-------- =D0=98=D1=81=D1=85=D0=BE=D0=B4=D0=BD=D0=BE=D0=B5 =D1=81=D0= =BE=D0=BE=D0=B1=D1=89=D0=B5=D0=BD=D0=B8=D0=B5 --------
=D0= =A2=D0=B5=D0=BC=D0=B0:	f2fs: Possible use-after-free when umount filesystem
=D0= =94=D0=B0=D1=82=D0=B0:	Mon, 21 Jul 2014 14:56:44 +0400
=D0= =9E=D1=82:	Andrey Tsyvarev <tsyvarev@ispras.ru>
=D0= =9A=D0=BE=D0=BC=D1=83:	Jaegeuk Kim <jaegeuk.kim@samsung.com>
=D0= =9A=D0=BE=D0=BF=D0=B8=D1=8F:	linux-f2fs-devel@lists.sourceforge.ne= t, linux-kernel <linux-kernel@vger.kernel.org>, Alexey Kho= roshilov <khoroshilov@ispras.ru>
Hello,

Using memory error detector reveals the following use-after-free error=20
in 3.15.0:

AddressSanitizer: heap-use-after-free in f2fs_evict_inode
Read of size 8 by thread T22279:
 [<ffffffffa02d8702>] f2fs_evict_inode+0x102/0x2e0 [f2fs]=20
/home/tester/linux-sources/linux-kasan/fs/f2fs/f2fs.h:584
 [<ffffffff812359af>] evict+0x15f/0x290=20
/home/tester/linux-sources/linux-kasan/fs/inode.c:550
 [<     inlined    >] iput+0x196/0x280 iput_final=20
/home/tester/linux-sources/linux-kasan/fs/inode.c:1418
 [<ffffffff812369a6>] iput+0x196/0x280=20
/home/tester/linux-sources/linux-kasan/fs/inode.c:1436
 [<ffffffffa02dc416>] f2fs_put_super+0xd6/0x170 [f2fs]=20
/home/tester/linux-sources/linux-kasan/fs/f2fs/super.c:434
 [<ffffffff81210095>] generic_shutdown_super+0xc5/0x1b0=20
/home/tester/linux-sources/linux-kasan/fs/super.c:406
 [<ffffffff812105fd>] kill_block_super+0x4d/0xb0=20
/home/tester/linux-sources/linux-kasan/fs/super.c:1019
 [<ffffffff81210a86>] deactivate_locked_super+0x66/0x80=20
/home/tester/linux-sources/linux-kasan/fs/super.c:284
 [<ffffffff81211c98>] deactivate_super+0x68/0x80=20
/home/tester/linux-sources/linux-kasan/fs/super.c:307
 [<ffffffff8123cc88>] mntput_no_expire+0x198/0x250=20
/home/tester/linux-sources/linux-kasan/fs/namespace.c:986 (discriminator =
3)
 [<     inlined    >] SyS_umount+0xe9/0x1a0 SYSC_umount=20
/home/tester/linux-sources/linux-kasan/fs/namespace.c:1424
 [<ffffffff8123f1c9>] SyS_umount+0xe9/0x1a0=20
/home/tester/linux-sources/linux-kasan/fs/namespace.c:1392
 [<ffffffff81cc8df9>] system_call_fastpath+0x16/0x1b=20
/home/tester/linux-sources/linux-kasan/arch/x86/kernel/entry_64.S:426

Freed by thread T3:
 [<ffffffffa02dc337>] f2fs_i_callback+0x27/0x30 [f2fs]=20
/home/tester/linux-sources/linux-kasan/fs/f2fs/super.c:408
 [<     inlined    >] rcu_process_callbacks+0x2d6/0x930 __rcu_recla=
im=20
/home/tester/linux-sources/linux-kasan/kernel/rcu/rcu.h:114
 [<     inlined    >] rcu_process_callbacks+0x2d6/0x930 rcu_do_batc=
h=20
/home/tester/linux-sources/linux-kasan/kernel/rcu/tree.c:2242
 [<     inlined    >] rcu_process_callbacks+0x2d6/0x930=20
invoke_rcu_callbacks=20
/home/tester/linux-sources/linux-kasan/kernel/rcu/tree.c:2499
 [<     inlined    >] rcu_process_callbacks+0x2d6/0x930=20
__rcu_process_callbacks=20
/home/tester/linux-sources/linux-kasan/kernel/rcu/tree.c:2466
 [<ffffffff810fd266>] rcu_process_callbacks+0x2d6/0x930=20
/home/tester/linux-sources/linux-kasan/kernel/rcu/tree.c:2483
 [<ffffffff8107cce2>] __do_softirq+0x142/0x380=20
/home/tester/linux-sources/linux-kasan/kernel/softirq.c:269
 [<ffffffff8107cf50>] run_ksoftirqd+0x30/0x50=20
/home/tester/linux-sources/linux-kasan/kernel/softirq.c:658
 [<ffffffff810b2a87>] smpboot_thread_fn+0x197/0x280=20
/home/tester/linux-sources/linux-kasan/kernel/smpboot.c:160
 [<ffffffff810a8238>] kthread+0x148/0x160=20
/home/tester/linux-sources/linux-kasan/kernel/kthread.c:207
 [<ffffffff81cc8d4c>] ret_from_fork+0x7c/0xb0=20
/home/tester/linux-sources/linux-kasan/arch/x86/kernel/entry_64.S:351

