In the Linux kernel, the following vulnerability has been resolved: net: tls: prevent chain...

In the Linux kernel, the following vulnerability has been resolved:

net: tls: prevent chain-after-chain in plain text SG

Sashiko points out that if end = 0 (start != 0) the current code will create a chain link to content type right after the wrap link:

This would create a chain where the wrap link points directly to another chain link. The scatterlist API sg_next iterator does not recursively resolve consecutive chain links.

meaning this is illegal input to crypto.

The wrapping link is unnecessary if end = 0. end is the entry after the last one used so end = 0 means there's nothing pushed after the wrap:

end start i v v v [ ]...[ ][ d ][ d ][ d ][ d ][rsv for wrap]

Skip the wrapping in this case.

TLS 1.3 can use the "wrapping slot" for it's chaining if end = 0. This avoids the chain-after-chain.

Move the wrap chaining before marking END and chaining off content type, that feels like more logical ordering to me, but should not matter from functional perspective.