Date: Sat, 2 Dec 2006 17:25:00 +0100 From: Alexander Leidinger <Alexander@Leidinger.net> To: arch@freebsd.org Subject: Changing copyinstr(9) invariants Message-ID: <20061202172500.62b03d9c@Magellan.Leidinger.net>
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Hi,
the copyinstr(9) documentation does not guarantee that in the
ENAMETOOLONG case the result is a completely filled up memory region
which contains a truncated string without termination.
The powerpc version works like this. And while I don't understand i386
ASM, it looks to me the i386 version does the same.
My questions:
- Does the amd64/sparc64/ia64/... version do the same?
- Are there reasons not to document this fact and then make use of
it?
My motivation is in the linux_prctl() function in
src/sys/compat/linux/linux_misc.c:
---snip---
case LINUX_PR_SET_NAME:
max_size = MIN(sizeof(comm), sizeof(p->p_comm));
error = copyinstr((void *)(register_t) args->arg2, comm,
max_size, NULL);
/* Linux silently truncates the name if it is too long.
if (error == ENAMETOOLONG) {
/*
* XXX: copyinstr() isn't documented to populate the
* array completely, so do a copyin() to be on the
* safe side. This should be changed in case
* copyinstr() is changed to guarantee this.
*/
error = copyin((void *)(register_t)args->arg2, comm,
max_size - 1);
comm[max_size - 1] = '\0';
}
if (error)
return (error);
---snip---
By documenting this behavior I could get rid of the copyin() and just
terminate the string.
Bye,
Alexander.
--
'I'll tell you this!' shouted Rincewind. 'I'd rather trust me than history! Oh, shit, did I just say that?'
(Interesting Times)
http://www.Leidinger.net Alexander @ Leidinger.net: PGP ID = B0063FE7
http://www.FreeBSD.org netchild @ FreeBSD.org : PGP ID = 72077137
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