Fixed undefined behavior in netmask generation #1717 #1718
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nnposter
reviewed
Aug 31, 2019
| @@ -500,7 +500,7 @@ static int sockaddr_to_mask (const struct sockaddr *sa, int bits, u32 *mask) | |||
| mask[i] = 0; | |||
| } | |||
| else { | |||
| mask[i] = ~((1 << (unmasked_bits - (32 * (4 - i)))) - 1); | |||
| mask[i] = ~(0xffffffff % (1 << unmasked_bits)); | |||
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This code suffers from a similar issue as the original one: There is no guaranteed outcome when unmasked_bits exceeds 31. As an example:
#include <stdio.h>
void main ()
{
int m=32;
printf("%08x\n%08x\n",(0xFFFFFFFF<<(m-1)<<1),(0xFFFFFFFF<<m));
}When compiled with GCC on Ubuntu 18.04 x64:
$ ./a.out
00000000
ffffffff
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I assumed that it would hit another branch if unmasked_bits is a multiple of 32. But I my understanding of how mask is used in the rest of the code is limited, so I might miss something here.
Will test the other patch from the ticket on Monday
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Tested this change on x86_64, i586, ppc, ppc64, ppc64le, aarch64 and s390x. Unit tests passed successfully on these architectures.
Also played around with the test binary (addrset) a bit and could not find any obvious problems with the change.