[CritFix] Fix mime encoding logic

diff --git a/src/libmime/mime_headers.c b/src/libmime/mime_headers.c
index 63419d6a399791c51310f6c6b3bd530e0054a30b..89be819eb926c7e0bd99c84447addaa8e6f6a049 100644 (file)
--- a/src/libmime/mime_headers.c
+++ b/src/libmime/mime_headers.c
@@ -831,70 +831,93 @@ rspamd_mime_header_encode(const char *in, gsize len, bool is_structured)
                        p++;
                }
                else {
-                       const char *q = end;
-                       size_t piece_len = q - p, encoded_len = 0;
-
-                       /* Check if the piece contains non-ASCII characters */
+                       const char *piece_end = end;
+                       size_t piece_len = piece_end - p;
                        gboolean need_encoding = FALSE;
-                       size_t unencoded_prefix = 0, unencoded_suffix = 0;
+                       size_t unencoded_prefix = 0;
+                       size_t encoded_len_count = 0;
+                       size_t enc_span = 0;
+
+                       /* Determine how much of this piece needs encoding and fits the budget */
                        for (size_t i = 0; i < piece_len; i++) {
                                unsigned char c = p[i];
-                               if (c >= 128 || (is_structured && !g_ascii_isalnum(c))) {
-                                       need_encoding = TRUE;
-                                       unencoded_suffix = 0;
-                                       encoded_len += 3;
 
-                                       if (encoded_len > max_token_size) {
-                                               piece_len = i;
-                                               q = p + piece_len;
-                                               /* No more space */
-                                               break;
+                               if (!need_encoding) {
+                                       if (c >= 128 || (is_structured && !g_ascii_isalnum(c))) {
+                                               need_encoding = TRUE;
+                                               /* Start encoded region with this char */
+                                               size_t add = (g_ascii_isalnum(c) || c == ' ') ? 1 : 3;
+
+                                               if (add > max_token_size) {
+                                                       /* Nothing fits, stop here to emit prefix only */
+                                                       piece_len = i;
+                                                       piece_end = p + piece_len;
+                                                       break;
+                                               }
+
+                                               encoded_len_count = add;
+                                               enc_span = 1;
+                                       }
+                                       else {
+                                               /* Still in unencoded prefix */
+                                               unencoded_prefix++;
                                        }
                                }
                                else {
-                                       encoded_len++;
-
-                                       if (encoded_len > max_token_size) {
+                                       /* Inside encoded part, stop on parentheses to keep them outside */
+                                       if (c == '(' || c == ')') {
                                                piece_len = i;
-                                               q = p + piece_len;
-                                               /* No more space */
+                                               piece_end = p + piece_len;
                                                break;
                                        }
 
-                                       if (need_encoding && (c == '(' || c == ')')) {
-                                               /* If we need to encode, we must stop on comments characters */
+                                       size_t add = (g_ascii_isalnum(c) || c == ' ') ? 1 : 3;
+
+                                       if (encoded_len_count + add > max_token_size) {
+                                               /* Budget exceeded; stop encoded span before this char */
                                                piece_len = i;
-                                               q = p + piece_len;
-                                               /* No more space */
+                                               piece_end = p + piece_len;
                                                break;
                                        }
 
-                                       if (!need_encoding) {
-                                               unencoded_prefix++;
-                                       }
-                                       else {
-                                               unencoded_suffix++;
-                                       }
+                                       encoded_len_count += add;
+                                       enc_span++;
                                }
                        }
 
-                       if (need_encoding) {
+                       if (need_encoding && enc_span > 0) {
+                               /* Emit prefix */
                                g_string_append_len(outbuf, p, unencoded_prefix);
                                p += unencoded_prefix;
+
+                               /* Encode encoded span safely within budget */
                                g_string_append(outbuf, "=?UTF-8?Q?");
-                               /* Do encode */
-                               encoded_len = rspamd_encode_qp2047_buf(p, piece_len - unencoded_prefix - unencoded_suffix,
-                                                                                                          encode_buf, max_token_size + 3);
-                               p += piece_len - unencoded_prefix - unencoded_suffix;
-                               g_string_append_len(outbuf, encode_buf, encoded_len);
-                               g_string_append(outbuf, "?=");
-                               g_string_append_len(outbuf, p, unencoded_suffix);
+
+                               gssize enc_written = rspamd_encode_qp2047_buf(p, enc_span,
+                                                                                                                         encode_buf, max_token_size);
+
+                               if (G_UNLIKELY(enc_written < 0)) {
+                                       /* Extremely conservative fallback: shrink until it fits */
+                                       while (enc_span > 0 && enc_written < 0) {
+                                               enc_span--;
+                                               enc_written = rspamd_encode_qp2047_buf(p, enc_span,
+                                                                                                                          encode_buf, max_token_size);
+                                       }
+                               }
+
+                               if (enc_span > 0 && enc_written >= 0) {
+                                       g_string_append_len(outbuf, encode_buf, (size_t) enc_written);
+                                       g_string_append(outbuf, "?=");
+                                       p += enc_span;
+                               }
+
+                               /* Do not append any suffix here; remaining bytes will be handled next loop */
                        }
                        else {
-                               /* No transformation */
+                               /* No encoding needed or nothing to encode */
                                g_string_append_len(outbuf, p, piece_len);
+                               p += piece_len;
                        }
-                       p = q;
                }
        }
 
@@ -1443,4 +1466,4 @@ gsize rspamd_strip_smtp_comments_inplace(char *input, gsize len)
        }
 
        return (d - start);
-}
\ No newline at end of file
+}