ext4: CVE-2018-10877

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

References:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=bc890a60247171294acc0bd67d211fa4b88d40ba

Signed-off-by: Andreas Wellving <andreas.wellving@enea.com>

Change-Id: I688e9ce0a02f48c45f3cfa3259fa62a4b93532e6

2 files changed, 55 insertions, 0 deletions

diff --git a/patches/cve/4.9.x.scc b/patches/cve/4.9.x.scc
index 959c87b..c774696 100644
--- a/patches/cve/4.9.x.scc
+++ b/patches/cve/4.9.x.scc
@@ -28,3 +28,4 @@ patch CVE-2018-9518-NFC-llcp-Limit-size-of-SDP-URI.patch
 
 #CVEs fixed in 4.9.112:
 patch CVE-2018-10876-ext4-only-look-at-the-bg_flags-field-if-it-is-valid.patch
+patch CVE-2018-10877-ext4-verify-the-depth-of-extent-tree-in-ext4_find_ex.patch
diff --git a/patches/cve/CVE-2018-10877-ext4-verify-the-depth-of-extent-tree-in-ext4_find_ex.patch b/patches/cve/CVE-2018-10877-ext4-verify-the-depth-of-extent-tree-in-ext4_find_ex.patch
new file mode 100644
index 0000000..cade63f
--- /dev/null
+++ b/patches/cve/CVE-2018-10877-ext4-verify-the-depth-of-extent-tree-in-ext4_find_ex.patch
@@ -0,0 +1,54 @@
+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()
+
+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.
+Upstream-Status: Backport
+
+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: Andreas Wellving <andreas.wellving@enea.com>
+---
+ 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 98fb0c1..adf6668 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 c969275..08226f7 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);
+-- 
+
+