Allocated by thread T22276:
 [<ffffffffa02dc7dd>] f2fs_alloc_inode+0x2d/0x170 [f2fs]=20
/home/tester/linux-sources/linux-kasan/fs/f2fs/super.c:356
 [<ffffffff8123471d>] alloc_inode+0x2d/0xe0=20
/home/tester/linux-sources/linux-kasan/fs/inode.c:208
 [<ffffffff81235e2a>] iget_locked+0x10a/0x230=20
/home/tester/linux-sources/linux-kasan/fs/inode.c:1085
 [<ffffffffa02d7495>] f2fs_iget+0x35/0xa80 [f2fs]=20
/home/tester/linux-sources/linux-kasan/fs/f2fs/inode.c:129
 [<ffffffffa02e2393>] f2fs_fill_super+0xb53/0xff0 [f2fs]=20
/home/tester/linux-sources/linux-kasan/fs/f2fs/super.c:1021
 [<ffffffff81211bce>] mount_bdev+0x1de/0x240=20
/home/tester/linux-sources/linux-kasan/fs/super.c:992
 [<ffffffffa02dbce0>] f2fs_mount+0x10/0x20 [f2fs]=20
/home/tester/linux-sources/linux-kasan/fs/f2fs/super.c:1127
 [<ffffffff81212a85>] mount_fs+0x55/0x220=20
/home/tester/linux-sources/linux-kasan/fs/super.c:1095
 [<ffffffff8123c026>] vfs_kern_mount+0x66/0x200=20
/home/tester/linux-sources/linux-kasan/fs/namespace.c:851
 [<     inlined    >] do_mount+0x2b4/0x1120 do_new_mount=20
/home/tester/linux-sources/linux-kasan/fs/namespace.c:2129
 [<ffffffff812400d4>] do_mount+0x2b4/0x1120=20
/home/tester/linux-sources/linux-kasan/fs/namespace.c:2453
 [<     inlined    >] SyS_mount+0xb2/0x110 SYSC_mount=20
/home/tester/linux-sources/linux-kasan/fs/namespace.c:2647
 [<ffffffff812414a2>] SyS_mount+0xb2/0x110=20
/home/tester/linux-sources/linux-kasan/fs/namespace.c:2620
 [<ffffffff81cc8df9>] system_call_fastpath+0x16/0x1b=20
/home/tester/linux-sources/linux-kasan/arch/x86/kernel/entry_64.S:426

The buggy address ffff8800587866c8 is located 48 bytes inside
 of 680-byte region [ffff880058786698, ffff880058786940)

Memory state around the buggy address:
 ffff880058786100: ffffffff ffffffff ffffffff ffffffff
 ffff880058786200: ffffffff ffffffff ffffffrr rrrrrrrr
 ffff880058786300: rrrrrrrr rrffffff ffffffff ffffffff
 ffff880058786400: ffffffff ffffffff ffffffff ffffffff
 ffff880058786500: ffffffff ffffffff ffffffff fffffffr
>ffff880058786600: rrrrrrrr rrrrrrrr rrrfffff ffffffff
                                               ^
 ffff880058786700: ffffffff ffffffff ffffffff ffffffff
 ffff880058786800: ffffffff ffffffff ffffffff ffffffff
 ffff880058786900: ffffffff rrrrrrrr rrrrrrrr rrrr....
 ffff880058786a00: ........ ........ ........ ........
 ffff880058786b00: ........ ........ ........ ........
Legend:
 f - 8 freed bytes
 r - 8 redzone bytes
 . - 8 allocated bytes
 x=3D1..7 - x allocated bytes + (8-x) redzone bytes


Investigation shows, that f2fs_evict_inode, when called for=20
'meta_inode', uses invalidate_mapping_pages() for 'node_inode'.
But 'node_inode' is deleted before 'meta_inode' in f2fs_put_super via=20
iput().

It seems that in common usage scenario this use-after-free is benign,=20
because 'node_inode' remains partially valid data even after=20
kmem_cache_free().
But things may change if, while 'meta_inode' is evicted in one f2fs=20
filesystem, another (mounted) f2fs filesystem requests inode from cache,=20
and formely
'node_inode' of the first filesystem is returned.


Found by Linux File System Verification project (linuxtesting.org).


--=20
Best regards,



Andrey Tsyvarev



Linux Verification Center, ISPRAS



web:h=
ttp://linuxtesting.org