[Qemu-devel] [PULL 4/5] usb-mtp: use O_NOFOLLOW and O_CLOEXEC.

[Gerd Hoffmann]

Open files and directories with O_NOFOLLOW to avoid symlinks attacks.
While being at it also add O_CLOEXEC.

usb-mtp only handles regular files and directories and ignores
everything else, so users should not see a difference.

Because qemu ignores symlinks, carrying out a successful symlink attack
requires swapping an existing file or directory below rootdir for a
symlink and winning the race against the inotify notification to qemu.

Fixes: CVE-2018-16872
Cc: Prasad J Pandit <address@hidden>
Cc: Bandan Das <address@hidden>
Reported-by: Michael Hanselmann <address@hidden>
Signed-off-by: Gerd Hoffmann <address@hidden>
Reviewed-by: Michael Hanselmann <address@hidden>
Message-id: address@hidden
---
 hw/usb/dev-mtp.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/hw/usb/dev-mtp.c b/hw/usb/dev-mtp.c
index 100b7171f4..36c43b8c20 100644
--- a/hw/usb/dev-mtp.c
+++ b/hw/usb/dev-mtp.c
@@ -653,13 +653,18 @@ static void usb_mtp_object_readdir(MTPState *s, MTPObject 
*o)
 {
     struct dirent *entry;
     DIR *dir;
+    int fd;
 
     if (o->have_children) {
         return;
     }
     o->have_children = true;
 
-    dir = opendir(o->path);
+    fd = open(o->path, O_DIRECTORY | O_CLOEXEC | O_NOFOLLOW);
+    if (fd < 0) {
+        return;
+    }
+    dir = fdopendir(fd);
     if (!dir) {
         return;
     }
@@ -1007,7 +1012,7 @@ static MTPData *usb_mtp_get_object(MTPState *s, 
MTPControl *c,
 
     trace_usb_mtp_op_get_object(s->dev.addr, o->handle, o->path);
 
-    d->fd = open(o->path, O_RDONLY);
+    d->fd = open(o->path, O_RDONLY | O_CLOEXEC | O_NOFOLLOW);
     if (d->fd == -1) {
         usb_mtp_data_free(d);
         return NULL;
@@ -1031,7 +1036,7 @@ static MTPData *usb_mtp_get_partial_object(MTPState *s, 
MTPControl *c,
                                         c->argv[1], c->argv[2]);
 
     d = usb_mtp_data_alloc(c);
-    d->fd = open(o->path, O_RDONLY);
+    d->fd = open(o->path, O_RDONLY | O_CLOEXEC | O_NOFOLLOW);
     if (d->fd == -1) {
         usb_mtp_data_free(d);
         return NULL;
@@ -1658,7 +1663,7 @@ static void usb_mtp_write_data(MTPState *s)
                                  0, 0, 0, 0);
             goto done;
         }
-        d->fd = open(path, O_CREAT | O_WRONLY, mask);
+        d->fd = open(path, O_CREAT | O_WRONLY | O_CLOEXEC | O_NOFOLLOW, mask);
         if (d->fd == -1) {
             usb_mtp_queue_result(s, RES_STORE_FULL, d->trans,
                                  0, 0, 0, 0);
-- 
2.9.3