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Re: [PATCH] QUIC: better sockaddr initialization

Maxim Dounin
May 21, 2023 09:12AM
Hello!

On Sun, May 21, 2023 at 11:31:32AM +0200, Alejandro Colomar wrote:

> On 5/21/23 03:42, Maxim Dounin wrote:
> > # HG changeset patch
> > # User Maxim Dounin <mdounin@mdounin.ru>
> > # Date 1684633125 -10800
> > # Sun May 21 04:38:45 2023 +0300
> > # Node ID 68fa4b86ed46138dd1a8fcf2cfd80206de068bec
> > # Parent 235d482ef6bc8c40a956b2413865d42c94e0fc05
> > QUIC: better sockaddr initialization.
> >
> > The qsock->sockaddr field is a ngx_sockaddr_t union, and therefore can hold
> > any sockaddr (and union members, such qsock->sockaddr.sockaddr, can be used
> > to access appropriate variant of the sockaddr). It is better to set it via
> > qsock->sockaddr itself though, and not qsock->sockaddr.sockaddr, so static
> > analyzers won't complain about out-of-bounds access.
>
> Correct. The previous code was UB, due to memcpy(3) writing to the
> 'struct sockaddr' member. By writing to sockaddr, you were only
> allowed to alias via other members the sa_family_t field, but no
> others.

Well, not really. There is no UB in the previous code, it simply
uses a valid (void *) address to fill the sockaddr (and does so
without breaking strict aliasing rules).

But the code might confuse static analyzers, since they have no
way to know that the whole ngx_sockaddr_t is being set, and not
just the (struct sockaddr) union member which is referenced.

--
Maxim Dounin
http://mdounin.ru/
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Subject Author Views Posted

[PATCH] QUIC: better sockaddr initialization

Maxim Dounin 261 May 20, 2023 09:44PM

Re: [PATCH] QUIC: better sockaddr initialization

Roman Arutyunyan 74 May 21, 2023 05:08AM

Re: [PATCH] QUIC: better sockaddr initialization

Maxim Dounin 73 May 21, 2023 08:58AM

Re: [PATCH] QUIC: better sockaddr initialization

Alejandro Colomar 91 May 21, 2023 05:32AM

Re: [PATCH] QUIC: better sockaddr initialization

Maxim Dounin 80 May 21, 2023 09:12AM

Re: [PATCH] QUIC: better sockaddr initialization

Alejandro Colomar 71 May 21, 2023 10:36AM

Re: [PATCH] QUIC: better sockaddr initialization

Maxim Dounin 81 May 21, 2023 05:24PM

Re: [PATCH] QUIC: better sockaddr initialization

Alejandro Colomar 107 May 21, 2023 07:08PM

Re: [PATCH] QUIC: better sockaddr initialization

Maxim Dounin 78 May 21, 2023 10:36PM

memcpy(3), strict aliasing, pointer provenance rules (was: [PATCH] QUIC: better sockaddr initialization)

Alejandro Colomar 109 May 22, 2023 10:26AM

Re: memcpy(3), strict aliasing, pointer provenance rules (was: [PATCH] QUIC: better sockaddr initialization)

Maxim Dounin 121 May 22, 2023 04:06PM



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