mntent: fields are delimited only by tabs or spaces, not general whitespace

this matters because the kernel-provided mtab only escapes tabs,
spaces, newlines, and backslashes. it leaves carriage returns, form
feeds, and vertical tabs literal.

src/misc/mntent.c

@@ -81,7 +81,7 @@ struct mntent *getmntent_r(FILE *f, struct mntent *mnt, char *linebuf, int bufle
 		len = strlen(linebuf);
 		if (len > INT_MAX) continue;
 		for (i = 0; i < sizeof n / sizeof *n; i++) n[i] = len;
-		sscanf(linebuf, " %n%*s%n %n%*s%n %n%*s%n %n%*s%n %d %d",
+		sscanf(linebuf, " %n%*[^ \t]%n %n%*[^ \t]%n %n%*[^ \t]%n %n%*[^ \t]%n %d %d",
 			n, n+1, n+2, n+3, n+4, n+5, n+6, n+7,
 			&mnt->mnt_freq, &mnt->mnt_passno);
 	} while (linebuf[n[0]] == '#' || n[1]==len);