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SubjectRe: KASAN: use-after-free Read in fuse_dev_do_read
syzbot has found a reproducer for the following crash on:

HEAD commit: 10dc890d4228 Merge tag 'pinctrl-v4.19-3' of git://git.kern..
git tree: upstream
console output:
kernel config:
dashboard link:
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:

IMPORTANT: if you fix the bug, please add the following tag to the commit:

8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
BUG: KASAN: use-after-free in constant_test_bit
arch/x86/include/asm/bitops.h:328 [inline]
BUG: KASAN: use-after-free in fuse_dev_do_read.isra.27+0x1659/0x1920
Read of size 8 at addr ffff8801d8702630 by task syz-executor1/7794

CPU: 0 PID: 7794 Comm: syz-executor1 Not tainted 4.19.0-rc4+ #26
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+0x1c4/0x2b4 lib/dump_stack.c:113
print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
constant_test_bit arch/x86/include/asm/bitops.h:328 [inline]
fuse_dev_do_read.isra.27+0x1659/0x1920 fs/fuse/dev.c:1318
fuse_dev_read+0x1a9/0x250 fs/fuse/dev.c:1360
call_read_iter include/linux/fs.h:1802 [inline]
new_sync_read fs/read_write.c:406 [inline]
__vfs_read+0x6ac/0x9b0 fs/read_write.c:418
vfs_read+0x17f/0x3c0 fs/read_write.c:452
ksys_read+0x101/0x260 fs/read_write.c:578
__do_sys_read fs/read_write.c:588 [inline]
__se_sys_read fs/read_write.c:586 [inline]
__x64_sys_read+0x73/0xb0 fs/read_write.c:586
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
RIP: 0033:0x457679
Code: 1d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f6a5aeedc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f6a5aeee6d4 RCX: 0000000000457679
RDX: 0000000000001000 RSI: 0000000020001000 RDI: 0000000000000003
RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004d4ad0 R14: 00000000004c31e5 R15: 0000000000000000

Allocated by task 7801:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
kmem_cache_alloc+0x12e/0x730 mm/slab.c:3554
__fuse_request_alloc+0x27/0xf0 fs/fuse/dev.c:58
fuse_request_alloc+0x18/0x20 fs/fuse/dev.c:89
fuse_fill_super+0x12bf/0x1ea0 fs/fuse/inode.c:1157
mount_nodev+0x6b/0x110 fs/super.c:1204
fuse_mount+0x2c/0x40 fs/fuse/inode.c:1213
mount_fs+0xae/0x31d fs/super.c:1261
vfs_kern_mount.part.35+0xdc/0x4f0 fs/namespace.c:961
vfs_kern_mount fs/namespace.c:951 [inline]
do_new_mount fs/namespace.c:2457 [inline]
do_mount+0x581/0x31f0 fs/namespace.c:2787
ksys_mount+0x12d/0x140 fs/namespace.c:3003
__do_sys_mount fs/namespace.c:3017 [inline]
__se_sys_mount fs/namespace.c:3014 [inline]
__x64_sys_mount+0xbe/0x150 fs/namespace.c:3014
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290

Freed by task 7801:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kmem_cache_free+0x83/0x290 mm/slab.c:3756
fuse_request_free+0x8b/0xa0 fs/fuse/dev.c:104
fuse_put_request+0x2a6/0x350 fs/fuse/dev.c:304
request_end+0xba/0xaa0 fs/fuse/dev.c:414
fuse_dev_do_write+0x192e/0x36e0 fs/fuse/dev.c:1915
fuse_dev_write+0x19a/0x240 fs/fuse/dev.c:1939
call_write_iter include/linux/fs.h:1808 [inline]
new_sync_write fs/read_write.c:474 [inline]
__vfs_write+0x6b8/0x9f0 fs/read_write.c:487
vfs_write+0x1fc/0x560 fs/read_write.c:549
ksys_write+0x101/0x260 fs/read_write.c:598
__do_sys_write fs/read_write.c:610 [inline]
__se_sys_write fs/read_write.c:607 [inline]
__x64_sys_write+0x73/0xb0 fs/read_write.c:607
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290

The buggy address belongs to the object at ffff8801d8702600
which belongs to the cache fuse_request of size 448
The buggy address is located 48 bytes inside of
448-byte region [ffff8801d8702600, ffff8801d87027c0)
The buggy address belongs to the page:
page:ffffea000761c080 count:1 mapcount:0 mapping:ffff8801d4a0e240 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea0006ec0e88 ffffea0006ee91c8 ffff8801d4a0e240
raw: 0000000000000000 ffff8801d8702000 0000000100000008 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801d8702500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801d8702580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ffff8801d8702600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801d8702680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801d8702700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

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