[PATCH] i2c: strncpy does not null terminate string

[PATCH] i2c: strncpy does not null terminate string

[Roel Kluin]

With `sizeof(string) - 1` strncpy() will null terminate the string.

Signed-off-by: Roel Kluin <roel.kluin-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
To test this:

#include <stdio.h>
#include <string.h>

char a[10];
char b[10];

int main()
{
        const char* str = "0123456789012";
        strncpy(a, str, sizeof(a));
        strncpy(b, str, sizeof(b) - 1);
        printf("String a was %s, b was %s\n", a, b);

        return 0;
}

diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
index fdd8327..bede75d 100644
--- a/drivers/i2c/busses/i2c-omap.c
+++ b/drivers/i2c/busses/i2c-omap.c
@@ -879,7 +879,7 @@ omap_i2c_probe(struct platform_device *pdev)
 	i2c_set_adapdata(adap, dev);
 	adap->owner = THIS_MODULE;
 	adap->class = I2C_CLASS_HWMON;
-	strncpy(adap->name, "OMAP I2C adapter", sizeof(adap->name));
+	strncpy(adap->name, "OMAP I2C adapter", sizeof(adap->name) - 1);
 	adap->algo = &omap_i2c_algo;
 	adap->dev.parent = &pdev->dev;
 

Re: [PATCH] i2c: strncpy does not null terminate string

[Jean Delvare]

On Fri, 17 Jul 2009 15:03:24 +0200, Roel Kluin wrote:
> With `sizeof(string) - 1` strncpy() will null terminate the string.
> 
> Signed-off-by: Roel Kluin <roel.kluin-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> ---
> To test this:
> 
> #include <stdio.h>
> #include <string.h>
> 
> char a[10];
> char b[10];
> 
> int main()
> {
>         const char* str = "0123456789012";
>         strncpy(a, str, sizeof(a));
>         strncpy(b, str, sizeof(b) - 1);
>         printf("String a was %s, b was %s\n", a, b);
> 
>         return 0;
> }
> 
> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> index fdd8327..bede75d 100644
> --- a/drivers/i2c/busses/i2c-omap.c
> +++ b/drivers/i2c/busses/i2c-omap.c
> @@ -879,7 +879,7 @@ omap_i2c_probe(struct platform_device *pdev)
>  	i2c_set_adapdata(adap, dev);
>  	adap->owner = THIS_MODULE;
>  	adap->class = I2C_CLASS_HWMON;
> -	strncpy(adap->name, "OMAP I2C adapter", sizeof(adap->name));
> +	strncpy(adap->name, "OMAP I2C adapter", sizeof(adap->name) - 1);
>  	adap->algo = &omap_i2c_algo;
>  	adap->dev.parent = &pdev->dev;

Nack, please just use strlcpy() instead.

IMHO strncpy() should be banned from the kernel.

-- 
Jean Delvare

Re: [PATCH] i2c: strncpy does not null terminate string

[Jean Delvare]

Oh, BTW...

On Fri, 17 Jul 2009 15:06:24 +0200, Jean Delvare wrote:
> On Fri, 17 Jul 2009 15:03:24 +0200, Roel Kluin wrote:
> > With `sizeof(string) - 1` strncpy() will null terminate the string.
> > 
> > Signed-off-by: Roel Kluin <roel.kluin-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> > ---
> > To test this:
> > 
> > #include <stdio.h>
> > #include <string.h>
> > 
> > char a[10];
> > char b[10];
> > 
> > int main()
> > {
> >         const char* str = "0123456789012";
> >         strncpy(a, str, sizeof(a));
> >         strncpy(b, str, sizeof(b) - 1);
> >         printf("String a was %s, b was %s\n", a, b);
> > 
> >         return 0;
> > }

You can't compare user-space code and kernel code, as libc
implementations can differ. For example, snprintf() in user-space may
not NULL-terminate the string while the kernel implementation always does.

> > 
> > diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> > index fdd8327..bede75d 100644
> > --- a/drivers/i2c/busses/i2c-omap.c
> > +++ b/drivers/i2c/busses/i2c-omap.c
> > @@ -879,7 +879,7 @@ omap_i2c_probe(struct platform_device *pdev)
> >  	i2c_set_adapdata(adap, dev);
> >  	adap->owner = THIS_MODULE;
> >  	adap->class = I2C_CLASS_HWMON;
> > -	strncpy(adap->name, "OMAP I2C adapter", sizeof(adap->name));
> > +	strncpy(adap->name, "OMAP I2C adapter", sizeof(adap->name) - 1);
> >  	adap->algo = &omap_i2c_algo;
> >  	adap->dev.parent = &pdev->dev;
> 
> Nack, please just use strlcpy() instead.
> 
> IMHO strncpy() should be banned from the kernel.
> 


-- 
Jean Delvare

Re: [PATCH] i2c: strncpy does not null terminate string

[Roel Kluin]

strlcpy() will always null terminate the string.

Signed-off-by: Roel Kluin <roel.kluin-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
index fdd8327..f2b82ee 100644
--- a/drivers/i2c/busses/i2c-omap.c
+++ b/drivers/i2c/busses/i2c-omap.c
@@ -879,7 +879,7 @@ omap_i2c_probe(struct platform_device *pdev)
 	i2c_set_adapdata(adap, dev);
 	adap->owner = THIS_MODULE;
 	adap->class = I2C_CLASS_HWMON;
-	strncpy(adap->name, "OMAP I2C adapter", sizeof(adap->name));
+	strlcpy(adap->name, "OMAP I2C adapter", sizeof(adap->name));
 	adap->algo = &omap_i2c_algo;
 	adap->dev.parent = &pdev->dev;