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List: busybox
Subject: Re: [PATCH v2] echo: do not assume that free() leaves errno unmodified
From: Denys Vlasenko <vda.linux () googlemail ! com>
Date: 2021-02-23 12:01:44
Message-ID: CAK1hOcPD8mVheoOSxUoj07nK8UEMRV3oeJ5h7Wk6NvZSzsCGiw () mail ! gmail ! com
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Applied, thank you.
On Tue, Feb 23, 2021 at 12:31 PM Natanael Copa <ncopa@alpinelinux.org> wrote:
>
> On Fri, 22 Jan 2021 08:35:55 +0100
> Natanael Copa <ncopa@alpinelinux.org> wrote:
>
> > musl libc's mallocng free() may modify errno if kernel does not support
> > MADV_FREE which causes echo to echo with error when it shouldn't.
> >
> > Future versions of POSIX[1] will require that free() leaves errno
> > unmodified but til then, do not rely free() implementation.
> >
> > Should fix downstream issues:
> > https://github.com/alpinelinux/docker-alpine/issues/134
> > https://gitlab.alpinelinux.org/alpine/aports/-/issues/12311
> >
> > Bloatcheck on x86_64:
> >
> > function old new delta
> > echo_main 414 406 -8
> > ------------------------------------------------------------------------------
> > (add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-8) Total: -8
> > bytes
> > text data bss dec hex filename
> > 881114 15196 2000 898310 db506 busybox_old
> > 881106 15196 2000 898302 db4fe busybox_unstripped
> > ---
> >
> > v2: do the free after bb_simple_perror_msg so it prints the correct
> > error message.
> >
> > coreutils/echo.c | 11 +++++------
> > 1 file changed, 5 insertions(+), 6 deletions(-)
> >
> > diff --git a/coreutils/echo.c b/coreutils/echo.c
> > index b3828894c..002832ead 100644
> > --- a/coreutils/echo.c
> > +++ b/coreutils/echo.c
> > @@ -97,6 +97,7 @@ int echo_main(int argc UNUSED_PARAM, char **argv)
> > #else
> > char nflag = 1;
> > char eflag = 0;
> > + int err;
> >
> > while ((arg = *++argv) != NULL) {
> > char n, e;
> > @@ -184,14 +185,12 @@ int echo_main(int argc UNUSED_PARAM, char **argv)
> >
> > do_write:
> > /* Careful to error out on partial writes too (think ENOSPC!) */
> > - errno = 0;
> > - /*r =*/ full_write(STDOUT_FILENO, buffer, out - buffer);
> > - free(buffer);
> > - if (/*WRONG:r < 0*/ errno) {
> > + err = full_write(STDOUT_FILENO, buffer, out - buffer) != out - buffer;
> > + if (err) {
> > bb_simple_perror_msg(bb_msg_write_error);
> > - return 1;
> > }
> > - return 0;
> > + free(buffer);
> > + return err;
> > }
> >
> > /*
>
> Ping. Any change to get this merged?
>
> It fixes a real bug and saves a few bytes.
>
> -nc
> _______________________________________________
> busybox mailing list
> busybox@busybox.net
> http://lists.busybox.net/mailman/listinfo/busybox
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