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

Overview

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.

Affected

• Linux >= 9aaaa56845a06aeabdd597cbe19492dc01f281ec < 49a5faaa471ddcd37b6893970c9916eb836e7c31
• Linux >= 9aaaa56845a06aeabdd597cbe19492dc01f281ec < 91359966e247c0244c66d50bbb8e74aefa4321c3
• Linux >= 9aaaa56845a06aeabdd597cbe19492dc01f281ec < 410351158dfef2d67fea6603680b3a6013c6ed9d
• Linux >= 9aaaa56845a06aeabdd597cbe19492dc01f281ec < acdc12b71c9aa4be5dcd2c8062753c6d2033e235
• Linux >= 9aaaa56845a06aeabdd597cbe19492dc01f281ec < 929b1548e63ac72e104c07d8ee8cbbeeba2fa89a
• Linux >= 9aaaa56845a06aeabdd597cbe19492dc01f281ec < af855f4c966afafef74faf8390c7b86568c0d46d
• Linux >= 9aaaa56845a06aeabdd597cbe19492dc01f281ec < b9c015ef1a7bf1e8dc67f21c6381f36deb2c3a36
• Linux >= 9aaaa56845a06aeabdd597cbe19492dc01f281ec < ff26a0e8377dec07e4a7230db7675bed1b9a6d03
• Linux d529d6c9f7e3aaeac13c4948f79799ccb825f29d
• Linux >= 5.4.14 < 5.5
• Linux 5.5

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.