IB/uverbs: Check reserved field in extended command header

As noted by Daniel Vetter in its article "Botching up ioctls"[1]

  "Check *all* unused fields and flags and all the padding for whether
   it's 0, and reject the ioctl if that's not the case.  Otherwise
   your nice plan for future extensions is going right down the
   gutters since someone *will* submit an ioctl struct with random
   stack garbage in the yet unused parts. Which then bakes in the ABI
   that those fields can never be used for anything else but garbage."

It's important to ensure that reserved fields are set to known value,
so that it will be possible to use them latter to extend the ABI.

The same reasonning apply to comp_mask field present in newer uverbs
command: per commit 22878dbc9173 ("IB/core: Better checking of
userspace values for receive flow steering"), unsupported values in
comp_mask are rejected.

[1] http://blog.ffwll.ch/2013/11/botching-up-ioctls.html

Link: http://marc.info/?i=cover.1386798254.git.ydroneaud@opteya.com>
Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
index 699463bbfd2d569edea591e6eddb83444eee4249..ac2305d8d7c408d0bdf86a208fdda792841e0fb8 100644 (file)
--- a/drivers/infiniband/core/uverbs_main.c
+++ b/drivers/infiniband/core/uverbs_main.c
@@ -668,6 +668,9 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
                if ((hdr.in_words + ex_hdr.provider_in_words) * 8 != count)
                        return -EINVAL;
 
+               if (ex_hdr.cmd_hdr_reserved)
+                       return -EINVAL;
+
                if (ex_hdr.response) {
                        if (!hdr.out_words && !ex_hdr.provider_out_words)
                                return -EINVAL;