Date: Fri, 16 Dec 2005 11:14:12 -0500 From: John Baldwin <jhb@freebsd.org> To: freebsd-hackers@freebsd.org Cc: Peter Jeremy <PeterJeremy@optushome.com.au>, "Wojciech A. Koszek" <dunstan@freebsd.czest.pl>, phk@freebsd.org Subject: Re: [CALL FOR TESTERS] New system call: abort2() Message-ID: <200512161114.14398.jhb@freebsd.org> In-Reply-To: <20051216091057.GQ77268@cirb503493.alcatel.com.au> References: <20051215223745.GA37768@FreeBSD.czest.pl> <20051216091057.GQ77268@cirb503493.alcatel.com.au>
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On Friday 16 December 2005 04:10 am, Peter Jeremy wrote:
> On Thu, 2005-Dec-15 22:37:45 +0000, Wojciech A. Koszek wrote:
> > abort2(const char *why, int nargs, void **args);
> >
> >"why" is reason of program abort, "nargs" is number of arguments
> >passed in "args". Both "why" and "args" (with "%p" format) will be
> >printed via log(9). Sample output:
> >[..]
> >pid <3004> <abort2> abort2: ABORT2 <arg0:0x62612f2e>
> >pid <3019> <abort2> abort2: invalid argument
> >[..]
>
> I don't believe the following code is correct. uap->args is a
> userspace pointer so uap->args[i] is dereferencing a userspace
> argument in kernelspace.
> + arg = uargs[i] = (void *) fuword(uap->args[i]);
> I think it should be fuword(uap->args + i);
>
> I don't see the point of the following test. "arg" is printed using
> %p and never de-referenced so there's no reason it can't be NULL. I
> would see that a legitimate use of abort2() is when the application
> detects that a pointer is unexpectedly NULL. Aborting on -1 is less
> clear - if fuword() fails, it will return -1 but, equally, a faulty
> user application may have left -1 in a pointer. (Note that mmap(2)
> returns -1 on error so it's not inconceivable that a pointer could
> contain -1).
>
> + /* Prevent from faults in user-space */
> + if (arg == NULL || arg == (void *)-1) {
> + error = EINVAL;
> + break;
> + }
>
> Taking the above into account, I believe the code should be:
> + if (uap->args == NULL)
> + break;
> + error = copyin(uap->args, uargs, uap->nargs * sizeof (void
> *)); + if (error != 0)
> + break;
Agreed. Also, copyinstr() can provide a better interface for copying the why
string in. Also, the PROC LOCK isn't needed for reading the static p_pid and
p_comm fields of struct proc. Also, I second the other comments of do { }
while(0) vs goto. Many existing syscalls use 'goto out;' for error handling,
and I think that is one of the very few cases when goto is useful and not
harmful.
--
John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve" = http://www.FreeBSD.org
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