From bc890a60247171294acc0bd67d211fa4b88d40ba Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@mit.edu>
Date: Thu, 14 Jun 2018 12:55:10 -0400
Subject: [PATCH] ext4: verify the depth of extent tree in ext4_find_extent()
Git-commit: bc890a60247171294acc0bd67d211fa4b88d40ba
Patch-mainline: v4.18-rc4
References: bsc#1099846 cve-2018-10877
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
Acked-by: Jan Kara <jack@suse.cz>
---
fs/ext4/ext4_extents.h | 1 +
fs/ext4/extents.c | 6 ++++++
2 files changed, 7 insertions(+)
diff --git a/fs/ext4/ext4_extents.h b/fs/ext4/ext4_extents.h
index 98fb0c119c68..adf6668b596f 100644
--- 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 c969275ce3ee..08226f72b7ee 100644
--- 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);
--
2.16.4