process/wg: do not check if transport data length is divisible by 16 #200
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added 2 commits
December 16, 2023 13:08
This corrects an implementation flub where I assumed that the length of a WireGuard data packet would always be divisible by 16. That is verifiably false, and the receiving code of WireGuard does not assume that. Padding to the multiples of 16 relates to memory alignment and is mainly a performance measure. It does not always happen; the most common example is traffic approaching the inner MTU, which is set by default to 1420, but can be set to arbitrary values by the user. 1420 is not divisible by 16, and an IP packet of length 1420 is not padded any further by WireGuard. With additional 32 bytes of WireGuard headers and 32 bytes of UDP, IP and frame headers, the total frame length is 1494, which is, again, not divisible by 16. So this check needs to go.
PaulosV
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Codecov ReportAttention:
Additional details and impacted files@@ Coverage Diff @@
## master #200 +/- ##
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+ Coverage 40.90% 40.91% +0.01%
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Files 100 100
Lines 8826 8826
Branches 1312 1312
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+ Hits 3610 3611 +1
+ Misses 4446 4443 -3
- Partials 770 772 +2
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hynekkar
approved these changes
Jan 24, 2024
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This corrects an implementation flub where I assumed that the length of a WireGuard data packet would always be divisible by 16. That is verifiably false, and the receiving code of WireGuard does not assume that.
Zero-padding the message data to the multiples of 16 relates to memory alignment and is mainly a measure to "complicate traffic analysis". It does not always happen; the most common example is traffic approaching the inner MTU, which is set by default to 1420, but can be set to arbitrary values by the user.
1420 is not divisible by 16, and an IP packet of length 1420 is not padded any further by WireGuard. With additional 32 bytes of WireGuard headers and 32 bytes of UDP, IP and frame headers, the total frame length is 1494, which is, again, not divisible by 16.
So this check needs to go.
It may increase the number of false positives, I am going to do some tests about this.