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From d69a9df614fc68741efcb0fcc020f05caa99d668 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()
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
CVE: CVE-2018-10877
Upstream-Status: Backport [https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.14.y&id=d69a9df614fc68741efcb0fcc020f05caa99d668]
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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 8ecf84b8f5a1..a284fb28944b 100644
--- 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 883e89a903d1..5592b7726241 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -881,6 +881,12 @@ 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);
--
2.20.1
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