4.9-stable review patch. If anyone has any objections, please let me know.
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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 @@ -1417,6 +1417,10 @@ 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;