lib/posix-sysinfo: Fix off-by-1 error in sethostname

[andreittr]

Description of changes

This change corrects an an off-by-1 error in sethostname when checking the length of the new hostname, leading to a missing terminating NUL byte in the nodename field of struct utsname, contrary to the expected Linux ABI. The suboptimal strncpy call is also replaced with a more appropriate memcpy call, since (1) we know the length of the input string, which (2) does not need to be NUL-terminated.

Additionally, declarations of gethostname and sethostname are added to nolibc's unistd.h, making these functions available to core unikraft as well as microlibraries.

Prerequisite checklist

• Read the contribution guidelines regarding submitting new changes to the project;
• Tested your changes against relevant architectures and platforms;
• Ran the checkpatch.uk on your commit series before opening this PR;
• Updated relevant documentation.

Base target

• Architecture(s): N/A
• Platform(s): N/A
• Application(s): N/A

Additional configuration

CONFIG_LIBPOSIX_SYSINFO=y

Test snippet:

int main(void)
{
	char name[4096];
	int r;

	r = gethostname(name, 4096);
	assert(!r);
	puts(name);

	r = sethostname("123456789012345678901234567890123456789012345678901234567890abcde", 65);
	if (!r) {
		r = gethostname(name, 4096);
		assert(!r);
		puts(name);
	} else {
		puts("Errored out");
	}

	r = sethostname("123456789012345678901234567890123456789012345678901234567890abcde", 64);
	assert(!r);

	r = gethostname(name, 4096);
	assert(!r);
	puts(name);

	return 0;
}

On staging it incorrectly sets a hostname without a NUL byte, resulting in the Unikraft version leaking into the hostname:

SeaBIOS (version 1.16.3-1.fc39)
Booting from ROM..Powered by
o.   .o       _ _               __ _
Oo   Oo  ___ (_) | __ __  __ _ ' _) :_
oO   oO ' _ `| | |/ /  _)' _` | |_|  _)
oOo oOO| | | | |   (| | | (_) |  _) :_
 OoOoO ._, ._:_:_,\_._,  .__,_:_, \___)
               Telesto 0.16.1~4b12ebc89
unikraft
123456789012345678901234567890123456789012345678901234567890abcde5-Telesto
123456789012345678901234567890123456789012345678901234567890abcd

After the fix, it should correctly error out of the first sethostname call:

SeaBIOS (version 1.16.3-1.fc39)
Booting from ROM..Powered by
o.   .o       _ _               __ _
Oo   Oo  ___ (_) | __ __  __ _ ' _) :_
oO   oO ' _ `| | |/ /  _)' _` | |_|  _)
oOo oOO| | | | |   (| | | (_) |  _) :_
 OoOoO ._, ._:_:_,\_._,  .__,_:_, \___)
               Telesto 0.16.1~c704be7ea
unikraft
Errored out
123456789012345678901234567890123456789012345678901234567890abcd

[mariasfiraiala]

Looks good to me, however, please fix the NUL typo in commit's c704be7 message.

[adinamariav]

Aside from what @mariasfiraiala stated here, looks good.

Reviewed-by: Adina-Maria Vaman adinamariav22@gmail.com

[andreittr]

Looks good to me, however, please fix the NUL typo in commit's c704be7 message.

@mariasfiraiala Oh that's on purpose, I meant that as NUL, ASCII abbreviation for char code 0 (aka "the null char", but that "null" is lowercase), instead of NULL, like the null pointer.
I know it's confusing, blame the telecom people behind ascii and their aversion to 4 letter names 😄 .

[mariasfiraiala]

Reviewed-by: Maria Sfiraiala maria.sfiraiala@gmail.com

[razvand]

Approved-by: Razvan Deaconescu razvand@unikraft.io