linux-kernel - [PATCH] udf: Prevent rmdir of deleted directories

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Message-ID: <20241202004104.20604-2-leocstone@gmail.com>
Date: Sun,  1 Dec 2024 16:41:02 -0800
From: Leo Stone <leocstone@...il.com>
To: syzbot+5df2d3fa14f2d3e49305@...kaller.appspotmail.com,
	jack@...e.com
Cc: Leo Stone <leocstone@...il.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] udf: Prevent rmdir of deleted directories

The syzbot reproducer mounts a UDF image with the undelete option
enabled. It then creates a directory, and eventually attempts to call
rmdir on it 65 times. Because the undelete option is set, the
directory still gets found in udf_fiiter_find_entry(), and the link
count of its parent directory is decremented until it triggers the
warning in drop_nlink().

Prevent directories with the FID_FILE_CHAR_DELETED flag set from being
deleted again.

#syz test

Reported-by: syzbot+5df2d3fa14f2d3e49305@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=5df2d3fa14f2d3e49305
Signed-off-by: Leo Stone <leocstone@...il.com>
---
 fs/udf/namei.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/udf/namei.c b/fs/udf/namei.c
index 78a603129dd5..0a577b7459de 100644
--- a/fs/udf/namei.c
+++ b/fs/udf/namei.c
@@ -504,6 +504,12 @@ static int udf_rmdir(struct inode *dir, struct dentry *dentry)
 	if (ret)
 		goto out;
 
+	if (iter.fi.fileCharacteristics & FID_FILE_CHAR_DELETED) {
+		udf_warn(inode->i_sb,
+			 "tried to rmdir a directory that was already deleted\n");
+		ret = -ENOENT;
+		goto end_rmdir;
+	}
 	ret = -EFSCORRUPTED;
 	tloc = lelb_to_cpu(iter.fi.icb.extLocation);
 	if (udf_get_lb_pblock(dir->i_sb, &tloc, 0) != inode->i_ino)
-- 
2.43.0