Fix IP fragmentation checks for big-endian CPUs #2919
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robertc2000
requested changes
Oct 4, 2024
src/net_builtin.c
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| ip->ver = 0x45; // Version 4, header length 5 words | ||
| ip->frag = 0x40; // Don't fragment | ||
| ip->ver = 0x45; // Version 4, header length 5 words | ||
| ip->frag = mg_htons(0x40); // Don't fragment |
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I think it should be mg_htons(0x4000) instead.
We want to set the first byte at the &ip->frag offset.
Thus, on a little endian mg_htons(0x4000) results in 0x0040, which means the first byte will be written with value 0x40.
On a big endian system instead, mg_htons(0x4000) would still be 0x4000, which means the first byte will be written with 0x40.
In both cases, we set the 'don't fragment' bit correctly.
robertc2000
reviewed
Oct 4, 2024
| @@ -784,7 +784,8 @@ static void rx_tcp(struct mg_tcpip_if *ifp, struct pkt *pkt) { | |||
| } | |||
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| static void rx_ip(struct mg_tcpip_if *ifp, struct pkt *pkt) { | |||
| if (pkt->ip->frag & IP_MORE_FRAGS_MSK || pkt->ip->frag & IP_FRAG_OFFSET_MSK) { | |||
| uint16_t frag = mg_ntohs(pkt->ip->frag); | |||
| if (frag & IP_MORE_FRAGS_MSK || frag & IP_FRAG_OFFSET_MSK) { | |||
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The masks should also be in big endian order.
#define IP_FRAG_OFFSET_MSK 0x1FFF
#define IP_MORE_FRAGS_MSK 0x2000
scaprile
approved these changes
Oct 4, 2024
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