[PATCH] Documentation: Fix NUL termination of strncpy

[PATCH] Documentation: Fix NUL termination of strncpy

[Roel Kluin]

Ensure the copied strings are NUL terminated.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
---
 Documentation/accounting/getdelays.c               |    2 +-
 Documentation/hwmon/hpfall.c                       |    2 +-
 Documentation/networking/radiotap-headers.txt      |    2 +-
 .../networking/timestamping/timestamping.c         |    4 ++--
 4 files changed, 5 insertions(+), 5 deletions(-)

Rationale (please correct me if I'm wrong):

For a larger source string, strncpy only NUL terminates when
the size argument is _less_ than sizeof(destination string).
strlcpy does this when it equals sizeof (dest), but does not
overwrite NULs in the higher chars.

Because cpumask is global I used strncpy, for the extra NULs.
devname is local so I think strlcpy can be used.
For {device,hwtstamp}.ifr_name I thought the strlcpy could
be used since ifr_name is zeroed upon creation of device and
hwtstamp.

Oh, and the parenthesis in radiotap-headers.txt should not
be there.

Roel

diff --git a/Documentation/accounting/getdelays.c b/Documentation/accounting/getdelays.c
index 6e25c26..4d71b0e 100644
--- a/Documentation/accounting/getdelays.c
+++ b/Documentation/accounting/getdelays.c
@@ -303,7 +303,7 @@ int main(int argc, char *argv[])
 				err(1, "Invalid rcv buf size\n");
 			break;
 		case 'm':
-			strncpy(cpumask, optarg, sizeof(cpumask));
+			strncpy(cpumask, optarg, sizeof(cpumask) - 1);
 			maskset = 1;
 			printf("cpumask %s maskset %d\n", cpumask, maskset);
 			break;
diff --git a/Documentation/hwmon/hpfall.c b/Documentation/hwmon/hpfall.c
index 681ec22..00477ea 100644
--- a/Documentation/hwmon/hpfall.c
+++ b/Documentation/hwmon/hpfall.c
@@ -27,7 +27,7 @@ int set_unload_heads_path(char *device)
 
 	if (strlen(device) <= 5 || strncmp(device, "/dev/", 5) != 0)
 		return -EINVAL;
-	strncpy(devname, device + 5, sizeof(devname));
+	strlcpy(devname, device + 5, sizeof(devname));
 
 	snprintf(unload_heads_path, sizeof(unload_heads_path),
 				"/sys/block/%s/device/unload_heads", devname);
diff --git a/Documentation/networking/radiotap-headers.txt b/Documentation/networking/radiotap-headers.txt
index 953331c..447e004 100644
--- a/Documentation/networking/radiotap-headers.txt
+++ b/Documentation/networking/radiotap-headers.txt
@@ -126,7 +126,7 @@ int MyFunction(u8 * buf, int buflen)
 
 		case IEEE80211_RADIOTAP_ANTENNA:
 			/* radiotap uses 0 for 1st ant */
-			antenna = *iterator.this_arg);
+			antenna = *iterator.this_arg;
 			break;
 
 		case IEEE80211_RADIOTAP_DBM_TX_POWER:
diff --git a/Documentation/networking/timestamping/timestamping.c b/Documentation/networking/timestamping/timestamping.c
index a7936fe..c1acd2c 100644
--- a/Documentation/networking/timestamping/timestamping.c
+++ b/Documentation/networking/timestamping/timestamping.c
@@ -374,12 +374,12 @@ int main(int argc, char **argv)
 		bail("socket");
 
 	memset(&device, 0, sizeof(device));
-	strncpy(device.ifr_name, interface, sizeof(device.ifr_name));
+	strlcpy(device.ifr_name, interface, sizeof(device.ifr_name));
 	if (ioctl(sock, SIOCGIFADDR, &device) < 0)
 		bail("getting interface IP address");
 
 	memset(&hwtstamp, 0, sizeof(hwtstamp));
-	strncpy(hwtstamp.ifr_name, interface, sizeof(hwtstamp.ifr_name));
+	strlcpy(hwtstamp.ifr_name, interface, sizeof(hwtstamp.ifr_name));
 	hwtstamp.ifr_data = (void *)&hwconfig;
 	memset(&hwconfig, 0, sizeof(hwconfig));
 	hwconfig.tx_type =

Re: [PATCH] Documentation: Fix NUL termination of strncpy

[Roel Kluin]

Ensure the copied strings are NUL terminated.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
---
> Rationale (please correct me if I'm wrong):
> 
> For a larger source string, strncpy only NUL terminates when
> the size argument is _less_ than sizeof(destination string).
> strlcpy does this when it equals sizeof (dest), but does not
> overwrite NULs in the higher chars.
> 
> Because cpumask is global I used strncpy, for the extra NULs.
> devname is local so I think strlcpy can be used.
> For {device,hwtstamp}.ifr_name I thought the strlcpy could
> be used since ifr_name is zeroed upon creation of device and
> hwtstamp.
> 
> Oh, and the parenthesis in radiotap-headers.txt should not
> be there.

