4.9-stable review patch. If anyone has any objections, please let me know.
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From: Theodore Ts'o tytso@mit.edu
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@mit.edu Reviewed-by: Andreas Dilger adilger@dilger.ca [Backported to 4.9: adjust context] Signed-off-by: Daniel Rosenberg drosen@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/ext4/xattr.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -209,12 +209,12 @@ ext4_xattr_check_block(struct inode *ino { 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 -EFSCORRUPTED; + if (buffer_verified(bh)) + return 0; + if (!ext4_xattr_block_csum_verify(inode, bh)) return -EFSBADCRC; error = ext4_xattr_check_names(BFIRST(bh), bh->b_data + bh->b_size,