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>
---
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
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