Re: [RFC net-next] ppp: remove BSD-Compress support

[sashiko-bot@kernel.org]

> The BSD-Compress decoder assumes that accm is 32 bits, but declares it
> as unsigned long. On 64-bit systems, consumed code bits survive the
> left shift and corrupt the next code. An x86-64 PPP-over-PTY loopback
> test reproduces a fatal bad-code error on the first compressed packet.
> 
> pppd normally requests Deflate in preference to BSD-Compress when both
> methods can be negotiated. If BSD-Compress is selected and encounters
> this fatal error, pppd disables compression and logs:
> 
>   Lost compression sync: disabling compression
> 
> The link remains up and traffic can continue uncompressed.
> 
> The core compression routine has remained unchanged since Linux 2.1.67
> (1997), and the decompression routine since its introduction in Linux
> [ ... ]
> 
> OpenAI Codex assisted with the commit message, cleanup, and PTY testing.
> 
> Link: https://lore.kernel.org/netdev/20240812084312.14127-1-r.smirnov@omp.ru/
> Signed-off-by: Qingfang Deng <qingfang.deng@linux.dev>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261028063452.25812-1-qingfang.deng@linux.dev?part=1