[PATCH] clean up scary strncpy(dst, src, strlen(src)) uses

[PATCH] clean up scary strncpy(dst, src, strlen(src)) uses

[Kees Cook]

Fix various weird constructions of strncpy(dst, src, strlen(src)). Length
limits should be about the space available in the destination, not
repurposed as a method to either always include or always exclude
a trailing NULL byte. Either the NULL should always be copied
(using strlcpy), or it should not be copied (using something like
memcpy). Readable code should not depend on the weird behavior of strncpy
when it hits the length limit. Better to avoid the anti-pattern entirely.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
This is a follow-up to the anti-pattern being fixed in iscsi-target,
which was exploitable:
"iscsi-target: fix heap buffer overflow on error"
http://git.kernel.org/cgit/linux/kernel/git/nab/target-pending.git/commit/?id=cea4dcfdad926a27a18e188720efe0f2c9403456
---
 Documentation/accounting/getdelays.c             |    3 ++-
 drivers/acpi/sysfs.c                             |    3 +--
 drivers/s390/net/qeth_l3_sys.c                   |    6 ++----
 drivers/staging/tidspbridge/rmgr/drv_interface.c |    3 +--
 fs/hppfs/hppfs.c                                 |   11 ++++++-----
 5 files changed, 12 insertions(+), 14 deletions(-)

diff --git a/Documentation/accounting/getdelays.c b/Documentation/accounting/getdelays.c
index f8ebcde..5e4773d 100644
--- a/Documentation/accounting/getdelays.c
+++ b/Documentation/accounting/getdelays.c
@@ -23,6 +23,7 @@
 #include <sys/socket.h>
 #include <sys/wait.h>
 #include <signal.h>
+#include <bsd/string.h>
 
 #include <linux/genetlink.h>
 #include <linux/taskstats.h>
@@ -299,7 +300,7 @@ int main(int argc, char *argv[])
 			break;
 		case 'C':
 			containerset = 1;
-			strncpy(containerpath, optarg, strlen(optarg) + 1);
+			strlcpy(containerpath, optarg, sizeof(containerpath));
 			break;
 		case 'w':
 			logfile = strdup(optarg);
diff --git a/drivers/acpi/sysfs.c b/drivers/acpi/sysfs.c
index fcae5fa..193745d 100644
--- a/drivers/acpi/sysfs.c
+++ b/drivers/acpi/sysfs.c
@@ -677,10 +677,9 @@ void acpi_irq_stats_init(void)
 		else
 			sprintf(buffer, "bug%02X", i);
 
-		name = kzalloc(strlen(buffer) + 1, GFP_KERNEL);
+		name = kstrdup(buffer, GFP_KERNEL);
 		if (name == NULL)
 			goto fail;
-		strncpy(name, buffer, strlen(buffer) + 1);
 
 		sysfs_attr_init(&counter_attrs[i].attr);
 		counter_attrs[i].attr.name = name;
diff --git a/drivers/s390/net/qeth_l3_sys.c b/drivers/s390/net/qeth_l3_sys.c
index e70af24..d1c8025 100644
--- a/drivers/s390/net/qeth_l3_sys.c
+++ b/drivers/s390/net/qeth_l3_sys.c
@@ -315,10 +315,8 @@ static ssize_t qeth_l3_dev_hsuid_store(struct device *dev,
 	if (qeth_configure_cq(card, QETH_CQ_ENABLED))
 		return -EPERM;
 
-	for (i = 0; i < 8; i++)
-		card->options.hsuid[i] = ' ';
-	card->options.hsuid[8] = '\0';
-	strncpy(card->options.hsuid, tmp, strlen(tmp));
+	snprintf(card->options.hsuid, sizeof(card->options.hsuid),
+		 "%-8s", tmp);
 	ASCEBC(card->options.hsuid, 8);
 	if (card->dev)
 		memcpy(card->dev->perm_addr, card->options.hsuid, 9);
diff --git a/drivers/staging/tidspbridge/rmgr/drv_interface.c b/drivers/staging/tidspbridge/rmgr/drv_interface.c
index df0f37e..c4d632c 100644
--- a/drivers/staging/tidspbridge/rmgr/drv_interface.c
+++ b/drivers/staging/tidspbridge/rmgr/drv_interface.c
@@ -421,12 +421,11 @@ static int omap3_bridge_startup(struct platform_device *pdev)
 	drv_datap->tc_wordswapon = tc_wordswapon;
 
 	if (base_img) {
-		drv_datap->base_img = kmalloc(strlen(base_img) + 1, GFP_KERNEL);
+		drv_datap->base_img = kstrdup(base_img, GFP_KERNEL);
 		if (!drv_datap->base_img) {
 			err = -ENOMEM;
 			goto err2;
 		}
-		strncpy(drv_datap->base_img, base_img, strlen(base_img) + 1);
 	}
 
