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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        syzbot+a9ac3de1b5de5fb10efc@syzkaller.appspotmail.com,
        syzbot+df958cf5688a96ad3287@syzkaller.appspotmail.com,
        Eric Biggers <ebiggers@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Qiujun Huang <anenbupt@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH 4.19 151/168] fs/minix: dont allow getting deleted inodes
Date:   Mon, 17 Aug 2020 17:18:02 +0200
Message-Id: <20200817143741.211672047@linuxfoundation.org>
In-Reply-To: <20200817143733.692105228@linuxfoundation.org>
References: <20200817143733.692105228@linuxfoundation.org>
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From: Eric Biggers <ebiggers@google.com>

commit facb03dddec04e4aac1bb2139accdceb04deb1f3 upstream.

If an inode has no links, we need to mark it bad rather than allowing it
to be accessed.  This avoids WARNINGs in inc_nlink() and drop_nlink() when
doing directory operations on a fuzzed filesystem.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+a9ac3de1b5de5fb10efc@syzkaller.appspotmail.com
Reported-by: syzbot+df958cf5688a96ad3287@syzkaller.appspotmail.com
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Qiujun Huang <anenbupt@gmail.com>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200628060846.682158-3-ebiggers@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/minix/inode.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

--- a/fs/minix/inode.c
+++ b/fs/minix/inode.c
@@ -471,6 +471,13 @@ static struct inode *V1_minix_iget(struc
 		iget_failed(inode);
 		return ERR_PTR(-EIO);
 	}
+	if (raw_inode->i_nlinks == 0) {
+		printk("MINIX-fs: deleted inode referenced: %lu\n",
+		       inode->i_ino);
+		brelse(bh);
+		iget_failed(inode);
+		return ERR_PTR(-ESTALE);
+	}
 	inode->i_mode = raw_inode->i_mode;
 	i_uid_write(inode, raw_inode->i_uid);
 	i_gid_write(inode, raw_inode->i_gid);
@@ -504,6 +511,13 @@ static struct inode *V2_minix_iget(struc
 		iget_failed(inode);
 		return ERR_PTR(-EIO);
 	}
+	if (raw_inode->i_nlinks == 0) {
+		printk("MINIX-fs: deleted inode referenced: %lu\n",
+		       inode->i_ino);
+		brelse(bh);
+		iget_failed(inode);
+		return ERR_PTR(-ESTALE);
+	}
 	inode->i_mode = raw_inode->i_mode;
 	i_uid_write(inode, raw_inode->i_uid);
 	i_gid_write(inode, raw_inode->i_gid);