> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of Prof Brian Ripley
> Sent: Friday, November 14, 2008 2:25 AM
> To: Duncan Murdoch
> Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED];
> [EMAIL PROTECTED]
> Subject: Re: [Rd] (PR#13283) R crashes on sprintf with bad
> format specification
>
> As R's sprintf is a wrapper for the OS's sprintf, misuse does
> run the risk of crashing from OS, and when it does the error
> will come from the implementation of sprintf (which for R for
> Windows is the Trio library).
> One could argue that the OS service should not segfault on
> incorrect input, but this one often does.
>
> The place to add checks is in the R wrapper code (presumably
> in the C component). We do have checks there, but it is hard
> to imagine just what errors users will make, and this one has
> slipped through the checks.
The following change recognizes 'S' as a format type (but doesn't
do anything with it) and thus avoids the crash.
--- sprintf.c (revision 46944)
+++ sprintf.c (working copy)
@@ -103,7 +103,7 @@
else {
/* recognise selected types from Table B-1 of K&R */
/* This is MBCS-OK, as we are in a format spec */
- chunk = strcspn(formatString + cur + 1,
"aAdisfeEgGxX%") + 2;
+ chunk = strcspn(formatString + cur + 1,
"aAdisSfeEgGxX%") + 2;
if (cur + chunk > n)
error(_("unrecognised format at end of
string"));
The resulting error messages are not terribly direct, but nicer
than the crash
> sprintf("A %S %S %S XYZ", 1, 1, 1)
Error in sprintf("A %S %S %S XYZ", 1, 1, 1) :
use format %f, %e, %g or %a for numeric objects
> sprintf("A %S %S %S XYZ", "foo", "bar", "foo")
Error in sprintf("A %S %S %S XYZ", "foo", "bar", "foo") :
use format %s for character objects
One could add 'S' to some switch cases below there to have
it convert the corresponding argument to a wide character string
or say directly that %S is not allowed.
This piece of code finds the conversion type by looking for this
first of a bunch of known conversion characters after the %, which
doesn't find lots of illegal formats and causes some surprises. E.g.,
because 'p' is not in that list we get:
> sprintf("%p", 3)
Error in sprintf("%p", 3) : unrecognised format at end of string
> sprintf("%p is a pointer!", 3)
[1] "0x3 is a pointer!"
> sprintf("%p %o", 17L, 17L)
[1] "0x4 o"
> Here the issue is the use of %S, an unknown format for
> numbers, followed by 'X'. There is a check for a suitable
> format, but it is not strict enough. And it is non-trivial
> to write a printf format parser just to check for user error
> (and potentially it will slow down correct uses:
> speed in sprintf is important in some applications).
>
> So I am not sure this is something that should be R's
> responsibility to
> fix: maybe just add a warning to the help page?
>
>
> On Thu, 13 Nov 2008, Duncan Murdoch wrote:
>
> > On 12/11/2008 8:30 PM, [EMAIL PROTECTED] wrote:
> >> Full_Name: Oren Cheyette
> >> Version: 2.7.2
> >> OS: Win XP
> >> Submission from: (NULL) (64.161.123.194)
> >>
> >>
> >> Enter the following at the R command prompt:
> >>> sprintf("A %S %S %S XYZ", 1, 1, 1);
>
> R is not C, and the empty command at the end of that line (after the
> semicolon) is not relevant.
>
> >> Note the erroneous capitalized %S instead of %s and the
> numeric inputs
> >> instead
> >> of strings. With strings there's no crash - R reports bad format
> >> specifications.
> >
> > 2.7.2 is obsolete, but I can confirm a crash on Windows
> with a recent
> > R-devel.
> >
> > The last few entries in the stack dump at the time of the
> crash are shown
> > below; these make it look as though the problem is in the
> Trio library, so it
> > may be hard to fix.
> >
> > Duncan Murdoch
> >
> >
> > Rgui.exe caused an Access Violation at location 6c913fb3 in
> module R.dll
> > Reading from location 00000001.
> >
> > Registers:
> > eax=7fffffff ebx=00000000 ecx=00e17b21 edx=00000001
> esi=00e1c83b edi=0000000a
> > eip=6c913fb3 esp=00e17944 ebp=00e17b3c iopl=0 nv up
> ei pl nz na po nc
> > cs=001b ss=0023 ds=0023 es=0023 fs=003b gs=0000 efl=00000206
> >
> > Call stack:
> > 6C913FB3 R.dll:6C913FB3 TrioFormatProcess trio.c:2724
> >
> > ...
> > while (length > 0)
> > {
> >> size = TrioWriteWideStringCharacter(self,
> *wstring++, flags,
> > length);
> > if (size == 0)
> > break; /* while */
> > ...
> >
> > 6C916592 R.dll:6C916592 trio_vsprintf trio.c:3771
> >
> > ...
> > return status;
> >
> >> status = TrioFormatProcess(&data, format, parameters);
> > if (data.error != 0)
> > {
> > ...
> >
> > 6C911F62 R.dll:6C911F62 sprintf compat.c:46
> >
> > ...
> > va_end(ap);
> > return res;
> >> }
> >
> >
> > ...
> >
> > 6C889F1E R.dll:6C889F1E do_sprintf sprintf.c:297
> >
> > ...
> > sprintf(bit, fmtp, " NaN");
> > else
> >> sprintf(bit, fmtp, "NaN");
> > } else if (x == R_PosInf) {
> > if (strcspn(fmtp, "+") < strlen(fmtp))
> > ...
> >
> > ______________________________________________
> > R-devel@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
> >
>
> --
> Brian D. Ripley, [EMAIL PROTECTED]
> Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
> University of Oxford, Tel: +44 1865 272861 (self)
> 1 South Parks Road, +44 1865 272866 (PA)
> Oxford OX1 3TG, UK Fax: +44 1865 272595
>
> ______________________________________________
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
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