EDAC/mc: Replace strcpy(), sprintf() and snprintf() with strscpy() or scnprintf()

strcpy() performs no bounds checking on the destination buffer. This
could result in linear overflows beyond the end of the buffer, leading
to all kinds of misbehavior. The safe replacement is strscpy().
[1][2]

However, to simplify and clarify the code, to concatenate labels use the
scnprintf() function. This way it is not necessary to check the return
value of strscpy() (-E2BIG if the parameter count is 0 or the src was
truncated) since scnprintf() always returns the number of chars written
into the buffer. This function always returns a nul-terminated string
even if it needs to be truncated.

While at it, fix all other broken string generation code that wrongly
interprets snprintf()'s return code or just uses sprintf(), implement
that using scnprintf() here too. Drop breaks in loops around
scnprintf() as it is safe now to loop.

Moreover, the check is not needed: for the case when the buffer is
exhausted, len never gets zero because scnprintf() takes the full buffer
length as input parameter, but excludes the trailing '\0' in its return
code and thus, 1 is the minimum len.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strcpy
[2] https://github.com/KSPP/linux/issues/88

[ rric: Replace snprintf() with scnprintf(), rework sprintf() user,
drop breaks in loops around scnprintf(), introduce 'end' pointer to
reduce pointer arithmetic, use prefix pattern for e->location,
adjust subject and description ]

Co-developed-by: Joe Perches <[e-mail]>
Signed-off-by: Joe Perches <[e-mail]>
Signed-off-by: Len Baker <[e-mail]>
Signed-off-by: Robert Richter <[e-mail]>
Signed-off-by: Borislav Petkov <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

drivers/edac/edac_mc.c

···
 	char *p = buf;
 
 	for (i = 0; i < mci->n_layers; i++) {
-		n = snprintf(p, len, "%s %d ",
+		n = scnprintf(p, len, "%s %d ",
 			      edac_layer_name[mci->layers[i].type],
 			      dimm->location[i]);
 		p += n;
 		len -= n;
 		count += n;
-		if (!len)
-			break;
 	}
 
 	return count;
···
 		 */
 		len = sizeof(dimm->label);
 		p = dimm->label;
-		n = snprintf(p, len, "mc#%u", mci->mc_idx);
+		n = scnprintf(p, len, "mc#%u", mci->mc_idx);
 		p += n;
 		len -= n;
 		for (layer = 0; layer < mci->n_layers; layer++) {
-			n = snprintf(p, len, "%s#%u",
-				     edac_layer_name[mci->layers[layer].type],
-				     pos[layer]);
+			n = scnprintf(p, len, "%s#%u",
+				      edac_layer_name[mci->layers[layer].type],
+				      pos[layer]);
 			p += n;
 			len -= n;
 			dimm->location[layer] = pos[layer];
-
-			if (len <= 0)
-				break;
 		}
 
 		/* Link it to the csrows old API data */
···
 			  const char *other_detail)
 {
 	struct dimm_info *dimm;
-	char *p;
+	char *p, *end;
 	int row = -1, chan = -1;
 	int pos[EDAC_MAX_LAYERS] = { top_layer, mid_layer, low_layer };
 	int i, n_labels = 0;
 	struct edac_raw_error_desc *e = &mci->error_desc;
 	bool any_memory = true;
+	const char *prefix;
 
 	edac_dbg(3, "MC%d\n", mci->mc_idx);
 
···
 	 */
 	p = e->label;
 	*p = '\0';
+	end = p + sizeof(e->label);
+	prefix = "";
 
 	mci_for_each_dimm(mci, dimm) {
 		if (top_layer >= 0 && top_layer != dimm->location[0])
···
 			p = e->label;
 			*p = '\0';
 		} else {
-			if (p != e->label) {
-				strcpy(p, OTHER_LABEL);
-				p += strlen(OTHER_LABEL);
-			}
-			strcpy(p, dimm->label);
-			p += strlen(p);
+			p += scnprintf(p, end - p, "%s%s", prefix, dimm->label);
+			prefix = OTHER_LABEL;
 		}
 
 		/*
···
 	}
 
 	if (any_memory)
-		strcpy(e->label, "any memory");
+		strscpy(e->label, "any memory", sizeof(e->label));
 	else if (!*e->label)
-		strcpy(e->label, "unknown memory");
+		strscpy(e->label, "unknown memory", sizeof(e->label));
 
 	edac_inc_csrow(e, row, chan);
 
 	/* Fill the RAM location data */
 	p = e->location;
+	end = p + sizeof(e->location);
+	prefix = "";
 
 	for (i = 0; i < mci->n_layers; i++) {
 		if (pos[i] < 0)
 			continue;
 
-		p += sprintf(p, "%s:%d ",
-			     edac_layer_name[mci->layers[i].type],
-			     pos[i]);
+		p += scnprintf(p, end - p, "%s%s:%d", prefix,
+			       edac_layer_name[mci->layers[i].type], pos[i]);
+		prefix = " ";
 	}
-	if (p > e->location)
-		*(p - 1) = '\0';
 
 	edac_raw_mc_handle_error(e);
 }