ipmi: refactor deprecated strncpy

`strncpy` is deprecated for use on NUL-terminated destination strings [1].

In this case, strncpy is being used specifically for its NUL-padding
behavior (and has been commented as such). Moreover, the destination
string is not required to be NUL-terminated [2].

We can use a more robust and less ambiguous interface in
`memcpy_and_pad` which makes the code more readable and even eliminates
the need for that comment.

Let's also use `strnlen` instead of `strlen()` with an upper-bounds
check as this is intrinsically a part of `strnlen`.

Also included in this patch is a simple 1:1 change of `strncpy` to
`strscpy` for ipmi_ssif.c. If NUL-padding is wanted here as well then we
should opt again for `strscpy_pad`.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://lore.kernel.org/all/ZQEADYBl0uZ1nX60@mail.minyard.net/ [2]
Link: KSPP#90
Cc: linux-hardening@vger.kernel.org
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
Message-Id: <20230913-strncpy-drivers-char-ipmi-ipmi-v2-1-e3bc0f6e599f@google.com>
Signed-off-by: Corey Minyard <minyard@acm.org>

Author: JustinStitt

drivers/char/ipmi/ipmi_msghandler.c

@@ -5377,20 +5377,15 @@ static void send_panic_events(struct ipmi_smi *intf, char *str)
 
 	j = 0;
 	while (*p) {
-		int size = strlen(p);
+		int size = strnlen(p, 11);
 
-		if (size > 11)
-			size = 11;
 		data[0] = 0;
 		data[1] = 0;
 		data[2] = 0xf0; /* OEM event without timestamp. */
 		data[3] = intf->addrinfo[0].address;
 		data[4] = j++; /* sequence # */
-		/*
-		 * Always give 11 bytes, so strncpy will fill
-		 * it with zeroes for me.
-		 */
-		strncpy(data+5, p, 11);
+
+		memcpy_and_pad(data+5, 11, p, size, '\0');
 		p += size;
 
 		ipmi_panic_request_and_wait(intf, &addr, &msg);

drivers/char/ipmi/ipmi_ssif.c

@@ -1945,7 +1945,7 @@ static int new_ssif_client(int addr, char *adapter_name,
 		}
 	}
 
-	strncpy(addr_info->binfo.type, DEVICE_NAME,
+	strscpy(addr_info->binfo.type, DEVICE_NAME,
 		sizeof(addr_info->binfo.type));
 	addr_info->binfo.addr = addr;
 	addr_info->binfo.platform_data = addr_info;