 	dev_set_drvdata(bridge, drv_datap);
diff --git a/fs/hppfs/hppfs.c b/fs/hppfs/hppfs.c
index cd3e389..d619b83 100644
--- a/fs/hppfs/hppfs.c
+++ b/fs/hppfs/hppfs.c
@@ -69,7 +69,7 @@ static char *dentry_name(struct dentry *dentry, int extra)
 	struct dentry *parent;
 	char *root, *name;
 	const char *seg_name;
-	int len, seg_len;
+	int len, seg_len, root_len;
 
 	len = 0;
 	parent = dentry;
@@ -81,7 +81,8 @@ static char *dentry_name(struct dentry *dentry, int extra)
 	}
 
 	root = "proc";
-	len += strlen(root);
+	root_len = strlen(root);
+	len += root_len;
 	name = kmalloc(len + extra + 1, GFP_KERNEL);
 	if (name == NULL)
 		return NULL;
@@ -91,7 +92,7 @@ static char *dentry_name(struct dentry *dentry, int extra)
 	while (parent->d_parent != parent) {
 		if (is_pid(parent)) {
 			seg_name = "pid";
-			seg_len = strlen("pid");
+			seg_len = strlen(seg_name);
 		}
 		else {
 			seg_name = parent->d_name.name;
@@ -100,10 +101,10 @@ static char *dentry_name(struct dentry *dentry, int extra)
 
 		len -= seg_len + 1;
 		name[len] = '/';
-		strncpy(&name[len + 1], seg_name, seg_len);
+		memcpy(&name[len + 1], seg_name, seg_len);
 		parent = parent->d_parent;
 	}
-	strncpy(name, root, strlen(root));
+	memcpy(name, root, root_len);
 	return name;
 }
 
-- 
1.7.9.5


-- 
Kees Cook
Chrome OS Security

Re: [PATCH] clean up scary strncpy(dst, src, strlen(src)) uses

[Greg KH]

On Fri, May 31, 2013 at 09:18:07AM -0700, Kees Cook wrote:
> Fix various weird constructions of strncpy(dst, src, strlen(src)). Length
> limits should be about the space available in the destination, not
> repurposed as a method to either always include or always exclude
> a trailing NULL byte. Either the NULL should always be copied
> (using strlcpy), or it should not be copied (using something like
> memcpy). Readable code should not depend on the weird behavior of strncpy
> when it hits the length limit. Better to avoid the anti-pattern entirely.
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> This is a follow-up to the anti-pattern being fixed in iscsi-target,
> which was exploitable:
> "iscsi-target: fix heap buffer overflow on error"
> http://git.kernel.org/cgit/linux/kernel/git/nab/target-pending.git/commit/?id=cea4dcfdad926a27a18e188720efe0f2c9403456
> ---
>  Documentation/accounting/getdelays.c             |    3 ++-
>  drivers/acpi/sysfs.c                             |    3 +--
>  drivers/s390/net/qeth_l3_sys.c                   |    6 ++----
>  drivers/staging/tidspbridge/rmgr/drv_interface.c |    3 +--

For the drivers/staging/ part of this:

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Re: [PATCH] clean up scary strncpy(dst, src, strlen(src)) uses

[Rafael J. Wysocki]

On Friday, May 31, 2013 09:18:07 AM Kees Cook wrote:
> Fix various weird constructions of strncpy(dst, src, strlen(src)). Length
> limits should be about the space available in the destination, not
> repurposed as a method to either always include or always exclude
> a trailing NULL byte. Either the NULL should always be copied
> (using strlcpy), or it should not be copied (using something like
> memcpy). Readable code should not depend on the weird behavior of strncpy
> when it hits the length limit. Better to avoid the anti-pattern entirely.
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>

For the ACPI part:

