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From: Christoph Hellwig <hch@lst.de>
To: Joel Becker <jlbec@evilplan.org>
Cc: Sishuai Gong <sishuai@purdue.edu>,
	Al Viro <viro@zeniv.linux.org.uk>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: [PATCH 4/4] configfs: fix a race in configfs_lookup()
Date: Wed, 25 Aug 2021 08:49:06 +0200	[thread overview]
Message-ID: <20210825064906.1694233-5-hch@lst.de> (raw)
In-Reply-To: <20210825064906.1694233-1-hch@lst.de>

From: Sishuai Gong <sishuai@purdue.edu>

When configfs_lookup() is executing list_for_each_entry(),
it is possible that configfs_dir_lseek() is calling list_del().
Some unfortunate interleavings of them can cause a kernel NULL
pointer dereference error

Thread 1                  Thread 2
//configfs_dir_lseek()    //configfs_lookup()
list_del(&cursor->s_sibling);
                         list_for_each_entry(sd, ...)

Fix this by grabbing configfs_dirent_lock in configfs_lookup()
while iterating ->s_children.

Signed-off-by: Sishuai Gong <sishuai@purdue.edu>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/configfs/dir.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index fc20bd8a6337..1466b5d01cbb 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -439,13 +439,13 @@ static struct dentry * configfs_lookup(struct inode *dir,
 	if (!configfs_dirent_is_ready(parent_sd))
 		return ERR_PTR(-ENOENT);
 
+	spin_lock(&configfs_dirent_lock);
 	list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {
 		if ((sd->s_type & CONFIGFS_NOT_PINNED) &&
 		    !strcmp(configfs_get_name(sd), dentry->d_name.name)) {
 			struct configfs_attribute *attr = sd->s_element;
 			umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
 
-			spin_lock(&configfs_dirent_lock);
 			dentry->d_fsdata = configfs_get(sd);
 			sd->s_dentry = dentry;
 			spin_unlock(&configfs_dirent_lock);
@@ -462,10 +462,11 @@ static struct dentry * configfs_lookup(struct inode *dir,
 				inode->i_size = PAGE_SIZE;
 				inode->i_fop = &configfs_file_operations;
 			}
-			break;
+			goto done;
 		}
 	}
-
+	spin_unlock(&configfs_dirent_lock);
+done:
 	d_add(dentry, inode);
 	return NULL;
 }
-- 
2.30.2


  parent reply	other threads:[~2021-08-25  6:53 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-25  6:49 configfs lookup race fix Christoph Hellwig
2021-08-25  6:49 ` [PATCH 1/4] configfs: return -ENAMETOOLONG earlier in configfs_lookup Christoph Hellwig
2021-08-31  5:50   ` Joel Becker
2021-08-31  5:52   ` Joel Becker
2021-08-25  6:49 ` [PATCH 2/4] configfs: simplify the configfs_dirent_is_ready Christoph Hellwig
2021-08-31  5:51   ` Joel Becker
2021-08-25  6:49 ` [PATCH 3/4] configfs: fold configfs_attach_attr into configfs_lookup Christoph Hellwig
2021-08-31  5:52   ` Joel Becker
2021-08-25  6:49 ` Christoph Hellwig [this message]
2021-08-31  5:53   ` [PATCH 4/4] configfs: fix a race in configfs_lookup() Joel Becker

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