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

[Kees Cook <keescook@chromium.org>]

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