net: pktgen: fix access outside of user given buffer in pktgen_thread_write()

jira VULN-70907
cve CVE-2025-38061
commit-author Peter Seiderer <ps.report@gmx.net>
commit 425e644

Honour the user given buffer size for the strn_len() calls (otherwise
strn_len() will access memory outside of the user given buffer).

	Signed-off-by: Peter Seiderer <ps.report@gmx.net>
	Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250219084527.20488-8-ps.report@gmx.net
	Signed-off-by: Jakub Kicinski <kuba@kernel.org>
(cherry picked from commit 425e644)
	Signed-off-by: Marcin Wcisło <marcin.wcislo@conclusive.pl>

Author: pvts-mat

net/core/pktgen.c

@@ -1777,8 +1777,8 @@ static ssize_t pktgen_thread_write(struct file *file,
 	i = len;
 
 	/* Read variable name */
-
-	len = strn_len(&user_buffer[i], sizeof(name) - 1);
+	max = min(sizeof(name) - 1, count - i);
+	len = strn_len(&user_buffer[i], max);
 	if (len < 0)
 		return len;
 
@@ -1808,7 +1808,8 @@ static ssize_t pktgen_thread_write(struct file *file,
 	if (!strcmp(name, "add_device")) {
 		char f[32];
 		memset(f, 0, 32);
-		len = strn_len(&user_buffer[i], sizeof(f) - 1);
+		max = min(sizeof(f) - 1, count - i);
+		len = strn_len(&user_buffer[i], max);
 		if (len < 0) {
 			ret = len;
 			goto out;