[PATCH 3.18 064/120] ext4: verify the depth of extent tree in ext4_find_extent()

Greg Kroah-Hartman
2018-10-11T15:39:22Z

From: Theodore Ts'o <tytso@mit.edu>

commit bc890a60247171294acc0bd67d211fa4b88d40ba upstream.

If there is a corupted file system where the claimed depth of the
extent tree is -1, this can cause a massive buffer overrun leading to
sadness.

This addresses CVE-2018-10877.

https://bugzilla.kernel.org/show_bug.cgi?id=199417

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[bwh: Backported to 3.16: return -EIO instead of -EFSCORRUPTED]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/ext4/ext4_extents.h | 1 +
fs/ext4/extents.c | 6 ++++++
2 files changed, 7 insertions(+)

--- a/fs/ext4/ext4_extents.h
+++ b/fs/ext4/ext4_extents.h
@@ -103,6 +103,7 @@ struct ext4_extent_header {
};

#define EXT4_EXT_MAGIC cpu_to_le16(0xf30a)
+#define EXT4_MAX_EXTENT_DEPTH 5

#define EXT4_EXTENT_TAIL_OFFSET(hdr) \
(sizeof(struct ext4_extent_header) + \
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -870,6 +870,12 @@ ext4_find_extent(struct inode *inode, ex

eh = ext_inode_hdr(inode);
depth = ext_depth(inode);
+ if (depth < 0 || depth > EXT4_MAX_EXTENT_DEPTH) {
+ EXT4_ERROR_INODE(inode, "inode has invalid extent depth: %d",
+ depth);
+ ret = -EIO;
+ goto err;
+ }

if (path) {
ext4_ext_drop_refs(path);