From: Theodore Ts'o <tytso@xxxxxxx> commit 513f86d73855ce556ea9522b6bfd79f87356dc3a upstream. If there an inode points to a block which is also some other type of metadata block (such as a block allocation bitmap), the buffer_verified flag can be set when it was validated as that other metadata block type; however, it would make a really terrible external attribute block. The reason why we use the verified flag is to avoid constantly reverifying the block. However, it doesn't take much overhead to make sure the magic number of the xattr block is correct, and this will avoid potential crashes. This addresses CVE-2018-10879. https://bugzilla.kernel.org/show_bug.cgi?id=200001 Signed-off-by: Theodore Ts'o <tytso@xxxxxxx> Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx> Cc: stable@xxxxxxxxxx [ghackmann@xxxxxxxxxx: 3.18 backport: adjust context] Signed-off-by: Greg Hackmann <ghackmann@xxxxxxxxxx> --- fs/ext4/xattr.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c index 5b391e74c0cc..bb4faf2d0c5c 100644 --- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -218,12 +218,12 @@ ext4_xattr_check_block(struct inode *inode, struct buffer_head *bh) { int error; - if (buffer_verified(bh)) - return 0; - if (BHDR(bh)->h_magic != cpu_to_le32(EXT4_XATTR_MAGIC) || BHDR(bh)->h_blocks != cpu_to_le32(1)) return -EIO; + if (buffer_verified(bh)) + return 0; + if (!ext4_xattr_block_csum_verify(inode, bh->b_blocknr, BHDR(bh))) return -EIO; error = ext4_xattr_check_names(BFIRST(bh), bh->b_data + bh->b_size, -- 2.19.0.605.g01d371f741-goog
