For leaf dir, there should be as many bestfree slots as there are dir data
blocks that can fit under i_size. Othrewise, which may cause UAF or
slab-out-of bound etc.
Root cause is we don't examin the number bestfree slots, when the slots
number less than dir data blocks, if we need to allocate new dir data block
and update the bestfree array, we will use the dir block number as index to
assign bestfree array, which may cause UAF or other memory access problem.
This issue can also triggered with test cases xfs/473 from fstests.
Simplify the testcase xfs/473 with commands below:
DEV=/dev/sdb
MP=/mnt/sdb
WORKDIR=/mnt/sdb/341 #1. mkfs create new xfs image
mkfs.xfs -f ${DEV}
mount ${DEV} ${MP}
mkdir -p ${WORKDIR}
for i in `seq 1 341` #2. create leaf dir with 341 entries file name len 8
do
touch ${WORKDIR}/$(printf "%08d" ${i})
done
inode=$(ls -i ${MP} | cut -d' ' -f1)
umount ${MP} #3. xfs_db set bestcount to 0
xfs_db -x ${DEV} -c "inode ${inode}" -c "dblock 8388608" \
-c "write ltail.bestcount 0"
mount ${DEV} ${MP}
touch ${WORKDIR}/{1..100}.txt #4. touch new file, reproduce
The error log is shown as follows:
==================================================================
BUG: KASAN: use-after-free in xfs_dir2_leaf_addname+0x1995/0x1ac0
Write of size 2 at addr ffff88810168b000 by task touch/1552
CPU: 5 PID: 1552 Comm: touch Not tainted 6.0.0-rc3+ #101
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x4d/0x66
print_report.cold+0xf6/0x691
kasan_report+0xa8/0x120
xfs_dir2_leaf_addname+0x1995/0x1ac0
xfs_dir_createname+0x58c/0x7f0
xfs_create+0x7af/0x1010
xfs_generic_create+0x270/0x5e0
path_openat+0x270b/0x3450
do_filp_open+0x1cf/0x2b0
do_sys_openat2+0x46b/0x7a0
do_sys_open+0xb7/0x130
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7fe4d9e9312b
Code: 25 00 00 41 00 3d 00 00 41 00 74 4b 64 8b 04 25 18 00 00 00 85 c0
75 67 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00
f0 ff ff 0f 87 91 00 00 00 48 8b 4c 24 28 64 48 33 0c 25
RSP: 002b:00007ffda4c16c20 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007fe4d9e9312b
RDX: 0000000000000941 RSI: 00007ffda4c17f33 RDI: 00000000ffffff9c
RBP: 00007ffda4c17f33 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000000001b6 R11: 0000000000000246 R12: 0000000000000941
R13: 00007fe4d9f631a4 R14: 00007ffda4c17f33 R15: 0000000000000000
</TASK>
The buggy address belongs to the physical page:
page:ffffea000405a2c0 refcount:0 mapcount:0 mapping:0000000000000000
index:0x0 pfn:0x10168b
flags: 0x2fffff80000000(node=0|zone=2|lastcpupid=0x1fffff)
raw: 002fffff80000000 ffffea0004057788 ffffea000402dbc8 0000000000000000
raw: 0000000000000000 0000000000170000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff88810168af00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88810168af80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88810168b000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff88810168b080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff88810168b100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
Disabling lock debugging due to kernel taint
00000000: 58 44 44 33 5b 53 35 c2 00 00 00 00 00 00 00 78
XDD3[S5........x
XFS (sdb): Internal error xfs_dir2_data_use_free at line 1200 of file
fs/xfs/libxfs/xfs_dir2_data.c. Caller
xfs_dir2_data_use_free+0x28a/0xeb0
CPU: 5 PID: 1552 Comm: touch Tainted: G B 6.0.0-rc3+
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x4d/0x66
xfs_corruption_error+0x132/0x150
xfs_dir2_data_use_free+0x198/0xeb0
xfs_dir2_leaf_addname+0xa59/0x1ac0
xfs_dir_createname+0x58c/0x7f0
xfs_create+0x7af/0x1010
xfs_generic_create+0x270/0x5e0
path_openat+0x270b/0x3450
do_filp_open+0x1cf/0x2b0
do_sys_openat2+0x46b/0x7a0
do_sys_open+0xb7/0x130
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7fe4d9e9312b
Code: 25 00 00 41 00 3d 00 00 41 00 74 4b 64 8b 04 25 18 00 00 00 85 c0
75 67 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00
f0 ff ff 0f 87 91 00 00 00 48 8b 4c 24 28 64 48 33 0c 25
RSP: 002b:00007ffda4c16c20 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007fe4d9e9312b
RDX: 0000000000000941 RSI: 00007ffda4c17f46 RDI: 00000000ffffff9c
RBP: 00007ffda4c17f46 R08: 0000000000000000 R09: 0000000000000001
R10: 00000000000001b6 R11: 0000000000000246 R12: 0000000000000941
R13: 00007fe4d9f631a4 R14: 00007ffda4c17f46 R15: 0000000000000000
</TASK>
XFS (sdb): Corruption detected. Unmount and run xfs_repair
Signed-off-by: Guo Xuenan <guoxuenan@xxxxxxxxxx>
---
fs/xfs/libxfs/xfs_dir2_leaf.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/fs/xfs/libxfs/xfs_dir2_leaf.c b/fs/xfs/libxfs/xfs_dir2_leaf.c
index d9b66306a9a7..09414651ac48 100644
--- a/fs/xfs/libxfs/xfs_dir2_leaf.c
+++ b/fs/xfs/libxfs/xfs_dir2_leaf.c
@@ -659,6 +659,20 @@ xfs_dir2_leaf_addname(
bestsp = xfs_dir2_leaf_bests_p(ltp);
length = xfs_dir2_data_entsize(dp->i_mount, args->namelen);
+ /*
+ * There should be as many bestfree slots as there are dir data
+ * blocks that can fit under i_size. Othrewise, which may cause
+ * serious problems eg. UAF or slab-out-of bound etc.
+ */
+ if (be32_to_cpu(ltp->bestcount) !=
+ xfs_dir2_byte_to_db(args->geo, dp->i_d.di_size)) {
+ xfs_buf_ioerror_alert(lbp, __return_address);
+ if (tp->t_flags & XFS_TRANS_DIRTY)
+ xfs_force_shutdown(tp->t_mountp,
+ SHUTDOWN_CORRUPT_INCORE);
+ return -EFSCORRUPTED;
+ }
+
/*
* See if there are any entries with the same hash value
* and space in their block for the new entry.
--
2.25.1
