From: Adam Borowski <kilobyte@angband.pl>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>,
linux-next <linux-next@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: linux-next: build warnings from Linus' tree
Date: Mon, 20 Aug 2018 03:33:19 +0200 [thread overview]
Message-ID: <20180820013319.slygmbleia55evtl@angband.pl> (raw)
In-Reply-To: <CA+55aFw4WcLcFJkoWoE2v--J3s2Hk8JBU92=Zh351FH7xY8zpw@mail.gmail.com>
On Sun, Aug 19, 2018 at 04:21:57PM -0700, Linus Torvalds wrote:
> On Sun, Aug 19, 2018 at 3:13 PM Stephen Rothwell <sfr@canb.auug.org.au> wrote:
> >
> > Today's linux-next build (powerpc ppc64_defconfig) produced these
> > warnings:
> >
> > fs/cifs/cifssmb.c:605:3: warning: 'strncpy' writing 16 bytes into a region of size 1 overflows the destination [-Wstringop-overflow=]
> > strncpy(pSMB->DialectsArray+count, protocols[i].name, 16);
> >
> > Presumably caused by my update to gcc 8.2.0.
>
> Yeah. There are some patches to mark some arrays as non-strings to get
> rid of these, but we'll see. Maybe we'll just disable the new gcc
> warning if it causes more pain than it is worth.
Every single use of strncpy() for a C string is either a bug, inefficiency,
or both. In this particular case the code:
count = 0;
for (i = 0; i < CIFS_NUM_PROT; i++) {
strncpy(pSMB->DialectsArray+count, protocols[i].name, 16);
count += strlen(protocols[i].name) + 1;
/* null at end of source and target buffers anyway */
}
* pointlessly clears 16 bytes in every iteration
* calculates the string's length twice
* there's no protection against buffer overflow anyway
So what is the strncpy() there for, when an unbounded copy would be just as
good? For other cases, there's a bunch of better functions: strlcpy(),
snprintf(), even strlen()+memcpy(), etc.
Valid uses of strncpy() do exist (such as SCSI structs), but those deal with
fixed-width fields. Thus, gcc is right for warning for at least some of
misuse of strncpy() for C strings. The function wasn't designed for them.
(Skipped analysis why strncpy is always a bad choice for C strings.)
Meow!
--
⢀⣴⠾⠻⢶⣦⠀ What Would Jesus Do, MUD/MMORPG edition:
⣾⠁⢰⠒⠀⣿⡁ • multiplay with an admin char to benefit your mortal [Mt3:16-17]
⢿⡄⠘⠷⠚⠋⠀ • abuse item cloning bugs [Mt14:17-20, Mt15:34-37]
⠈⠳⣄⠀⠀⠀⠀ • use glitches to walk on water [Mt14:25-26]
next prev parent reply other threads:[~2018-08-20 1:33 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-19 22:13 linux-next: build warnings from Linus' tree Stephen Rothwell
2018-08-19 22:16 ` Stephen Rothwell
2018-08-19 22:40 ` Stephen Rothwell
2018-08-19 23:21 ` Linus Torvalds
2018-08-20 1:33 ` Adam Borowski [this message]
2018-08-20 2:53 ` Theodore Y. Ts'o
2018-08-20 0:02 ` Theodore Y. Ts'o
2018-08-20 17:47 ` Miguel Ojeda
-- strict thread matches above, loose matches on Subject: below --
2019-08-29 21:59 Stephen Rothwell
2018-06-11 22:14 Stephen Rothwell
2018-11-14 4:54 ` Joel Stanley
2018-11-14 10:20 ` Michael Ellerman
2018-11-18 11:22 ` Alan Modra
2018-12-03 23:24 ` Joel Stanley
2010-10-28 0:27 Stephen Rothwell
2010-10-28 3:04 ` Mark Brown
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180820013319.slygmbleia55evtl@angband.pl \
--to=kilobyte@angband.pl \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-next@vger.kernel.org \
--cc=sfr@canb.auug.org.au \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).