[libvirt PATCH 4/5] nwfilter: Avoid memory alignment issues

The returned packet can have less strict alignment (u_char) than the struct (ether_header) we are casting it to, so to avoid alignment issues just copy the header into the struct on the stack. Signed-off-by: Martin Kletzander <mkletzan(a)redhat.com&gt; --- src/nwfilter/nwfilter_learnipaddr.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/src/nwfilter/nwfilter_learnipaddr.c b/src/nwfilter/nwfilter_learnipaddr.c index fb552bd1e60e..99bffdc4fbdb 100644 --- a/src/nwfilter/nwfilter_learnipaddr.c +++ b/src/nwfilter/nwfilter_learnipaddr.c @@ -384,7 +384,7 @@ learnIPAddressThread(void *arg) struct bpf_program fp; struct pcap_pkthdr header; const u_char *packet; - struct ether_header *ether_hdr; + struct ether_header ether_hdr; struct ether_vlan_header *vlan_hdr; virNWFilterIPAddrLearnReq *req = arg; uint32_t vmaddr = 0, bcastaddr = 0; @@ -506,13 +506,14 @@ learnIPAddressThread(void *arg) } if (header.len >= sizeof(struct ether_header)) { - ether_hdr = (struct ether_header*)packet; + /* Avoid alignment issues */ + memcpy(&ether_hdr, packet, sizeof(struct ether_header)); - switch (ntohs(ether_hdr->ether_type)) { + switch (ntohs(ether_hdr.ether_type)) { case ETHERTYPE_IP: ethHdrSize = sizeof(struct ether_header); - etherType = ntohs(ether_hdr->ether_type); + etherType = ntohs(ether_hdr.ether_type); break; case ETHERTYPE_VLAN: @@ -528,7 +529,7 @@ learnIPAddressThread(void *arg) continue; } - if (virMacAddrCmpRaw(&req->binding->mac, ether_hdr->ether_shost) == 0) { + if (virMacAddrCmpRaw(&req->binding->mac, ether_hdr.ether_shost) == 0) { /* packets from the VM */ if (etherType == ETHERTYPE_IP && @@ -568,9 +569,9 @@ learnIPAddressThread(void *arg) } } } else if (virMacAddrCmpRaw(&req->binding->mac, - ether_hdr->ether_dhost) == 0 || + ether_hdr.ether_dhost) == 0 || /* allow Broadcast replies from DHCP server */ - virMacAddrIsBroadcastRaw(ether_hdr->ether_dhost)) { + virMacAddrIsBroadcastRaw(ether_hdr.ether_dhost)) { /* packets to the VM */ if (etherType == ETHERTYPE_IP && (header.len >= ethHdrSize + -- 2.35.1