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From: Bruce Richardson <bruce.richardson@intel.com>
To: David Marchand <david.marchand@redhat.com>
Cc: Kevin Laatz <kevin.laatz@intel.com>, dev <dev@dpdk.org>,
	"Yigit, Ferruh" <ferruh.yigit@intel.com>,
	dpdk stable <stable@dpdk.org>
Subject: Re: [dpdk-stable] [dpdk-dev] [PATCH] net/ring: fix unchecked return value
Date: Wed, 23 Sep 2020 10:39:27 +0100
Message-ID: <20200923093927.GA1757@bricha3-MOBL.ger.corp.intel.com> (raw)
In-Reply-To: <CAJFAV8z-XF2dr0ZAUL6AFsGzGzz5kxpHvRBVxrxZsgZm1PHU7Q@mail.gmail.com>

On Wed, Sep 23, 2020 at 10:06:25AM +0200, David Marchand wrote:
> On Tue, Sep 22, 2020 at 7:25 PM Kevin Laatz <kevin.laatz@intel.com> wrote:
> >
> > Add a check for the return value of the sscanf call in
> > parse_internal_args(), returning an error if we don't get the expected
> > result.
> >
> > Coverity issue: 362049
> > Fixes: 96cb19521147 ("net/ring: use EAL APIs in PMD specific API")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Kevin Laatz <kevin.laatz@intel.com>
> > ---
> >  drivers/net/ring/rte_eth_ring.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/ring/rte_eth_ring.c b/drivers/net/ring/rte_eth_ring.c
> > index 40fe1ca4ba..62060e46ce 100644
> > --- a/drivers/net/ring/rte_eth_ring.c
> > +++ b/drivers/net/ring/rte_eth_ring.c
> > @@ -539,7 +539,8 @@ parse_internal_args(const char *key __rte_unused, const char *value,
> >         struct ring_internal_args **internal_args = data;
> >         void *args;
> >
> > -       sscanf(value, "%p", &args);
> > +       if (sscanf(value, "%p", &args) != 1)
> > +               return -1;
> 
> Not sure this really needs fixing, as I understood the internal option
> is something only the driver uses.
> 
> On the patch itself, sscanf stops at the first character it deems
> incorrect, meaning that you would not detect trailing chars, like for
> 0x1234Z.
> You can detect this by adding a canary.
> 
> $ cat sscanf.c
> #include <stdio.h>
> 
> int main(int argc, char *argv[])
> {
>     void *args;
>     char c;
> 
>     if (sscanf(argv[1], "%p", &args) != 1)
>         printf("'%%p' KO for %s\n", argv[1]);
>     else
>         printf("'%%p' ok for %s\n", argv[1]);
> 
>     if (sscanf(argv[1], "%p%c", &args, &c) != 1)
>         printf("'%%p%%c' KO for %s\n", argv[1]);
>     else
>         printf("'%%p%%c' ok for %s\n", argv[1]);
>     return 0;
> }
> 
> $ gcc -o sscanf -Wall -Werror sscanf.c
> 
> $ ./sscanf 0x1234
> '%p' ok for 0x1234
> '%p%c' ok for 0x1234
> 
> $ ./sscanf 0x1234Z
> '%p' ok for 0x1234Z
> '%p%c' KO for 0x1234Z
> 
I think a more standard way of checking for trailing chars is to use %n
which stores the number of chars processed. Then check that against
strlen.

For example something like:

if (sscanf(value, "%p%n", args, n) != 1 || n != strlen(value)) {
  /* do error handling */
}

  reply index

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-22 17:20 [dpdk-stable] " Kevin Laatz
2020-09-23  8:06 ` [dpdk-stable] [dpdk-dev] " David Marchand
2020-09-23  9:39   ` Bruce Richardson [this message]
2020-09-23  9:43     ` David Marchand
2020-09-23 10:04       ` Kevin Laatz
2020-09-23 10:25       ` Bruce Richardson
2020-09-25 12:43 ` [dpdk-stable] " Ferruh Yigit
2020-10-01 14:14   ` Kevin Laatz
2020-10-01 14:51     ` Ferruh Yigit
2020-10-01 17:09 ` [dpdk-stable] [PATCH v2] " Kevin Laatz
2020-10-12 11:57   ` Ferruh Yigit
2020-10-12 12:45     ` Bruce Richardson
2020-10-12 13:04       ` Ferruh Yigit
2020-10-12 13:11         ` Bruce Richardson
2020-10-13 13:07   ` [dpdk-stable] [PATCH v3] " Kevin Laatz
2020-10-13 17:23     ` Ferruh Yigit

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