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Subject[PATCH 3.2 084/115] ext4: fix NULL pointer dereference in ext4_mark_inode_dirty()
3.2.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eryu Guan <guaneryu@gmail.com>

commit 5e1021f2b6dff1a86a468a1424d59faae2bc63c1 upstream.

ext4_reserve_inode_write() in ext4_mark_inode_dirty() could fail on
error (e.g. EIO) and iloc.bh can be NULL in this case. But the error is
ignored in the following "if" condition and ext4_expand_extra_isize()
might be called with NULL iloc.bh set, which triggers NULL pointer
dereference.

This is uncovered by commit 8b4953e13f4c ("ext4: reserve code points for
the project quota feature"), which enlarges the ext4_inode size, and
run the following script on new kernel but with old mke2fs:

#/bin/bash
mnt=/mnt/ext4
devname=ext4-error
dev=/dev/mapper/$devname
fsimg=/home/fs.img

trap cleanup 0 1 2 3 9 15

cleanup()
{
umount $mnt >/dev/null 2>&1
dmsetup remove $devname
losetup -d $backend_dev
rm -f $fsimg
exit 0
}

rm -f $fsimg
fallocate -l 1g $fsimg
backend_dev=`losetup -f --show $fsimg`
devsize=`blockdev --getsz $backend_dev`

good_tab="0 $devsize linear $backend_dev 0"
error_tab="0 $devsize error $backend_dev 0"

dmsetup create $devname --table "$good_tab"

mkfs -t ext4 $dev
mount -t ext4 -o errors=continue,strictatime $dev $mnt

dmsetup load $devname --table "$error_tab" && dmsetup resume $devname
echo 3 > /proc/sys/vm/drop_caches
ls -l $mnt
exit 0

[ Patch changed to simplify the function a tiny bit. -- Ted ]

Signed-off-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/ext4/inode.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4636,6 +4636,8 @@ int ext4_mark_inode_dirty(handle_t *hand
might_sleep();
trace_ext4_mark_inode_dirty(inode, _RET_IP_);
err = ext4_reserve_inode_write(handle, inode, &iloc);
+ if (err)
+ return err;
if (ext4_handle_valid(handle) &&
EXT4_I(inode)->i_extra_isize < sbi->s_want_extra_isize &&
!ext4_test_inode_state(inode, EXT4_STATE_NO_EXPAND)) {
@@ -4666,9 +4668,7 @@ int ext4_mark_inode_dirty(handle_t *hand
}
}
}
- if (!err)
- err = ext4_mark_iloc_dirty(handle, inode, &iloc);
- return err;
+ return ext4_mark_iloc_dirty(handle, inode, &iloc);
}

/*
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