[PATCH] firmware: dmi: Respect buffer size in get_modalias

[Cyrill Gorcunov <gorcunov@gmail.com>]

When we collect data from DMI data the result is accumulated either
in a page buffer from sysfs entry or from uevent environment buffer.
Both are big enough (4K and 2K) and it is hard to imagine that we
overflow 4K page with the data, still the situation is different for
uevent buffer where buffer may be already filled with data and we
possibly may overflow it.

Thus lets respect buffer size given by a caller and never write
data unconditionally.

CC: Jean Delvare <jdelvare@suse.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
---
 drivers/firmware/dmi-id.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

Index: linux-tip.git/drivers/firmware/dmi-id.c
===================================================================
--- linux-tip.git.orig/drivers/firmware/dmi-id.c
+++ linux-tip.git/drivers/firmware/dmi-id.c
@@ -103,8 +103,12 @@ static ssize_t get_modalias(char *buffer
 	char *p;
 	const struct mafield *f;
 
-	strcpy(buffer, "dmi");
-	p = buffer + 3; left = buffer_size - 4;
+	l = strscpy(buffer, "dmi", buffer_size);
+	if (l < 0)
+		return 0;
+	p = buffer + l; left = buffer_size - l - 1;
+	if (left < 0)
+		return 0;
 
 	for (f = fields; f->prefix && left > 0; f++) {
 		const char *c;
@@ -135,7 +139,7 @@ static ssize_t sys_dmi_modalias_show(str
 				     struct device_attribute *attr, char *page)
 {
 	ssize_t r;
-	r = get_modalias(page, PAGE_SIZE-1);
+	r = get_modalias(page, PAGE_SIZE-2);
 	page[r] = '\n';
 	page[r+1] = 0;
 	return r+1;
@@ -163,7 +167,7 @@ static int dmi_dev_uevent(const struct d
 		return -ENOMEM;
 	len = get_modalias(&env->buf[env->buflen - 1],
 			   sizeof(env->buf) - env->buflen);
-	if (len >= (sizeof(env->buf) - env->buflen))
+	if (!len || len >= (sizeof(env->buf) - env->buflen))
 		return -ENOMEM;
 	env->buflen += len;
 	return 0;