This is a note to let you know that I've just added the patch titled
ext4: fix crash when a directory's i_size is too small
to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: ext4-fix-crash-when-a-directory-s-i_size-is-too-small.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 stable@vger.kernel.org know about it.
From 9d5afec6b8bd46d6ed821aa1579634437f58ef1f Mon Sep 17 00:00:00 2001
From: Chandan Rajendra chandan@linux.vnet.ibm.com Date: Mon, 11 Dec 2017 15:00:57 -0500 Subject: ext4: fix crash when a directory's i_size is too small
From: Chandan Rajendra chandan@linux.vnet.ibm.com
commit 9d5afec6b8bd46d6ed821aa1579634437f58ef1f upstream.
On a ppc64 machine, when mounting a fuzzed ext2 image (generated by fsfuzzer) the following call trace is seen,
VFS: brelse: Trying to free free buffer WARNING: CPU: 1 PID: 6913 at /root/repos/linux/fs/buffer.c:1165 .__brelse.part.6+0x24/0x40 .__brelse.part.6+0x20/0x40 (unreliable) .ext4_find_entry+0x384/0x4f0 .ext4_lookup+0x84/0x250 .lookup_slow+0xdc/0x230 .walk_component+0x268/0x400 .path_lookupat+0xec/0x2d0 .filename_lookup+0x9c/0x1d0 .vfs_statx+0x98/0x140 .SyS_newfstatat+0x48/0x80 system_call+0x58/0x6c
This happens because the directory that ext4_find_entry() looks up has inode->i_size that is less than the block size of the filesystem. This causes 'nblocks' to have a value of zero. ext4_bread_batch() ends up not reading any of the directory file's blocks. This renders the entries in bh_use[] array to continue to have garbage data. buffer_uptodate() on bh_use[0] can then return a zero value upon which brelse() function is invoked.
This commit fixes the bug by returning -ENOENT when the directory file has no associated blocks.
Reported-by: Abdul Haleem abdhalee@linux.vnet.ibm.com Signed-off-by: Chandan Rajendra chandan@linux.vnet.ibm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/ext4/namei.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/fs/ext4/namei.c +++ b/fs/ext4/namei.c @@ -1403,6 +1403,10 @@ static struct buffer_head * ext4_find_en "falling back\n")); } nblocks = dir->i_size >> EXT4_BLOCK_SIZE_BITS(sb); + if (!nblocks) { + ret = NULL; + goto cleanup_and_exit; + } start = EXT4_I(dir)->i_dir_start_lookup; if (start >= nblocks) start = 0;
Patches currently in stable-queue which might be from chandan@linux.vnet.ibm.com are
queue-4.4/ext4-fix-crash-when-a-directory-s-i_size-is-too-small.patch