CVE-2019-13104: ext4: check for underflow in ext4fs_read_file

in ext4fs_read_file, it is possible for a broken/malicious file system to cause a memcpy of a negative number of bytes, which overflows all memory. This patch fixes the issue by checking for a negative length. Signed-off-by: Paul Emge <[email protected]>
grygoriyS · Jul 18, 2019 · 878269d · 878269d
1 parent 6e5a79d
commit 878269d
Showing 1 changed file with 5 additions and 3 deletions.
diff --git a/fs/ext4/ext4fs.c b/fs/ext4/ext4fs.c
@@ -66,13 +66,15 @@ int ext4fs_read_file(struct ext2fs_node *node, loff_t pos,
 
 	ext_cache_init(&cache);
 
-	if (blocksize <= 0)
-		return -1;
-
 	/* Adjust len so it we can't read past the end of the file. */
 	if (len + pos > filesize)
 		len = (filesize - pos);
 
+	if (blocksize <= 0 || len <= 0) {
+		ext_cache_fini(&cache);
+		return -1;
+	}
+
 	blockcnt = lldiv(((len + pos) + blocksize - 1), blocksize);
 
 	for (i = lldiv(pos, blocksize); i < blockcnt; i++) {