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Re: [libvirt] [PATCH 8/8] daemon: Resolve Coverity FORWARD_NULL



On Mon, Sep 15, 2014 at 07:49:09AM -0400, John Ferlan wrote:
On 09/15/2014 04:36 AM, Martin Kletzander wrote:
On Sat, Sep 13, 2014 at 09:27:45AM -0400, John Ferlan wrote:
Coverity complains that the comparison:

 if (nfds && nfds > ((int)!!sock_path + (int)!!sock_path_ro))

could mean 'sock_path' is NULL. Later in virNetSocketNewListenUNIX
there's a direct dereference of path in the error path:

 if (path[0] != '@')

A bit of sleuthing proves that upon entry to daemonSetupNetworking
there is no way for 'sock_path' to be NULL since daemonUnixSocketPaths
will set up 'sock_file' (although it may not set up 'sock_file_ro')
in all 3 paths.

So to keep Coverity quiet - add an sa_assert prior to the call.

Signed-off-by: John Ferlan <jferlan redhat com>
---
daemon/libvirtd.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/daemon/libvirtd.c b/daemon/libvirtd.c
index 05ee50e..028145e 100644
--- a/daemon/libvirtd.c
+++ b/daemon/libvirtd.c
@@ -502,6 +502,7 @@ static int daemonSetupNetworking(virNetServerPtr srv,
            return -1;
    }

+    sa_assert(sock_path);
    if (nfds && nfds > ((int)!!sock_path + (int)!!sock_path_ro)) {

Well, if sock_path cannot be NULL, then why not change it to:

if (nfds > (1 + !!sock_path_ro)) {

or something like that?

Sure, but while I ensured that "today" - who's to say tomorrow someone
doesn't make a change in the future that alters that assumption?  Just
removing "sock_path" still "hides" the fact that someone could
incorrectly pass a NULL sock_path here.  At least the sa_assert() will
cover that.

The "real" reason Coverity complains is because sock_path is eventually
dereferenced elsewhere without first checking if it's NULL, but Coverity
believes this code is check for it being NULL. It's a double edged sword.


Well, then that sa_assert() would make sense being there (where the
dereference happens) or having a check only for that in some
meaningful place.  But I believe we're trying to solve a completely
different problem.  I was just stupid when I wrote the code :)

Another "option" would be to adjust the code in that place to ensure
path is valid before dereferencing.  Of course, knowing that there is
another change pending in this area that I reviewed and that it also
makes the same deref, I think not using sa_assert here would be the gift
that keeps on giving with respect to Coverity complaints.


But having it where you proposed it doesn't really make sense to me
(or is not visible at first).

So, how about the following instead (for equally challenging ternary
operations):

$ git diff
diff --git a/daemon/libvirtd.c b/daemon/libvirtd.c
index 893aacf..5b8f28e 100644
--- a/daemon/libvirtd.c
+++ b/daemon/libvirtd.c
@@ -442,12 +442,13 @@ static void daemonInitialize(void)
}


-static int daemonSetupNetworking(virNetServerPtr srv,
-                                 struct daemonConfig *config,
-                                 const char *sock_path,
-                                 const char *sock_path_ro,
-                                 bool ipsock,
-                                 bool privileged)
+static int ATTRIBUTE_NONNULL(3)
+daemonSetupNetworking(virNetServerPtr srv,
+                      struct daemonConfig *config,
+                      const char *sock_path,
+                      const char *sock_path_ro,
+                      bool ipsock,
+                      bool privileged)
{
    virNetServerServicePtr svc = NULL;
    virNetServerServicePtr svcRO = NULL;
@@ -467,8 +468,7 @@ static int daemonSetupNetworking(virNetServerPtr srv,
            return -1;
    }

-    sa_assert(sock_path);
-    if (nfds && nfds > ((int)!!sock_path + (int)!!sock_path_ro)) {
+    if (nfds && nfds > (sock_path_ro ? 2 : 1)) {
        VIR_ERROR(_("Too many (%u) FDs passed from caller"), nfds);
        return -1;
    }


Yes, and you can remove the "nfds &&" I believe (I have no idea why I
used it there).  ACK with this squashed in.

Martin

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