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

> ---
> This is a follow-up to the anti-pattern being fixed in iscsi-target,
> which was exploitable:
> "iscsi-target: fix heap buffer overflow on error"
> http://git.kernel.org/cgit/linux/kernel/git/nab/target-pending.git/commit/?id=cea4dcfdad926a27a18e188720efe0f2c9403456
> ---
>  Documentation/accounting/getdelays.c             |    3 ++-
>  drivers/acpi/sysfs.c                             |    3 +--
>  drivers/s390/net/qeth_l3_sys.c                   |    6 ++----
>  drivers/staging/tidspbridge/rmgr/drv_interface.c |    3 +--
>  fs/hppfs/hppfs.c                                 |   11 ++++++-----
>  5 files changed, 12 insertions(+), 14 deletions(-)
> 
> diff --git a/Documentation/accounting/getdelays.c b/Documentation/accounting/getdelays.c
> index f8ebcde..5e4773d 100644
> --- a/Documentation/accounting/getdelays.c
> +++ b/Documentation/accounting/getdelays.c
> @@ -23,6 +23,7 @@
>  #include <sys/socket.h>
>  #include <sys/wait.h>
>  #include <signal.h>
> +#include <bsd/string.h>
>  
>  #include <linux/genetlink.h>
>  #include <linux/taskstats.h>
> @@ -299,7 +300,7 @@ int main(int argc, char *argv[])
>  			break;
>  		case 'C':
>  			containerset = 1;
> -			strncpy(containerpath, optarg, strlen(optarg) + 1);
> +			strlcpy(containerpath, optarg, sizeof(containerpath));
>  			break;
>  		case 'w':
>  			logfile = strdup(optarg);
> diff --git a/drivers/acpi/sysfs.c b/drivers/acpi/sysfs.c
> index fcae5fa..193745d 100644
> --- a/drivers/acpi/sysfs.c
> +++ b/drivers/acpi/sysfs.c
> @@ -677,10 +677,9 @@ void acpi_irq_stats_init(void)
>  		else
>  			sprintf(buffer, "bug%02X", i);
>  
> -		name = kzalloc(strlen(buffer) + 1, GFP_KERNEL);
> +		name = kstrdup(buffer, GFP_KERNEL);
>  		if (name == NULL)
>  			goto fail;
> -		strncpy(name, buffer, strlen(buffer) + 1);
>  
>  		sysfs_attr_init(&counter_attrs[i].attr);
>  		counter_attrs[i].attr.name = name;
> diff --git a/drivers/s390/net/qeth_l3_sys.c b/drivers/s390/net/qeth_l3_sys.c
> index e70af24..d1c8025 100644
> --- a/drivers/s390/net/qeth_l3_sys.c
> +++ b/drivers/s390/net/qeth_l3_sys.c
> @@ -315,10 +315,8 @@ static ssize_t qeth_l3_dev_hsuid_store(struct device *dev,
>  	if (qeth_configure_cq(card, QETH_CQ_ENABLED))
>  		return -EPERM;
>  
> -	for (i = 0; i < 8; i++)
> -		card->options.hsuid[i] = ' ';
> -	card->options.hsuid[8] = '\0';
> -	strncpy(card->options.hsuid, tmp, strlen(tmp));
> +	snprintf(card->options.hsuid, sizeof(card->options.hsuid),
> +		 "%-8s", tmp);
>  	ASCEBC(card->options.hsuid, 8);
>  	if (card->dev)
>  		memcpy(card->dev->perm_addr, card->options.hsuid, 9);
> diff --git a/drivers/staging/tidspbridge/rmgr/drv_interface.c b/drivers/staging/tidspbridge/rmgr/drv_interface.c
> index df0f37e..c4d632c 100644
> --- a/drivers/staging/tidspbridge/rmgr/drv_interface.c
> +++ b/drivers/staging/tidspbridge/rmgr/drv_interface.c
> @@ -421,12 +421,11 @@ static int omap3_bridge_startup(struct platform_device *pdev)
>  	drv_datap->tc_wordswapon = tc_wordswapon;
>  
>  	if (base_img) {
> -		drv_datap->base_img = kmalloc(strlen(base_img) + 1, GFP_KERNEL);
> +		drv_datap->base_img = kstrdup(base_img, GFP_KERNEL);
>  		if (!drv_datap->base_img) {
>  			err = -ENOMEM;
>  			goto err2;
>  		}
> -		strncpy(drv_datap->base_img, base_img, strlen(base_img) + 1);
>  	}
>  
>  	dev_set_drvdata(bridge, drv_datap);
> diff --git a/fs/hppfs/hppfs.c b/fs/hppfs/hppfs.c
> index cd3e389..d619b83 100644
> --- a/fs/hppfs/hppfs.c
> +++ b/fs/hppfs/hppfs.c
> @@ -69,7 +69,7 @@ static char *dentry_name(struct dentry *dentry, int extra)
>  	struct dentry *parent;
>  	char *root, *name;
>  	const char *seg_name;
> -	int len, seg_len;
> +	int len, seg_len, root_len;
>  
>  	len = 0;
>  	parent = dentry;
> @@ -81,7 +81,8 @@ static char *dentry_name(struct dentry *dentry, int extra)
>  	}
>  
>  	root = "proc";
> -	len += strlen(root);
> +	root_len = strlen(root);
> +	len += root_len;
>  	name = kmalloc(len + extra + 1, GFP_KERNEL);
>  	if (name == NULL)
>  		return NULL;
> @@ -91,7 +92,7 @@ static char *dentry_name(struct dentry *dentry, int extra)
>  	while (parent->d_parent != parent) {
>  		if (is_pid(parent)) {
>  			seg_name = "pid";
> -			seg_len = strlen("pid");
> +			seg_len = strlen(seg_name);
>  		}
>  		else {
>  			seg_name = parent->d_name.name;
> @@ -100,10 +101,10 @@ static char *dentry_name(struct dentry *dentry, int extra)
>  
>  		len -= seg_len + 1;
>  		name[len] = '/';
> -		strncpy(&name[len + 1], seg_name, seg_len);
> +		memcpy(&name[len + 1], seg_name, seg_len);
>  		parent = parent->d_parent;
>  	}
> -	strncpy(name, root, strlen(root));
> +	memcpy(name, root, root_len);
>  	return name;
>  }
>  
> 
-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

