Date: Mon, 19 Dec 2005 14:24:04 -0500 From: John Baldwin <jhb@freebsd.org> To: "Wojciech A. Koszek" <dunstan@freebsd.czest.pl> Cc: freebsd-hackers@freebsd.org, phk@freebsd.org, Peter Jeremy <PeterJeremy@optushome.com.au> Subject: Re: [CALL FOR TESTERS] New system call: abort2() Message-ID: <200512191424.06516.jhb@freebsd.org> In-Reply-To: <20051216221943.GB58739@FreeBSD.czest.pl> References: <20051215223745.GA37768@FreeBSD.czest.pl> <200512161114.14398.jhb@freebsd.org> <20051216221943.GB58739@FreeBSD.czest.pl>
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On Friday 16 December 2005 05:19 pm, Wojciech A. Koszek wrote: > On Fri, Dec 16, 2005 at 11:14:12AM -0500, John Baldwin wrote: > > 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. > > Thanks for the suggestions and comments! > > My question is related with copying string from user-space: the only > difference I can see between those functions (other than operating of > strings/sbufs) is that sbuf_copyin() looses 'done' [1]. Since current > abort2() makes use of sbuf(9), I'll have to have additional buffer just > for string copying and than copy it to sbuf. Would you prefer this > solution or complete migration from sbufs to strl..()? > > [1] Couldn't sbuf_copyin() simply return 'done' from copyinstr() > embedded in it, since it already returns -1 on failure? This function > is used in two places, which make no use of return value. That sounds good to me (fixing sbuf_copyin()). -- 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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