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BUG: KASAN: slab-out-of-bounds in fscache_set_key fs/fscache/cookie.c:120 [inline]
BUG: KASAN: slab-out-of-bounds in fscache_alloc_cookie+0x745/0x800 fs/fscache/cookie.c:171
Read of size 4 at addr ffff8801bcb02210 by task syz-executor1/8390

CPU: 1 PID: 8390 Comm: syz-executor1 Not tainted 4.19.0-rc7-next-20181012+ #93
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+0x244/0x3ab lib/dump_stack.c:113
 print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
 fscache_set_key fs/fscache/cookie.c:120 [inline]
 fscache_alloc_cookie+0x745/0x800 fs/fscache/cookie.c:171
 __fscache_acquire_cookie+0x230/0xb60 fs/fscache/cookie.c:303
 fscache_acquire_cookie include/linux/fscache.h:338 [inline]
 v9fs_cache_session_get_cookie+0xc4/0x270 fs/9p/cache.c:73
 v9fs_session_init+0x10e4/0x1bb0 fs/9p/v9fs.c:485
 v9fs_mount+0x7c/0x8f0 fs/9p/vfs_super.c:135
 legacy_get_tree+0x131/0x460 fs/fs_context.c:718
 vfs_get_tree+0x1cb/0x5c0 fs/super.c:1795
 do_new_mount fs/namespace.c:2648 [inline]
 do_mount+0x70c/0x1d90 fs/namespace.c:2974
 ksys_mount+0x12d/0x140 fs/namespace.c:3190
 __do_sys_mount fs/namespace.c:3204 [inline]
 __se_sys_mount fs/namespace.c:3201 [inline]
 __x64_sys_mount+0xbe/0x150 fs/namespace.c:3201
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457569
Code: fd b3 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 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f72fe6dac78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000457569
RDX: 0000000020000040 RSI: 0000000020000000 RDI: 0000000000000000
RBP: 000000000072bf00 R08: 0000000020000080 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f72fe6db6d4
R13: 00000000004c28a1 R14: 00000000004d3c90 R15: 00000000ffffffff

Allocated by task 8390:
 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
 __do_kmalloc mm/slab.c:3722 [inline]
 __kmalloc+0x15b/0x760 mm/slab.c:3731
 kmalloc include/linux/slab.h:551 [inline]
 kzalloc include/linux/slab.h:741 [inline]
 fscache_set_key fs/fscache/cookie.c:101 [inline]
 fscache_alloc_cookie+0x68f/0x800 fs/fscache/cookie.c:171
 __fscache_acquire_cookie+0x230/0xb60 fs/fscache/cookie.c:303
 fscache_acquire_cookie include/linux/fscache.h:338 [inline]
 v9fs_cache_session_get_cookie+0xc4/0x270 fs/9p/cache.c:73
 v9fs_session_init+0x10e4/0x1bb0 fs/9p/v9fs.c:485
 v9fs_mount+0x7c/0x8f0 fs/9p/vfs_super.c:135
 legacy_get_tree+0x131/0x460 fs/fs_context.c:718
 vfs_get_tree+0x1cb/0x5c0 fs/super.c:1795
 do_new_mount fs/namespace.c:2648 [inline]
 do_mount+0x70c/0x1d90 fs/namespace.c:2974
 ksys_mount+0x12d/0x140 fs/namespace.c:3190
 __do_sys_mount fs/namespace.c:3204 [inline]
 __se_sys_mount fs/namespace.c:3201 [inline]
 __x64_sys_mount+0xbe/0x150 fs/namespace.c:3201
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff8801bcb02200
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 16 bytes inside of
 32-byte region [ffff8801bcb02200, ffff8801bcb02220)
The buggy address belongs to the page:
page:ffffea0006f2c080 count:1 mapcount:0 mapping:ffff8801da8001c0 index:0xffff8801bcb02fc1
flags: 0x2fffc0000000200(slab)
raw: 02fffc0000000200 ffffea00073a45c8 ffffea00070e6688 ffff8801da8001c0
raw: ffff8801bcb02fc1 ffff8801bcb02000 000000010000003f 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801bcb02100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801bcb02180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801bcb02200: 00 00 02 fc fc fc fc fc 00 00 03 fc fc fc fc fc
                         ^
 ffff8801bcb02280: 00 00 00 00 fc fc fc fc fb fb fb fb fc fc fc fc
 ffff8801bcb02300: fb fb fb fb fc fc fc fc 05 fc fc fc fc fc fc fc
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