9pfs: local: statfs: don't follow symlinks

The local_statfs() callback is vulnerable to symlink attacks because it
calls statfs() which follows symbolic links in all path elements.

This patch converts local_statfs() to rely on open_nofollow() and fstatfs()
instead.

This partly fixes CVE-2016-9602.

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
(cherry picked from commit 31e51d1c15b35dc98b88a301812914b70a2b55dc)
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index fa1477f6f1575e2a4c71800afe5bab9fbde372c7..80b3964a59fbbcf990eced578cf5febed02c18ea 100644 (file)
--- a/hw/9pfs/9p-local.c
+++ b/hw/9pfs/9p-local.c
@@ -1078,13 +1078,11 @@ static int local_fsync(FsContext *ctx, int fid_type,
 
 static int local_statfs(FsContext *s, V9fsPath *fs_path, struct statfs *stbuf)
 {
-    char *buffer;
-    int ret;
-    char *path = fs_path->data;
+    int fd, ret;
 
-    buffer = rpath(s, path);
-    ret = statfs(buffer, stbuf);
-    g_free(buffer);
+    fd = local_open_nofollow(s, fs_path->data, O_RDONLY, 0);
+    ret = fstatfs(fd, stbuf);
+    close_preserve_errno(fd);
     return ret;
 }