[PATCH 3.16 079/366] ext4: don't read out of bounds when checking for in-inode xattrs

Ben Hutchings
2018-11-11T20:13:12Z

From: Eric Biggers <ebiggers@google.com>

commit 290ab230016f187c3551d8380ea742889276d03a upstream.

With i_extra_isize equal to or close to the available space, it was
possible for us to read past the end of the inode when trying to detect
or validate in-inode xattrs. Fix this by checking for the needed extra
space first.

This patch shouldn't have any noticeable effect on
non-corrupted/non-malicious filesystems.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/ext4/inode.c | 4 +++-
fs/ext4/xattr.c | 5 ++---
2 files changed, 5 insertions(+), 4 deletions(-)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4165,7 +4165,9 @@ static inline void ext4_iget_extra_inode
{
__le32 *magic = (void *)raw_inode +
EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize;
- if (*magic == cpu_to_le32(EXT4_XATTR_MAGIC)) {
+ if (EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize + sizeof(__le32) <=
+ EXT4_INODE_SIZE(inode->i_sb) &&
+ *magic == cpu_to_le32(EXT4_XATTR_MAGIC)) {
ext4_set_inode_state(inode, EXT4_STATE_XATTR);
ext4_find_inline_data_nolock(inode);
} else
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -247,13 +247,12 @@ static int
__xattr_check_inode(struct inode *inode, struct ext4_xattr_ibody_header *header,
void *end, const char *function, unsigned int line)
{
- struct ext4_xattr_entry *entry = IFIRST(header);
int error = -EIO;

- if (((void *) header >= end) ||
+ if (end - (void *)header < sizeof(*header) + sizeof(u32) ||
(header->h_magic != cpu_to_le32(EXT4_XATTR_MAGIC)))
goto errout;
- error = ext4_xattr_check_names(entry, end, entry);
+ error = ext4_xattr_check_names(IFIRST(header), end, IFIRST(header));
errout:
if (error)
__ext4_error_inode(inode, function, line, 0,