On 12/18/20 10:45 PM, Shi Lei wrote:
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@xxxxxxxxxxxxxx>
---
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.
I tried something a bit different:
https://www.redhat.com/archives/libvir-list/2021-January/msg00311.html
