fuse: listxattr: verify xattr list

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@redhat.com>
Cc: <stable@vger.kernel.org>

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index c47b7780ce37bfdf85c35ebc5ef6bf390f9c70e7..b87c9bcd6306c0bc9bb68df8e0f0fb746bcfd0ca 100644 (file)
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1801,6 +1801,23 @@ static ssize_t fuse_getxattr(struct dentry *entry, struct inode *inode,
        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 dentry *entry, char *list, size_t size)
        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;