libext2fs: add check for too-short directory blocks

If there is an inline data directory which is smaller than 8 bytes
(which should never happen but for corrupted or fuzzed file systems),
ext2fs_process_dir_block() will now abort EXT2_ET_DIR_CORRUPTED to
avoid an out-of-bounds read.

Reported-by: Nils Bars <nils.bars@rub.de>
Reported-by: Moritz Schlögel <moritz.schloegel@rub.de>
Reported-by: Nico Schiller <nico.schiller@rub.de>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/lib/ext2fs/dir_iterate.c b/lib/ext2fs/dir_iterate.c
index b2b7769..7798a48 100644 (file)
--- a/lib/ext2fs/dir_iterate.c
+++ b/lib/ext2fs/dir_iterate.c
@@ -221,6 +221,10 @@ int ext2fs_process_dir_block(ext2_filsys fs,
        if (ext2fs_has_feature_metadata_csum(fs->super))
                csum_size = sizeof(struct ext2_dir_entry_tail);
 
+       if (buflen < 8) {
+               ctx->errcode = EXT2_ET_DIR_CORRUPTED;
+               return BLOCK_ABORT;
+       }
        while (offset < buflen - 8) {
                dirent = (struct ext2_dir_entry *) (ctx->buf + offset);
                if (ext2fs_get_rec_len(fs, dirent, &rec_len))