ext4: verify the depth of extent tree in ext4_find_extent()
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>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/fs/ext4/ext4_extents.h b/fs/ext4/ext4_extents.h
index 3c93815..2d8e737 100644
--- a/fs/ext4/ext4_extents.h
+++ b/fs/ext4/ext4_extents.h
@@ -103,6 +103,7 @@
};
#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) + \
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 551353b..920453b 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -868,6 +868,12 @@
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 = -EFSCORRUPTED;
+ goto err;
+ }
if (path) {
ext4_ext_drop_refs(path);
