Patch "ext4: fix NULL pointer dereference in ext4_mark_inode_dirty()" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

ext4: fix NULL pointer dereference in ext4_mark_inode_dirty()

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ext4-fix-null-pointer-dereference-in-ext4_mark_inode_dirty.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eryu Guan <[email protected]>
Date: Sat, 12 Mar 2016 21:40:32 -0500
Subject: ext4: fix NULL pointer dereference in ext4_mark_inode_dirty()

From: Eryu Guan <[email protected]>

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 ]

---
 fs/ext4/inode.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

@@ -5109,6 +5109,8 @@ 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)) {

@@ -5139,9 +5141,7 @@ 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);
 }
 
 /*

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/ext4-fix-null-pointer-dereference-in-ext4_mark_inode_dirty.patch