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>
(cherry picked from commit d69a9df614fc68741efcb0fcc020f05caa99d668)

Orabug: 29396712
CVE:CVE-2018-10877

Signed-off-by: John Donnelly <John.P.Donnelly@oracle.com>
Reviewed-by: Somasundaram Krishnasamy <somasundaram.krishnasamy@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>

diff --git a/fs/ext4/ext4_extents.h b/fs/ext4/ext4_extents.h
index 3c938154709478ba39f5eb18d8d2b53678932ee8..2d8e737935121b1ba1b13ddf1779ddb0ab4b98d6 100644 (file)
--- 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) + \

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 937798ef50f25781282adee0b3568773a8412c93..9c41d296fab2e811d71d0e008703e1f7ca56882f 100644 (file)
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -874,6 +874,12 @@ 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);