See http://markmail.org/message/5ckmbipstgslzolf

(To David Wagner: this was what you meant.)

I forgot strlcpy is not present in old glibc versions,
please use this one instead.

Roel

 Documentation/accounting/getdelays.c               |    2 +-
 Documentation/hwmon/hpfall.c                       |    2 +-
 Documentation/networking/radiotap-headers.txt      |    2 +-
 .../networking/timestamping/timestamping.c         |    4 ++--
 4 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/Documentation/accounting/getdelays.c b/Documentation/accounting/getdelays.c
index 6e25c26..4d71b0e 100644
--- a/Documentation/accounting/getdelays.c
+++ b/Documentation/accounting/getdelays.c
@@ -303,7 +303,7 @@ int main(int argc, char *argv[])
 				err(1, "Invalid rcv buf size\n");
 			break;
 		case 'm':
-			strncpy(cpumask, optarg, sizeof(cpumask));
+			strncpy(cpumask, optarg, sizeof(cpumask) - 1);
 			maskset = 1;
 			printf("cpumask %s maskset %d\n", cpumask, maskset);
 			break;
diff --git a/Documentation/hwmon/hpfall.c b/Documentation/hwmon/hpfall.c
index 681ec22..fbcb585 100644
--- a/Documentation/hwmon/hpfall.c
+++ b/Documentation/hwmon/hpfall.c
@@ -27,7 +27,7 @@ int set_unload_heads_path(char *device)
 
 	if (strlen(device) <= 5 || strncmp(device, "/dev/", 5) != 0)
 		return -EINVAL;
-	strncpy(devname, device + 5, sizeof(devname));
+	strncpy(devname, device + 5, sizeof(devname) - 1);
 
 	snprintf(unload_heads_path, sizeof(unload_heads_path),
 				"/sys/block/%s/device/unload_heads", devname);
diff --git a/Documentation/networking/radiotap-headers.txt b/Documentation/networking/radiotap-headers.txt
index 953331c..447e004 100644
--- a/Documentation/networking/radiotap-headers.txt
+++ b/Documentation/networking/radiotap-headers.txt
@@ -126,7 +126,7 @@ int MyFunction(u8 * buf, int buflen)
 
 		case IEEE80211_RADIOTAP_ANTENNA:
 			/* radiotap uses 0 for 1st ant */
-			antenna = *iterator.this_arg);
+			antenna = *iterator.this_arg;
 			break;
 
 		case IEEE80211_RADIOTAP_DBM_TX_POWER:
diff --git a/Documentation/networking/timestamping/timestamping.c b/Documentation/networking/timestamping/timestamping.c
index a7936fe..bec1f9c 100644
--- a/Documentation/networking/timestamping/timestamping.c
+++ b/Documentation/networking/timestamping/timestamping.c
@@ -374,12 +374,12 @@ int main(int argc, char **argv)
 		bail("socket");
 
 	memset(&device, 0, sizeof(device));
-	strncpy(device.ifr_name, interface, sizeof(device.ifr_name));
+	strncpy(device.ifr_name, interface, sizeof(device.ifr_name) - 1);
 	if (ioctl(sock, SIOCGIFADDR, &device) < 0)
 		bail("getting interface IP address");
 
 	memset(&hwtstamp, 0, sizeof(hwtstamp));
-	strncpy(hwtstamp.ifr_name, interface, sizeof(hwtstamp.ifr_name));
+	strncpy(hwtstamp.ifr_name, interface, sizeof(hwtstamp.ifr_name) - 1);
 	hwtstamp.ifr_data = (void *)&hwconfig;
 	memset(&hwconfig, 0, sizeof(hwconfig));
 	hwconfig.tx_type =

Re: [PATCH] Documentation: Fix NUL termination of strncpy

[Roel Kluin]

Ensure the copied strings are NUL terminated.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
---
>> Rationale (please correct me if I'm wrong):

I was confused. strncpy requires explicit NUL termination
or it depends on a NUL in the source string.

 Documentation/accounting/getdelays.c               |    3 ++-
 Documentation/hwmon/hpfall.c                       |    3 ++-
 Documentation/networking/radiotap-headers.txt      |    2 +-
 .../networking/timestamping/timestamping.c         |    6 ++++--
 4 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/Documentation/accounting/getdelays.c b/Documentation/accounting/getdelays.c
index 6e25c26..ba54b19 100644
--- a/Documentation/accounting/getdelays.c
+++ b/Documentation/accounting/getdelays.c
@@ -303,7 +303,8 @@ int main(int argc, char *argv[])
 				err(1, "Invalid rcv buf size\n");
 			break;
 		case 'm':
-			strncpy(cpumask, optarg, sizeof(cpumask));
+			strncpy(cpumask, optarg, sizeof(cpumask) - 1);
+			cpumask[sizeof(cpumask) - 1] = '\0';
 			maskset = 1;
 			printf("cpumask %s maskset %d\n", cpumask, maskset);
 			break;
diff --git a/Documentation/hwmon/hpfall.c b/Documentation/hwmon/hpfall.c
index 681ec22..4a06c06 100644
--- a/Documentation/hwmon/hpfall.c
+++ b/Documentation/hwmon/hpfall.c
@@ -27,7 +27,8 @@ int set_unload_heads_path(char *device)
 
