ext4: verify the depth of extent tree in ext4_find_extent()

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

diff --git a/fs/ext4/ext4_extents.h b/fs/ext4/ext4_extents.h
index 98fb0c119c6827dd50b86ac3521f216bba41170c..adf6668b596f9e20aab3878b791009bfa5f051a0 100644 (file)
--- a/fs/ext4/ext4_extents.h
+++ b/fs/ext4/ext4_extents.h
@@ -91,6 +91,7 @@ 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) + \

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index c969275ce3ee7469167a6921e8fa22e4c91ed3a2..08226f72b7ee4bc23089449a8e5f4b15e0ee90f0 100644 (file)
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -869,6 +869,12 @@ ext4_find_extent(struct inode *inode, ext4_lblk_t block,
 
        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);