vmcore: replace strncpy with strscpy_pad

strncpy() is in the process of being replaced as it is deprecated [1].
We should move towards safer and less ambiguous string interfaces.

Looking at vmcoredd_header's definition:
|	struct vmcoredd_header {
|		__u32 n_namesz; /* Name size */
|		__u32 n_descsz; /* Content size */
|		__u32 n_type;   /* NT_VMCOREDD */
|		__u8 name[8];   /* LINUX\0\0\0 */
|		__u8 dump_name[VMCOREDD_MAX_NAME_BYTES]; /* Device dump's name */
|	};
.. we see that @name wants to be NUL-padded.

We're copying data->dump_name which is defined as:
|	char dump_name[VMCOREDD_MAX_NAME_BYTES]; /* Unique name of the dump */
.. which shares the same size as vdd_hdr->dump_name. Let's make sure we
NUL-pad this as well.

Use strscpy_pad() which NUL-terminates and NUL-pads its destination
buffers. Specifically, use the new 2-argument version of strscpy_pad
introduced in Commit e6584c3 ("string: Allow 2-argument
strscpy()").

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: KSPP#90
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Justin Stitt <[email protected]>
Acked-by: Baoquan He <[email protected]>
Cc: Dave Young <[email protected]>
Cc: Vivek Goyal <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: JustinStitt

fs/proc/vmcore.c

@@ -1370,9 +1370,8 @@ static void vmcoredd_write_header(void *buf, struct vmcoredd_data *data,
 	vdd_hdr->n_descsz = size + sizeof(vdd_hdr->dump_name);
 	vdd_hdr->n_type = NT_VMCOREDD;
 
-	strncpy((char *)vdd_hdr->name, VMCOREDD_NOTE_NAME,
-		sizeof(vdd_hdr->name));
-	memcpy(vdd_hdr->dump_name, data->dump_name, sizeof(vdd_hdr->dump_name));
+	strscpy_pad(vdd_hdr->name, VMCOREDD_NOTE_NAME);
+	strscpy_pad(vdd_hdr->dump_name, data->dump_name);
 }
 
 /**