linux-kernel - [PATCH 4.8 20/57] fuse: listxattr: verify xattr list

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Date:   Fri, 21 Oct 2016 11:17:43 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Miklos Szeredi <mszeredi@...hat.com>
Subject: [PATCH 4.8 20/57] fuse: listxattr: verify xattr list

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Miklos Szeredi <mszeredi@...hat.com>

commit cb3ae6d25a5471be62bfe6ac1fccc0e91edeaba0 upstream.

Make sure userspace filesystem is returning a well formed list of xattr
names (zero or more nonzero length, null terminated strings).

[Michael Theall: only verify in the nonzero size case]

Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/fuse/dir.c |   19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1801,6 +1801,23 @@ static ssize_t fuse_getxattr(struct dent
 	return ret;
 }
 
+static int fuse_verify_xattr_list(char *list, size_t size)
+{
+	size_t origsize = size;
+
+	while (size) {
+		size_t thislen = strnlen(list, size);
+
+		if (!thislen || thislen == size)
+			return -EIO;
+
+		size -= thislen + 1;
+		list += thislen + 1;
+	}
+
+	return origsize;
+}
+
 static ssize_t fuse_listxattr(struct dentry *entry, char *list, size_t size)
 {
 	struct inode *inode = d_inode(entry);
@@ -1836,6 +1853,8 @@ static ssize_t fuse_listxattr(struct den
 	ret = fuse_simple_request(fc, &args);
 	if (!ret && !size)
 		ret = outarg.size;
+	if (ret > 0 && size)
+		ret = fuse_verify_xattr_list(list, ret);
 	if (ret == -ENOSYS) {
 		fc->no_listxattr = 1;
 		ret = -EOPNOTSUPP;