From: john at keeping.me.uk (John Keeping)
Subject: [PATCH 1/2] gcc8.1: fix strncpy bounds warnings
Date: Sat, 16 Jun 2018 15:14:24 +0100 [thread overview]
Message-ID: <20180616141424.GR1922@john.keeping.me.uk> (raw)
In-Reply-To: <14FAB8D8-6EAD-4EB1-B574-92FC5C6808CC@warmcat.com>
On Sat, Jun 16, 2018 at 09:12:08PM +0800, Andy Green wrote:
>
>
> On June 16, 2018 9:04:48 PM GMT+08:00, John Keeping <john at keeping.me.uk> wrote:
> >On Wed, Jun 13, 2018 at 07:33:59AM +0800, Andy Green wrote:
> >> These warnings are coming on default Fedora 28 build and probably
> >others using gcc 8.1
> >>
> >> ../shared.c: In function ?expand_macro?:
> >> ../shared.c:483:3: warning: ?strncpy? specified bound depends on the
> >length of the source argument [-Wstringop-overflow=]
> >> strncpy(name, value, len);
> >> ^~~~~~~~~~~~~~~~~~~~~~~~~
> >> ../shared.c:480:9: note: length computed here
> >> len = strlen(value);
> >> ^~~~~~~~~~~~~
> >>
> >> strncpy with a computed length via strlen is usually
> >> not the right thing.
> >>
> >> ../ui-shared.c: In function ?cgit_repobasename?:
> >> ../ui-shared.c:135:2: warning: ?strncpy? specified bound 1024 equals
> >destination size [-Wstringop-truncation]
> >> strncpy(rvbuf, reponame, sizeof(rvbuf));
> >> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >>
> >> add one char of padding and adjust so the code does the same.
> >>
> >> Signed-off-by: Andy Green <andy at warmcat.com>
> >> ---
> >> shared.c | 2 +-
> >> ui-shared.c | 7 ++++---
> >> 2 files changed, 5 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/shared.c b/shared.c
> >> index 21ac8f4..477db0a 100644
> >> --- a/shared.c
> >> +++ b/shared.c
> >> @@ -480,7 +480,7 @@ static char *expand_macro(char *name, int
> >maxlength)
> >> len = strlen(value);
> >> if (len > maxlength)
> >> len = maxlength;
> >> - strncpy(name, value, len);
> >> + memcpy(name, value, len);
> >
> >This is a change in behaviour because strncpy is guaranteed to null
> >terminate the output (even writing one beyond len if necessary) whereas
> >memcpy does not.
>
> Eh... are you sure about that? It's not my understanding, and --->
>
> https://linux.die.net/man/3/strncpy
>
> The strncpy() function is similar, except that at most n bytes of src
> are copied. Warning: If there is no null byte among the first n bytes
> of src, the string placed in dest will not be null-terminated.
Yes, I'm getting it confused with strncat. And in this case we do
ensure that the output is null terminated separately.
next prev parent reply other threads:[~2018-06-16 14:14 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-12 23:33 andy
2018-06-12 23:34 ` [PATCH 2/2] gcc8.1: fix strcat warning andy
2018-06-16 13:11 ` john
2018-06-16 21:52 ` list
2018-06-17 2:28 ` andy
2018-06-16 13:04 ` [PATCH 1/2] gcc8.1: fix strncpy bounds warnings john
2018-06-16 13:07 ` [PATCH 1/2] shared: allocate return value from expand_macros() john
2018-06-16 13:07 ` [PATCH 2/2] shared: use strbuf for expanding macros john
2018-06-16 13:12 ` [PATCH 1/2] gcc8.1: fix strncpy bounds warnings andy
2018-06-16 14:14 ` john [this message]
2018-06-26 11:36 ` [PATCH v2 0/2] " andy
2018-06-26 11:36 ` [PATCH v2 1/2] " andy
2018-06-26 11:36 ` [PATCH v2 2/2] cgit_repobasename: convert to allocated result andy
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