[PATCH 3.16 084/306] fuse: listxattr: verify xattr list

[Ben Hutchings]

3.16.40-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Miklos Szeredi <mszer...@redhat.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 <mszer...@redhat.com>
[bwh: Backported to 3.16: adjust context, indentation]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1968,6 +1968,23 @@ 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 = entry->d_inode;
@@ -2006,9 +2023,11 @@ static ssize_t fuse_listxattr(struct den
        }
        fuse_request_send(fc, req);
        ret = req->out.h.error;
-       if (!ret)
+       if (!ret) {
                ret = size ? req->out.args[0].size : outarg.size;
-       else {
+               if (ret > 0 && size)
+                       ret = fuse_verify_xattr_list(list, ret);
+       } else {
                if (ret == -ENOSYS) {
                        fc->no_listxattr = 1;
                        ret = -EOPNOTSUPP;