blkid: Output non-printing characters using ^ and M- notation

When printing the value of tags in a formatted format, print control
characters and characters with the high eight bit set using the ^ and
M- notation, respectively.  This prevents a filesystem with a garbage
label from potentially screwing up the user's screen (for example,
putting it into graphical mode).

Addresses-Ubuntu-Bug: #78087

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/misc/blkid.c b/misc/blkid.c
index 57cfd1a..c0fda73 100644 (file)
--- a/misc/blkid.c
+++ b/misc/blkid.c
@@ -53,6 +53,31 @@ static void usage(int error)
        exit(error);
 }
 
+/*
+ * This function does "safe" printing.  It will convert non-printable
+ * ASCII characters using '^' and M- notation.
+ */
+static void safe_print(const char *cp, int len)
+{
+       unsigned char   ch;
+
+       if (len < 0)
+               len = strlen(cp);
+
+       while (len--) {
+               ch = *cp++;
+               if (ch > 128) {
+                       fputs("M-", stdout);
+                       ch -= 128;
+               }
+               if ((ch < 32) || (ch == 0x7f)) {
+                       fputc('^', stdout);
+                       ch ^= 0x40; /* ^@, ^A, ^B; ^? for DEL */
+               }
+               fputc(ch, stdout);
+       }
+}
+
 static void print_tags(blkid_dev dev, char *show[], int numtag, int output)
 {
        blkid_tag_iterate       iter;
@@ -76,14 +101,19 @@ static void print_tags(blkid_dev dev, char *show[], int numtag, int output)
                        if (i >= numtag)
                                continue;
                }
-               if (first && !(output & OUTPUT_VALUE_ONLY)) {
-                       printf("%s: ", blkid_dev_devname(dev));
-                       first = 0;
+               if (output & OUTPUT_VALUE_ONLY) {
+                       fputs(value, stdout);
+                       fputc('\n', stdout);
+               } else {
+                       if (first) {
+                               printf("%s: ", blkid_dev_devname(dev));
+                               first = 0;
+                       }
+                       fputs(type, stdout);
+                       fputs("=\"", stdout);
+                       safe_print(value, -1);
+                       fputs("\" ", stdout);
                }
-               if ((output & OUTPUT_VALUE_ONLY))
-                       printf("%s\n", value);
-               else
-                       printf("%s=\"%s\" ", type, value);
        }
        blkid_tag_iterate_end(iter);