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Fix alignment issue of ones_complement_checksum

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The ones_complement_checksum function assumes that the bytes passed into
it are aligned on 16 bit boundaries.

When using gcc (GCC) 6.2.1 20160916 (Red Hat 6.2.1-2) with -O2, this
does not seem to hold true anymore; assuming 16 bit alignment will lead
to accesses to uninitialized memory and wrong checksums.

This commit adds a minimally invasive change that does not assume
alignment anymore. This might have a small performance impact for every
single packet we process.

This error occured reproducibly when called from icmp6_checksum.
This commit is contained in:
Johanna Amann 2016-10-14 15:33:43 -07:00
parent bd0a374c87
commit 24f74cb52e
1 changed files with 5 additions and 2 deletions
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7
src/net_util.cc
View file

@ -18,13 +18,16 @@
// Returns the ones-complement checksum of a chunk of b short-aligned bytes. // Returns the ones-complement checksum of a chunk of b short-aligned bytes.
int ones_complement_checksum(const void* p, int b, uint32 sum) int ones_complement_checksum(const void* p, int b, uint32 sum)
{ {
const u_short* sp = (u_short*) p; // better be aligned! const unsigned char* sp = (unsigned char*) p;
b /= 2; // convert to count of short's b /= 2; // convert to count of short's
/* No need for endian conversions. */ /* No need for endian conversions. */
while ( --b >= 0 ) while ( --b >= 0 )
sum += *sp++; {
sum += *sp + ( *(sp+1) << 8 );
sp += 2;
}
while ( sum > 0xffff ) while ( sum > 0xffff )
sum = (sum & 0xffff) + (sum >> 16); sum = (sum & 0xffff) + (sum >> 16);