Re: [PATCH] src/ext4_resize.c: set errno to 0 before the strtoull call

["H.J. Lu" <hjl.tools@gmail.com>]

On Tue, Jan 18, 2022 at 6:22 AM Andreas Schwab <schwab@linux-m68k.org> wrote:
>
> On Jan 18 2022, xuyang2018.jy@fujitsu.com wrote:
>
> > Now, I use glibc-2.34 and run the following program[1] but the errno is
> > not 0 in the beginning. So is this a known bug on glibc-2.34(Theodore
> > doesn't meet this problem on glicb-2.31)?
> >
> > [1]https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git/tree/src/ext4_resize.c
>
> Note that there is a call to open preceding the strtoull call, so no
> guarantees can be made about the value of errno before the latter.
>

strtoull man page:

RETURN VALUE
       The strtoul() function returns either the result of the conversion  or,
       if  there  was  a leading minus sign, the negation of the result of the
       conversion represented as an unsigned value, unless the original  (non‐
       negated)  value  would  overflow; in the latter case, strtoul() returns
       ULONG_MAX and sets errno to ERANGE.  Precisely the same holds for  str‐
       toull() (with ULLONG_MAX instead of ULONG_MAX).

new_size = strtoull(argv[2], &tmp, 10);
if ((errno) || (*tmp != '\0')) {
^^^^^^^^^^^^ Shouldn't errno be checked only after the prior function
return value is checked first?

fprintf(stderr, "%s: invalid new size\n", argv[0]);
return 1;
}

-- 
H.J.