On Nov 26, 2016, at 11:39 PM, Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
>
> i_extra_isize not divisible by 4 is problematic for several reasons:
>
> - It causes the in-inode xattr space to be misaligned, but the xattr
> header and entries are not declared __packed to express this
> possibility. This may cause poor performance or incorrect code
> generation on some platforms.
> - When validating the xattr entries we can read past the end of the
> inode if the size available for xattrs is not a multiple of 4.
> - It allows the nonsensical i_extra_isize=1, which doesn't even leave
> enough room for i_extra_isize itself.
>
> Therefore, update ext4_iget() to consider i_extra_isize not divisible by
> 4 to be an error, like the case where i_extra_isize is too large.
>
> This also matches the rule recently added to e2fsck for determining
> whether an inode has valid i_extra_isize.
>
> This patch shouldn't have any noticeable effect on
> non-corrupted/non-malicious filesystems, since the size of ext4_inode
> has always been a multiple of 4.
>
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Makes sense.
Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx>
> ---
> fs/ext4/inode.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 861f848..bc99ebe 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4564,10 +4564,12 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
> if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
> ei->i_extra_isize = le16_to_cpu(raw_inode->i_extra_isize);
> if (EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize >
> - EXT4_INODE_SIZE(inode->i_sb)) {
> - EXT4_ERROR_INODE(inode, "bad extra_isize (%u != %u)",
> - EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize,
> - EXT4_INODE_SIZE(inode->i_sb));
> + EXT4_INODE_SIZE(inode->i_sb) ||
> + (ei->i_extra_isize & 3)) {
> + EXT4_ERROR_INODE(inode,
> + "bad extra_isize %u (inode size %u)",
> + ei->i_extra_isize,
> + EXT4_INODE_SIZE(inode->i_sb));
> ret = -EFSCORRUPTED;
> goto bad_inode;
> }
> @@ -4685,6 +4687,7 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
> if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
> if (ei->i_extra_isize == 0) {
> /* The extra space is currently unused. Use it. */
> + BUILD_BUG_ON(sizeof(struct ext4_inode) & 3);
> ei->i_extra_isize = sizeof(struct ext4_inode) -
> EXT4_GOOD_OLD_INODE_SIZE;
> } else {
> --
> 2.8.0.rc3.226.g39d4020
>
Cheers, Andreas
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