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nwfilter: Avoid memory alignment issues

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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@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
This commit is contained in:
Martin Kletzander 2022-03-03 13:18:14 +01:00
parent fad2bff51e
commit 822be8d652
1 changed files with 8 additions and 7 deletions
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15
src/nwfilter/nwfilter_learnipaddr.c
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@ -384,7 +384,7 @@ learnIPAddressThread(void *arg)
struct bpf_program fp; struct bpf_program fp;
struct pcap_pkthdr header; struct pcap_pkthdr header;
const u_char *packet; const u_char *packet;
struct ether_header *ether_hdr; struct ether_header ether_hdr;
struct ether_vlan_header *vlan_hdr; struct ether_vlan_header *vlan_hdr;
virNWFilterIPAddrLearnReq *req = arg; virNWFilterIPAddrLearnReq *req = arg;
uint32_t vmaddr = 0, bcastaddr = 0; uint32_t vmaddr = 0, bcastaddr = 0;
@ -506,13 +506,14 @@ learnIPAddressThread(void *arg)
} }
if (header.len >= sizeof(struct ether_header)) { 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: case ETHERTYPE_IP:
ethHdrSize = sizeof(struct ether_header); ethHdrSize = sizeof(struct ether_header);
etherType = ntohs(ether_hdr->ether_type); etherType = ntohs(ether_hdr.ether_type);
break; break;
case ETHERTYPE_VLAN: case ETHERTYPE_VLAN:
@ -528,7 +529,7 @@ learnIPAddressThread(void *arg)
continue; 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 */ /* packets from the VM */
if (etherType == ETHERTYPE_IP && if (etherType == ETHERTYPE_IP &&
@ -568,9 +569,9 @@ learnIPAddressThread(void *arg)
} }
} }
} else if (virMacAddrCmpRaw(&req->binding->mac, } else if (virMacAddrCmpRaw(&req->binding->mac,
ether_hdr->ether_dhost) == 0 || ether_hdr.ether_dhost) == 0 ||
/* allow Broadcast replies from DHCP server */ /* allow Broadcast replies from DHCP server */
virMacAddrIsBroadcastRaw(ether_hdr->ether_dhost)) { virMacAddrIsBroadcastRaw(ether_hdr.ether_dhost)) {
/* packets to the VM */ /* packets to the VM */
if (etherType == ETHERTYPE_IP && if (etherType == ETHERTYPE_IP &&
(header.len >= ethHdrSize + (header.len >= ethHdrSize +