[Qemu-devel] [PATCH 5/7] 9pfs: don't create files if pathname already exists

[Greg Kurz]

As specified in the http://man.cat-v.org/plan_9/5/open :

"An attempt to create a file in a directory where the given
name already exists will be rejected"

Malicious code in a guest could for example create a named pipe and
then pass its name to the server in a RLCREATE message. This would
cause QEMU to hang in open(), waiting for someone to open the other
end of the pipe.

Let's fix this by simply using O_EXCL.

Signed-off-by: Greg Kurz <gr...@kaod.org>
---
 hw/9pfs/9p.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index edd7b97270e3..d9686601deda 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -1545,7 +1545,7 @@ static void coroutine_fn v9fs_lcreate(void *opaque)
 
     flags = get_dotl_openflags(pdu->s, flags);
     err = v9fs_co_open2(pdu, fidp, &name, gid,
-                        flags | O_CREAT, mode, &stbuf);
+                        flags | O_CREAT | O_EXCL, mode, &stbuf);
     if (err < 0) {
         goto out;
     }
@@ -2252,7 +2252,8 @@ static void coroutine_fn v9fs_create(void *opaque)
         v9fs_path_copy(&fidp->path, &path);
     } else {
         err = v9fs_co_open2(pdu, fidp, &name, -1,
-                            omode_to_uflags(mode)|O_CREAT, perm, &stbuf);
+                            omode_to_uflags(mode) | O_CREAT | O_EXCL, perm,
+                            &stbuf);
         if (err < 0) {
             goto out;
         }