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea0002669748 ffffea0002a460c8 ffff88821bc47500
raw: ffff88805c9a0840 ffff88805c9a00c0 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88805c99ff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88805c99ff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88805c9a0000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
                   ^
 ffff88805c9a0080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88805c9a0100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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