fix: pem parsing should allow single dashes in comments

stuffer/s2n_stuffer_pem.c

@@ -20,8 +20,9 @@
 #include "stuffer/s2n_stuffer.h"
 #include "utils/s2n_safety.h"
 
-#define S2N_PEM_DELIMTER_CHAR         '-'
-#define S2N_PEM_DELIMITER_MIN_COUNT   1
+#define S2N_PEM_DELIMITER_CHAR        '-'
+#define S2N_PEM_DELIMITER_TOKEN       "--"
+#define S2N_PEM_DELIMITER_MIN_COUNT   2
 #define S2N_PEM_DELIMITER_MAX_COUNT   64
 #define S2N_PEM_BEGIN_TOKEN           "BEGIN "
 #define S2N_PEM_END_TOKEN             "END "
@@ -36,21 +37,26 @@
 static int s2n_stuffer_pem_read_encapsulation_line(struct s2n_stuffer *pem, const char *encap_marker,
         const char *keyword)
 {
-    /* Skip any number of Chars until a "-" is reached */
-    POSIX_GUARD(s2n_stuffer_skip_to_char(pem, S2N_PEM_DELIMTER_CHAR));
+    /* Skip any number of Chars until a "--" is reached.
+     * We use "--" instead of "-" to account for dashes that appear in comments.
+     * We do not accept comments that contain "--".
+     */
+    POSIX_GUARD(s2n_stuffer_skip_read_until(pem, S2N_PEM_DELIMITER_TOKEN));
 
-    /* Ensure between 1 and 64 '-' chars at start of line */
-    POSIX_GUARD(s2n_stuffer_skip_expected_char(pem, S2N_PEM_DELIMTER_CHAR, S2N_PEM_DELIMITER_MIN_COUNT,
-            S2N_PEM_DELIMITER_MAX_COUNT, NULL));
+    /* Ensure between 2 and 64 '-' chars at start of line.
+     * We already read 2 '-' chars when we read the S2N_PEM_DELIMITER_TOKEN.
+     */
+    POSIX_GUARD(s2n_stuffer_skip_expected_char(pem, S2N_PEM_DELIMITER_CHAR, 0,
+            S2N_PEM_DELIMITER_MAX_COUNT - 2, NULL));
 
     /* Ensure next string in stuffer is "BEGIN " or "END " */
     POSIX_GUARD(s2n_stuffer_read_expected_str(pem, encap_marker));
 
     /* Ensure next string is stuffer is the keyword (Eg "CERTIFICATE", "PRIVATE KEY", etc) */
     POSIX_GUARD(s2n_stuffer_read_expected_str(pem, keyword));
 
-    /* Ensure between 1 and 64 '-' chars at end of line */
-    POSIX_GUARD(s2n_stuffer_skip_expected_char(pem, S2N_PEM_DELIMTER_CHAR, S2N_PEM_DELIMITER_MIN_COUNT,
+    /* Ensure between 2 and 64 '-' chars at end of line */
+    POSIX_GUARD(s2n_stuffer_skip_expected_char(pem, S2N_PEM_DELIMITER_CHAR, S2N_PEM_DELIMITER_MIN_COUNT,
             S2N_PEM_DELIMITER_MAX_COUNT, NULL));
 
     /* Check for missing newline between dashes case: "-----END CERTIFICATE----------BEGIN CERTIFICATE-----" */
@@ -60,7 +66,7 @@ static int s2n_stuffer_pem_read_encapsulation_line(struct s2n_stuffer *pem, cons
         POSIX_GUARD(s2n_stuffer_rewind_read(pem, 1));
     }
 
-    /* Skip newlines and other whitepsace that may be after the dashes */
+    /* Skip newlines and other whitespace that may be after the dashes */
     return s2n_stuffer_skip_whitespace(pem, NULL);
 }