Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Soumya Negi <soumya.negi97@gmail.com>
To:     Anton Altaparmakov <anton@tuxera.com>,
        Shuah Khan <skhan@linuxfoundation.org>
Cc:     Soumya Negi <soumya.negi97@gmail.com>,
        linux-ntfs-dev@lists.sourceforge.net, linux-kernel@vger.kernel.org,
        linux-kernel-mentees@lists.linuxfoundation.org
Subject: [PATCH] ntfs: Ensure $Extend is a directory
Date:   Sun, 24 Jul 2022 06:21:07 -0700
Message-Id: <20220724132107.1163-1-soumya.negi97@gmail.com>
Precedence: bulk

Fixes Syzbot bug: kernel BUG in ntfs_lookup_inode_by_name
https://syzkaller.appspot.com/bug?id=32cf53b48c1846ffc25a185a2e92e170d1a95d71

Check whether $Extend is a directory or not( for NTFS3.0+) while loading
system files. If it isn't(as in the case of this bug where the mft record for
$Extend contains a regular file), load_system_files() returns false.

Reported-by: syzbot+30b7f850c6d98ea461d2@syzkaller.appspotmail.com
Signed-off-by: Soumya Negi <soumya.negi97@gmail.com>
---
 fs/ntfs/super.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/ntfs/super.c b/fs/ntfs/super.c
index 5ae8de09b271..18e2902531f9 100644
--- a/fs/ntfs/super.c
+++ b/fs/ntfs/super.c
@@ -2092,10 +2092,15 @@ static bool load_system_files(ntfs_volume *vol)
 	// TODO: Initialize security.
 	/* Get the extended system files' directory inode. */
 	vol->extend_ino = ntfs_iget(sb, FILE_Extend);
-	if (IS_ERR(vol->extend_ino) || is_bad_inode(vol->extend_ino)) {
+	if (IS_ERR(vol->extend_ino) || is_bad_inode(vol->extend_ino) ||
+	    !S_ISDIR(vol->extend_ino->i_mode)) {
+		static const char *es1 = "$Extend is not a directory";
+		static const char *es2 = "Failed to load $Extend";
+		const char *es = !S_ISDIR(vol->extend_ino->i_mode) ? es1 : es2;
+
 		if (!IS_ERR(vol->extend_ino))
 			iput(vol->extend_ino);
-		ntfs_error(sb, "Failed to load $Extend.");
+		ntfs_error(sb, "%s.", es);
 		goto iput_sec_err_out;
 	}
 #ifdef NTFS_RW
-- 
2.17.1