linux-kernel - [PATCH v2] fs: minix: Fix handling of corrupted directories

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Message-ID: <20250514103837.27152-1-kitotavrik.s@gmail.com>
Date: Wed, 14 May 2025 13:38:35 +0300
From: Andrey Kriulin <kitotavrik.s@...il.com>
To: Christian Brauner <brauner@...nel.org>
Cc: Andrey Kriulin <kitotavrik.s@...il.com>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Josef Bacik <josef@...icpanda.com>,
	NeilBrown <neilb@...e.de>,
	Jan Kara <jack@...e.cz>,
	linux-kernel@...r.kernel.org,
	lvc-project@...uxtesting.org,
	stable@...r.kernel.org,
	Andrey Kriulin <kitotavrik.media@...il.com>
Subject: [PATCH v2] fs: minix: Fix handling of corrupted directories

If the directory is corrupted and the number of nlinks is less than 2
(valid nlinks have at least 2), then when the directory is deleted, the
minix_rmdir will try to reduce the nlinks(unsigned int) to a negative
value.

Make nlinks validity check for directory.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@...r.kernel.org
Signed-off-by: Andrey Kriulin <kitotavrik.media@...il.com>
Signed-off-by: Andrey Kriulin <kitotavrik.s@...il.com>
---
v2: Move nlinks validaty check to V[12]_minix_iget() per Jan Kara
<jack@...e.cz> request. Change return error code to EUCLEAN. Don't block
directory in r/o mode per Al Viro <viro@...iv.linux.org.uk> request.

 fs/minix/inode.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/fs/minix/inode.c b/fs/minix/inode.c
index f007e389d5d2..d815397b8b0d 100644
--- a/fs/minix/inode.c
+++ b/fs/minix/inode.c
@@ -517,6 +517,14 @@ static struct inode *V1_minix_iget(struct inode *inode)
 		iget_failed(inode);
 		return ERR_PTR(-ESTALE);
 	}
+	if (S_ISDIR(raw_inode->i_mode) && raw_inode->i_nlinks < 2) {
+		printk("MINIX-fs: inode directory with corrupted number of links");
+		if (!sb_rdonly(inode->i_sb)) {
+			brelse(bh);
+			iget_failed(inode);
+			return ERR_PTR(-EUCLEAN);
+		}
+	}
 	inode->i_mode = raw_inode->i_mode;
 	i_uid_write(inode, raw_inode->i_uid);
 	i_gid_write(inode, raw_inode->i_gid);
@@ -555,6 +563,14 @@ static struct inode *V2_minix_iget(struct inode *inode)
 		iget_failed(inode);
 		return ERR_PTR(-ESTALE);
 	}
+	if (S_ISDIR(raw_inode->i_mode) && raw_inode->i_nlinks < 2) {
+		printk("MINIX-fs: inode directory with corrupted number of links");
+		if (!sb_rdonly(inode->i_sb)) {
+			brelse(bh);
+			iget_failed(inode);
+			return ERR_PTR(-EUCLEAN);
+		}
+	}
 	inode->i_mode = raw_inode->i_mode;
 	i_uid_write(inode, raw_inode->i_uid);
 	i_gid_write(inode, raw_inode->i_gid);
-- 
2.47.2