 	if (strlen(device) <= 5 || strncmp(device, "/dev/", 5) != 0)
 		return -EINVAL;
-	strncpy(devname, device + 5, sizeof(devname));
+	strncpy(devname, device + 5, sizeof(devname) - 1);
+	devname[sizeof(devname) - 1] = '\0';
 
 	snprintf(unload_heads_path, sizeof(unload_heads_path),
 				"/sys/block/%s/device/unload_heads", devname);
diff --git a/Documentation/networking/radiotap-headers.txt b/Documentation/networking/radiotap-headers.txt
index 953331c..447e004 100644
--- a/Documentation/networking/radiotap-headers.txt
+++ b/Documentation/networking/radiotap-headers.txt
@@ -126,7 +126,7 @@ int MyFunction(u8 * buf, int buflen)
 
 		case IEEE80211_RADIOTAP_ANTENNA:
 			/* radiotap uses 0 for 1st ant */
-			antenna = *iterator.this_arg);
+			antenna = *iterator.this_arg;
 			break;
 
 		case IEEE80211_RADIOTAP_DBM_TX_POWER:
diff --git a/Documentation/networking/timestamping/timestamping.c b/Documentation/networking/timestamping/timestamping.c
index a7936fe..e2a17a4 100644
--- a/Documentation/networking/timestamping/timestamping.c
+++ b/Documentation/networking/timestamping/timestamping.c
@@ -374,12 +374,14 @@ int main(int argc, char **argv)
 		bail("socket");
 
 	memset(&device, 0, sizeof(device));
-	strncpy(device.ifr_name, interface, sizeof(device.ifr_name));
+	strncpy(device.ifr_name, interface, sizeof(device.ifr_name) - 1);
+	device.ifr_name[sizeof(device.ifr_name) - 1] = '\0';
 	if (ioctl(sock, SIOCGIFADDR, &device) < 0)
 		bail("getting interface IP address");
 
 	memset(&hwtstamp, 0, sizeof(hwtstamp));
-	strncpy(hwtstamp.ifr_name, interface, sizeof(hwtstamp.ifr_name));
+	strncpy(hwtstamp.ifr_name, interface, sizeof(hwtstamp.ifr_name) - 1);
+	hwtstamp.ifr_name[sizeof(hwtstamp.ifr_name) - 1] = '\0';
 	hwtstamp.ifr_data = (void *)&hwconfig;
 	memset(&hwconfig, 0, sizeof(hwconfig));
 	hwconfig.tx_type =

Re: [PATCH] Documentation: Fix NUL termination of strncpy

[Pádraig Brady]

Roel Kluin wrote:
> Ensure the copied strings are NUL terminated.
> 
> Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
> ---
>> Rationale (please correct me if I'm wrong):
> 
> diff --git a/Documentation/accounting/getdelays.c b/Documentation/accounting/getdelays.c
> index 6e25c26..4d71b0e 100644
> --- a/Documentation/accounting/getdelays.c
> +++ b/Documentation/accounting/getdelays.c
> @@ -303,7 +303,7 @@ int main(int argc, char *argv[])
>  				err(1, "Invalid rcv buf size\n");
>  			break;
>  		case 'm':
> -			strncpy(cpumask, optarg, sizeof(cpumask));
> +			strncpy(cpumask, optarg, sizeof(cpumask) - 1);

You need to explicitly NUL terminate strncpy():
http://www.pixelbeat.org/programming/gcc/string_buffers.html

cheers,
Pádraig.

Re: [PATCH] Documentation: Fix NUL termination of strncpy

[Valdis.Kletnieks]

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On Tue, 17 Nov 2009 12:25:03 GMT, Pádraig Brady said:

> You need to explicitly NUL terminate strncpy():
> http://www.pixelbeat.org/programming/gcc/string_buffers.html

Umm. Actually, no.  It's *nice* if you explicitly do it.  However, it's
not strictly *required*. Consider this code:

struct a {
	int b, c;
	char d[20];
}

bzero(a,sizeof(a)); /* voila! a->d[19] is now a \0 */

Perfectly valid and we do it all the time. Your referenced web page comments
that using memset() or bzero() is inefficient - I wonder if they actually
*tested* the difference between using one memset() or bzero() on a large
structure compared to lots and lots of explicit initialization statements
(i-cache issues probably most important there). The downside is that there's a
greater chance of some programmer refactoring code and bollixing it up. (The
astute reader will remember a short thread about this not too long ago.. :)

And if you're truly careful and always use the strn- variants of the string
functions, it's actually possible to *not* null-terminate the strings.  But
it results in very brittle code and makes Baby Andrew cry, mostly because when
somebody adds a printf() to debug the brittle code, it suddenly becomes even
more brittle... :) 

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