[libvirt] [PATCHv2] util: don't overwrite stack when getting ethtool gfeatures

This fixes the crash described here: https://www.redhat.com/archives/libvir-list/2015-August/msg00162.html In short, we were calling ioctl(SIOCETHTOOL) pointing to a too-short object that was a local on the stack, resulting in the memory past the end of the object being overwritten. This was because the struct used by the ETHTOOL_GFEATURES command of SIOCETHTOOL ends with a 0-length array, but we were telling ethtool that it could use 2 elements on the array. The fix is to allocate the necessary memory with VIR_ALLOC_VAR(), including the extra length needed for a 2 element array at the end. --- V2 difference: eliminate all the other cleanups that were in V1, just fix the crash. I had misunderstood that a "failure" of the ioctl shouldn't really be considered a *failure*, and don't have time to tweak around with all the inconsequential stuff right now. src/util/virnetdev.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/src/util/virnetdev.c b/src/util/virnetdev.c index 1e20789..c158ca3 100644 --- a/src/util/virnetdev.c +++ b/src/util/virnetdev.c @@ -3130,7 +3130,7 @@ virNetDevGetFeatures(const char *ifname, size_t i = -1; struct ethtool_value cmd = { 0 }; # if HAVE_DECL_ETHTOOL_GFEATURES - struct ethtool_gfeatures g_cmd = { 0 }; + struct ethtool_gfeatures *g_cmd; # endif struct elem{ const int cmd; @@ -3188,10 +3188,14 @@ virNetDevGetFeatures(const char *ifname, # endif # if HAVE_DECL_ETHTOOL_GFEATURES - g_cmd.cmd = ETHTOOL_GFEATURES; - g_cmd.size = GFEATURES_SIZE; - if (virNetDevGFeatureAvailable(ifname, &g_cmd)) + if (VIR_ALLOC_VAR(g_cmd, + struct ethtool_get_features_block, GFEATURES_SIZE) < 0) + return -1; + g_cmd->cmd = ETHTOOL_GFEATURES; + g_cmd->size = GFEATURES_SIZE; + if (virNetDevGFeatureAvailable(ifname, g_cmd)) ignore_value(virBitmapSetBit(*out, VIR_NET_DEV_FEAT_TXUDPTNL)); + VIR_FREE(g_cmd); # endif if (virNetDevRDMAFeature(ifname, out) < 0) -- 2.1.0