linux-kernel - [PATCH] Fix a drop_nlink warning in minix

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Message-ID: <20251102135239.2203389-1-jkoolstra@xs4all.nl>
Date: Sun,  2 Nov 2025 14:52:39 +0100
From: Jori Koolstra <jkoolstra@...all.nl>
To: Christian Brauner <brauner@...nel.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Taotao Chen <chentaotao@...iglobal.com>,
	Jeff Layton <jlayton@...nel.org>,
	Jan Kara <jack@...e.cz>,
	NeilBrown <neil@...wn.name>
Cc: jkoolstra@...all.nl,
	linux-kernel@...r.kernel.org,
	syzbot+4e49728ec1cbaf3b91d2@...kaller.appspotmail.com
Subject: [PATCH] Fix a drop_nlink warning in minix_rmdir

Syzbot found a drop_nlink warning that is triggered by an easy to
detect nlink corruption of a directory. This patch adds a sanity check
to minix_rmdir to prevent the warning and instead return EFSCORRUPTED to
the caller.

The changes were tested using the syzbot reproducer as well as local
testing.

Signed-off-by: Jori Koolstra <jkoolstra@...all.nl>
Reported-by: syzbot+4e49728ec1cbaf3b91d2@...kaller.appspotmail.com
Closes: https://syzbot.org/bug?extid=4e49728ec1cbaf3b91d2
---
 fs/minix/minix.h |  2 ++
 fs/minix/namei.c | 26 ++++++++++++++++++--------
 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/fs/minix/minix.h b/fs/minix/minix.h
index d54273c3c9ff..ce62cb61186d 100644
--- a/fs/minix/minix.h
+++ b/fs/minix/minix.h
@@ -168,4 +168,6 @@ static inline int minix_test_bit(int nr, const void *vaddr)
 
 #endif
 
+#define EFSCORRUPTED	EUCLEAN		/* Filesystem is corrupted */
+
 #endif /* FS_MINIX_H */
diff --git a/fs/minix/namei.c b/fs/minix/namei.c
index 8938536d8d3c..a8d5a7e22b7b 100644
--- a/fs/minix/namei.c
+++ b/fs/minix/namei.c
@@ -161,15 +161,25 @@ static int minix_unlink(struct inode * dir, struct dentry *dentry)
 static int minix_rmdir(struct inode * dir, struct dentry *dentry)
 {
 	struct inode * inode = d_inode(dentry);
-	int err = -ENOTEMPTY;
-
-	if (minix_empty_dir(inode)) {
-		err = minix_unlink(dir, dentry);
-		if (!err) {
-			inode_dec_link_count(dir);
-			inode_dec_link_count(inode);
-		}
+	int err = -EFSCORRUPTED;
+
+	if (dir->i_nlink <= 2) {
+		printk(KERN_CRIT "minix-fs error: directory inode has "
+		       "corrupted nlink");
+		goto out;
 	}
+
+	err = -ENOTEMPTY;
+	if (!minix_empty_dir(inode))
+		goto out;
+
+	err = minix_unlink(dir, dentry);
+	if (!err) {
+		inode_dec_link_count(dir);
+		inode_dec_link_count(inode);
+ 	}
+
+out:
 	return err;
 }
 
-- 
2.51.1.dirty