linux-kernel - [PATCH 2/6] fs/minix: don't allow getting deleted inodes

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Date:   Sat, 27 Jun 2020 23:08:41 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     linux-fsdevel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, Qiujun Huang <hqjagain@...il.com>,
        stable@...r.kernel.org,
        syzbot+a9ac3de1b5de5fb10efc@...kaller.appspotmail.com,
        syzbot+df958cf5688a96ad3287@...kaller.appspotmail.com
Subject: [PATCH 2/6] fs/minix: don't allow getting deleted inodes

From: Eric Biggers <ebiggers@...gle.com>

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.

Reported-by: syzbot+a9ac3de1b5de5fb10efc@...kaller.appspotmail.com
Reported-by: syzbot+df958cf5688a96ad3287@...kaller.appspotmail.com
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@...r.kernel.org
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
---
 fs/minix/inode.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/fs/minix/inode.c b/fs/minix/inode.c
index 7cb5fd38eb14..2bca95abe8f4 100644
--- a/fs/minix/inode.c
+++ b/fs/minix/inode.c
@@ -468,6 +468,13 @@ static struct inode *V1_minix_iget(struct inode *inode)
 		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);
@@ -501,6 +508,13 @@ static struct inode *V2_minix_iget(struct inode *inode)
 		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);
-- 
2.27.0