Re: [PATCHv3 3/3] lxc: fix a memory leak

On 2020-12-18 at 22:01, John Ferlan wrote: > 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: >> In virLXCProcessSetupInterfaceTap, containerVeth needs to be freed on >> failure. >> Signed-off-by: Shi Lei <shi_lei(a)massclouds.com&gt; >> --- >>   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 > 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.