linux-ext4 - [PATCH] ext4: verify the depth of extent tree in ext4_find

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Message-Id: <20180614234454.25664-1-tytso@mit.edu>
Date:   Thu, 14 Jun 2018 19:44:54 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:     wen.xu@...ech.edu, Theodore Ts'o <tytso@....edu>
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.

https://bugzilla.kernel.org/show_bug.cgi?id=199417

Signed-off-by: Theodore Ts'o <tytso@....edu>
---
 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);
-- 
2.18.0.rc0