sysfs: sysfs_pathname/sysfs_add_one: Use strlcat() instead of strcat()

The warning check for duplicate sysfs entries can cause a buffer overflow
when printing the warning, as strcat() doesn't check buffer sizes.
Use strlcat() instead.

Since strlcat() doesn't return a pointer to the passed buffer, unlike
strcat(), I had to convert the nested concatenation in sysfs_add_one() to
an admittedly more obscure comma operator construct, to avoid emitting code
for the concatenation if CONFIG_BUG is disabled.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/sysfs/dir.c

@@ -485,20 +485,18 @@ int __sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
 /**
  *	sysfs_pathname - return full path to sysfs dirent
  *	@sd: sysfs_dirent whose path we want
- *	@path: caller allocated buffer
+ *	@path: caller allocated buffer of size PATH_MAX
  *
  *	Gives the name "/" to the sysfs_root entry; any path returned
  *	is relative to wherever sysfs is mounted.
- *
- *	XXX: does no error checking on @path size
  */
 static char *sysfs_pathname(struct sysfs_dirent *sd, char *path)
 {
 	if (sd->s_parent) {
 		sysfs_pathname(sd->s_parent, path);
-		strcat(path, "/");
+		strlcat(path, "/", PATH_MAX);
 	}
-	strcat(path, sd->s_name);
+	strlcat(path, sd->s_name, PATH_MAX);
 	return path;
 }
 
@@ -531,9 +529,11 @@ int sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
 		char *path = kzalloc(PATH_MAX, GFP_KERNEL);
 		WARN(1, KERN_WARNING
 		     "sysfs: cannot create duplicate filename '%s'\n",
-		     (path == NULL) ? sd->s_name :
-		     strcat(strcat(sysfs_pathname(acxt->parent_sd, path), "/"),
-		            sd->s_name));
+		     (path == NULL) ? sd->s_name
+				    : (sysfs_pathname(acxt->parent_sd, path),
+				       strlcat(path, "/", PATH_MAX),
+				       strlcat(path, sd->s_name, PATH_MAX),
+				       path));
 		kfree(path);
 	}