linux-ext4 - [PATCH 3/7] libext2fs: add check for too-short directory blocks

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Date:   Tue,  7 Jun 2022 00:24:40 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:     Nils Bars <nils.bars@....de>,
        Moritz Schlögel <moritz.schloegel@....de>,
        Nico Schiller <nico.schiller@....de>,
        "Theodore Ts'o" <tytso@....edu>
Subject: [PATCH 3/7] 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@....de>
Reported-by: Moritz Schlögel <moritz.schloegel@....de>
Reported-by: Nico Schiller <nico.schiller@....de>
Signed-off-by: Theodore Ts'o <tytso@....edu>
---
 lib/ext2fs/dir_iterate.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lib/ext2fs/dir_iterate.c b/lib/ext2fs/dir_iterate.c
index b2b77693..7798a482 100644
--- 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))
-- 
2.31.0