Re: [PATCH] clean up scary strncpy(dst, src, strlen(src)) uses

[Andrew Morton]

On Fri, 31 May 2013 09:18:07 -0700 Kees Cook <keescook@chromium.org> wrote:

> Fix various weird constructions of strncpy(dst, src, strlen(src)). Length
> limits should be about the space available in the destination, not
> repurposed as a method to either always include or always exclude
> a trailing NULL byte. Either the NULL should always be copied
> (using strlcpy), or it should not be copied (using something like
> memcpy). Readable code should not depend on the weird behavior of strncpy
> when it hits the length limit. Better to avoid the anti-pattern entirely.
> 
> ...
>
> --- a/Documentation/accounting/getdelays.c
> +++ b/Documentation/accounting/getdelays.c
> @@ -23,6 +23,7 @@
>  #include <sys/socket.h>
>  #include <sys/wait.h>
>  #include <signal.h>
> +#include <bsd/string.h>
>  
>  #include <linux/genetlink.h>
>  #include <linux/taskstats.h>
> @@ -299,7 +300,7 @@ int main(int argc, char *argv[])
>  			break;
>  		case 'C':
>  			containerset = 1;
> -			strncpy(containerpath, optarg, strlen(optarg) + 1);
> +			strlcpy(containerpath, optarg, sizeof(containerpath));
>  			break;
>  		case 'w':
>  			logfile = strdup(optarg);

Documentation/accounting/getdelays.c:26:24: fatal error: bsd/string.h: No such file or directory

I'll revert this part.

Re: [PATCH] clean up scary strncpy(dst, src, strlen(src)) uses

[Kees Cook]

On Wed, Jun 5, 2013 at 4:48 PM, Andrew Morton <akpm@linux-foundation.org> wrote:
> On Fri, 31 May 2013 09:18:07 -0700 Kees Cook <keescook@chromium.org> wrote:
>
>> Fix various weird constructions of strncpy(dst, src, strlen(src)). Length
>> limits should be about the space available in the destination, not
>> repurposed as a method to either always include or always exclude
>> a trailing NULL byte. Either the NULL should always be copied
>> (using strlcpy), or it should not be copied (using something like
>> memcpy). Readable code should not depend on the weird behavior of strncpy
>> when it hits the length limit. Better to avoid the anti-pattern entirely.
>>
>> ...
>>
>> --- a/Documentation/accounting/getdelays.c
>> +++ b/Documentation/accounting/getdelays.c
>> @@ -23,6 +23,7 @@
>>  #include <sys/socket.h>
>>  #include <sys/wait.h>
>>  #include <signal.h>
>> +#include <bsd/string.h>
>>
>>  #include <linux/genetlink.h>
>>  #include <linux/taskstats.h>
>> @@ -299,7 +300,7 @@ int main(int argc, char *argv[])
>>                       break;
>>               case 'C':
>>                       containerset = 1;
>> -                     strncpy(containerpath, optarg, strlen(optarg) + 1);
>> +                     strlcpy(containerpath, optarg, sizeof(containerpath));
>>                       break;
>>               case 'w':
>>                       logfile = strdup(optarg);
>
> Documentation/accounting/getdelays.c:26:24: fatal error: bsd/string.h: No such file or directory
>
> I'll revert this part.

Ah, hrm. Well, in that case, it should use strdup, as logfile does
already. Do you want me to send a patch for that?

-Kees

--
Kees Cook
Chrome OS Security

Re: [PATCH] clean up scary strncpy(dst, src, strlen(src)) uses

[Geert Uytterhoeven]

On Thu, Jun 6, 2013 at 1:48 AM, Andrew Morton <akpm@linux-foundation.org> wrote:
>> -                     strncpy(containerpath, optarg, strlen(optarg) + 1);
>> +                     strlcpy(containerpath, optarg, sizeof(containerpath));
>>                       break;
>>               case 'w':
>>                       logfile = strdup(optarg);
>
> Documentation/accounting/getdelays.c:26:24: fatal error: bsd/string.h: No such file or directory

sudo apt-get install libbsd-dev

strlcpy() is available almost everywhere, except in glibc, cfr.
http://en.wikibooks.org/wiki/C_Programming/C_Reference/nonstandard/strlcpy#Criticism

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds