Replace $ in page names rather than trying to escape it

Jakub Wilk points out in Debian bug #1021951 that attempting to use the
`--use-backslash` option has a number of complications.  Just replace
dollar signs with question marks instead.

* include/manconfig.h (LESS_OPTS): Revert addition of `--use-backslash`.
* src/man.c: Replace `$` characters with `?` rather than trying to
escape them.
* NEWS.md: Document this.

3 files changed, 15 insertions, 8 deletions

diff --git a/NEWS.md b/NEWS.md
index 0b1e11a1..e64a265c 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -3,8 +3,8 @@ man-db 2.11.1
 
 Fixes:
 
- * SECURITY: Escape `$` characters in page names when constructing `less`
-   prompts.  Note that this requires `less` >= 457 (released in 2012).
+ * SECURITY: Replace `$` characters in page names with `?` when constructing
+   `less` prompts.
  * Silence error message when processing an empty manual page hierarchy with
    a nonexistent cache directory.
  * `man(1)` now sorts whatis references below real pages, even if the whatis
diff --git a/include/manconfig.h b/include/manconfig.h
index 8de135f9..5c2c3189 100644
--- a/include/manconfig.h
+++ b/include/manconfig.h
@@ -106,14 +106,11 @@
  *                (R)aw control chars (but keep track of screen appearance)
  *                (m)ore display style
  *
- * The --use-backslash option allows escaping dollar signs safely in
- * prompts, though requires less >= 457 (released in 2012).
- *
  * If you change this, be sure to match the format with
  * man.c:make_display_command().
  */
 
-#define LESS_OPTS	"--use-backslash -ix8RmPm%s$PM%s$"
+#define LESS_OPTS	"-ix8RmPm%s$PM%s$"
 
 /* This is a minimal latin1 special characters to ascii translation table */
 #if !defined(TR_SET1) || !defined(TR_SET2)
diff --git a/src/man.c b/src/man.c
index 64417f9e..a55aa03a 100644
--- a/src/man.c
+++ b/src/man.c
@@ -873,10 +873,20 @@ static const char *escape_less (const char *string)
 					 2 * strlen (string) + 1);
 
 	while (*string) {
-		if (strchr ("?:.%\\$", *string))
+		char c = *string++;
+
+		if (c == '$')
+			/* Dollar signs are difficult to handle properly, and
+			 * not really worth the trouble, so just replace them
+			 * with question marks.  See
+			 * https://bugs.debian.org/1021951.
+			 */
+			c = '?';
+
+		if (strchr ("?:.%\\", c))
 			*ptr++ = '\\';
 
-		*ptr++ = *string++;
+		*ptr++ = c;
 	}
 
 	*ptr = *string;