On 12/18/20 10:45 PM, Shi Lei wrote:
On 2020-12-18 at 22:01, John Ferlan wrote:
In virLXCProcessSetupInterfaceTap, containerVeth needs to be freed on failure. Signed-off-by: Shi Lei <shi_lei@massclouds.com> --- src/lxc/lxc_process.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/src/lxc/lxc_process.c b/src/lxc/lxc_process.c index 85d0287a..0f7c9295 100644 --- a/src/lxc/lxc_process.c +++ b/src/lxc/lxc_process.c @@ -303,7 +303,7 @@ virLXCProcessSetupInterfaceTap(virDomainDefPtr vm, const char *brname) { char *parentVeth; Coverity complains that @parentVeth is leaked too - although it's far more opaque and ornery. Let's assume on input that net->ifname != NULL - that means that in virNetDevVethCreate the call to virNetDevGenerateName and the memory in @**ifname (e.g. @parentVeth's copy of net->ifname) will be g_free()'d when !virNetDevExists(try) succeeds and @*ifname gets the memory from @try. In this case @try is a g_strdup_printf of @*ifname. So this code essentially free's memory pointed to by net->ifname, but since @parentVeth is used in the call net->ifname is *NOT* updated which is a second problem that Coverity did not note. Then let's say the call to virNetDevGenerateName fails for @veth2... Since on input @orig1 != NULL (e.g. @parentVeth != NULL), we will not VIR_FREE(*veth1); - that's fine given the original assumption, but when we return to virLXCProcessSetupInterfaceTap that means net->ifname will
Coverity reminds us of the ancient software engineering proverb related to being stuck with ownership because you touched the code last :-) - I know this patch didn't cause the problem, but because the code was touched Coverity decided to look harder and found another leak. On 12/16/20 1:01 AM, Shi Lei wrote: point at memory that was g_free'd and @parentVeth will not be free'd, thus Coverity squawks loud and proud about the resource leak - although it doesn't complain about the fact that net->ifname now points to memory that was free'd. As an aside, I see no way on input @*veth2 could not be NULL so in the cleanup path the check for @orig2 would seem to be dead code. Although, sure future changes could alter that reality. As a test if I replace all @parentVeth refs w/ net->ifname - then Coverity is happy again. I will leave it up to Laine or Shi Lei to generate the "real fix" and/or validate that my reading of the logic is right or not ;-). John Thanks! :-)
As far as I can see, if the original net->ifname != NULL, it should be a user-provided name and NOT a template (prefix+'%d'). When @parentVeth (as the copy of net->ifname) is passed into virNetDevGenerateName, this function will leave it unchanged because it is not a template.
So for now these problems will not happen. But for future, I think it's necessary to fix virLXCProcessSetupInterfaceTap.
I agree that it's a right way to replace all *parentVeth* with net->ifname in virLXCProcessSetupInterfaceTap. And the *parentVeth* should be removed.
I tried something a bit different: https://www.redhat.com/archives/libvir-list/2021-January/msg00311.html