2016-03-11 15:41:56

by Eryu Guan

Subject: [PATCH] ext4: fix NULL pointer dereference in ext4_mark_inode_dirty()

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

Signed-off-by: Eryu Guan <[email protected]>
---
fs/ext4/inode.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index aee960b..f1f26ea 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5261,7 +5261,7 @@ int ext4_mark_inode_dirty(handle_t *handle, struct inode *inode)
might_sleep();
trace_ext4_mark_inode_dirty(inode, _RET_IP_);
err = ext4_reserve_inode_write(handle, inode, &iloc);
- if (ext4_handle_valid(handle) &&
+ if (!err && ext4_handle_valid(handle) &&
EXT4_I(inode)->i_extra_isize < sbi->s_want_extra_isize &&
!ext4_test_inode_state(inode, EXT4_STATE_NO_EXPAND)) {
/*
--
2.5.0

2016-03-13 02:39:26

by Theodore Ts'o

Subject: Re: [PATCH] ext4: fix NULL pointer dereference in ext4_mark_inode_dirty()

On Fri, Mar 11, 2016 at 11:38:53PM +0800, Eryu Guan wrote:
> 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.

Nice catch! I'm going fix this slightly differently (although I'll
keep your description). The patch is a wee bit bigger, but the end
result is simpler to read.

Thanks,

- Ted

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ce2c4c6..b41432e 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5312,6 +5312,8 @@ int ext4_mark_inode_dirty(handle_t *handle, struct inode *inode)
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)) {
@@ -5342,9 +5344,7 @@ int ext4_mark_inode_dirty(handle_t *handle, struct inode *inode)
}
}
}
- if (!err)
- err = ext4_mark_iloc_dirty(handle, inode, &iloc);
- return err;
+ return ext4_mark_iloc_dirty(handle, inode, &iloc);
}

/*

2016-03-13 07:07:52

by Eryu Guan

Subject: Re: [PATCH] ext4: fix NULL pointer dereference in ext4_mark_inode_dirty()

On Sat, Mar 12, 2016 at 09:39:22PM -0500, Theodore Ts'o wrote:
> On Fri, Mar 11, 2016 at 11:38:53PM +0800, Eryu Guan wrote:
> > 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.
>
> Nice catch! I'm going fix this slightly differently (although I'll
> keep your description). The patch is a wee bit bigger, but the end
> result is simpler to read.

Yes, it's more easier to read. Thanks!

Eryu

>
> Thanks,
>
> - Ted
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index ce2c4c6..b41432e 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -5312,6 +5312,8 @@ int ext4_mark_inode_dirty(handle_t *handle, struct inode *inode)
> 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)) {
> @@ -5342,9 +5344,7 @@ int ext4_mark_inode_dirty(handle_t *handle, struct inode *inode)
> }
> }
> }
> - if (!err)
> - err = ext4_mark_iloc_dirty(handle, inode, &iloc);
> - return err;
> + return ext4_mark_iloc_dirty(handle, inode, &iloc);
> }
>
> /*