netinet: Fix getcred sysctl handlers to do nothing if no input is given

[markj]

Summary

These routines were all assuming that the sysctl handler has some new
value, but this is not the case. SYSCTL_IN() returns 0 in this
scenario, so they were all operating on an uninitialized address. This
is mostly harmless, but trips KMSAN checks, so let's fix them.

[glebius]

IMHO, EINVAL would be better than 0. These are quite non-standard sysctls, that use new value as argument. If actually someone uses them incorrectly, better error than return OK.

[zlei]

Those sysctl handlers copy in a pair of sockaddr_in[6] ( pointed by req->newptr) and copy out the xucred, so what's the point of a NULL req->newptr ? Maybe an error EINVAL is better than 0 ?

Ahh @glebius responses faster than me.

[markj]

It's probably ok to return EINVAL. I was a bit worried that doing so would result in errors from sysctl -a (which is how I found these bugs in the first place), but I think it's ok. Will update.

[zlei]

In D49348#1125484, @markj wrote:

It's probably ok to return EINVAL. I was a bit worried that doing so would result in errors from sysctl -a (which is how I found these bugs in the first place), but I think it's ok. Will update.

No worries. All these sysctl knobs are marked with flag CTLTYPE_OPAQUE, and as per sysctl(8),

-a           List all the currently available values except for those
                  which are opaque or excluded from listing via the
                  CTLFLAG_SKIP flag.  This option is ignored if one or more
                  variable names are specified on the command line.

They should be excluded from sysctl -a.

[markj]

In D49348#1125547, @zlei wrote:

In D49348#1125484, @markj wrote:

It's probably ok to return EINVAL. I was a bit worried that doing so would result in errors from sysctl -a (which is how I found these bugs in the first place), but I think it's ok. Will update.

No worries. All these sysctl knobs are marked with flag CTLTYPE_OPAQUE, and as per sysctl(8),

-a           List all the currently available values except for those
                  which are opaque or excluded from listing via the
                  CTLFLAG_SKIP flag.  This option is ignored if one or more
                  variable names are specified on the command line.

They should be excluded from sysctl -a.

Sure, sysctl -ao then. :)

From reading sysctl.c, I believe no error will be printed in this case, but I still need to check.

[glebius]

btw, do you know which programs use this API?

[markj]

Return EINVAL instead.

[zlei]

Looks good to me.