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[tor-commits] [tor/master] bug#22143/prop#140: Use <n>, $d commands in diffs to remove signatures



commit c8baa9b78362e372cfb5e2d3fcc6100d20d00229
Author: Nick Mathewson <nickm@xxxxxxxxxxxxxx>
Date:   Wed May 3 12:34:30 2017 -0400

    bug#22143/prop#140: Use <n>,$d commands in diffs to remove signatures
    
    In this patch I add support for "delete through end of file" in our
    ed diff handler, and generate our diffs so that they remove
    everything after in the consensus after the signatures begin.
---
 src/or/consdiff.c        | 91 ++++++++++++++++++++++++++++++++++++++++++++----
 src/test/test_consdiff.c | 18 ++++++----
 2 files changed, 96 insertions(+), 13 deletions(-)

diff --git a/src/or/consdiff.c b/src/or/consdiff.c
index e4f7872..3c2140b 100644
--- a/src/or/consdiff.c
+++ b/src/or/consdiff.c
@@ -65,17 +65,35 @@ line_str_eq(const cdline_t *a, const char *b)
   return lines_eq(a, &bline);
 }
 
-/** Add a cdline_t to <b>lst</b> holding as its contents the nul-terminated
- * string s.  Use the provided memory area for storage. */
-STATIC void
-smartlist_add_linecpy(smartlist_t *lst, memarea_t *area, const char *s)
+/** Return true iff a begins with the same contents as the nul-terminated
+ * string b. */
+static int
+line_starts_with_str(const cdline_t *a, const char *b)
+{
+  const size_t len = strlen(b);
+  tor_assert(len <= UINT32_MAX);
+  return a->len >= len && fast_memeq(a->s, b, len);
+}
+
+/** Return a new cdline_t holding as its contents the nul-terminated
+ * string s. Use the provided memory area for storage. */
+static cdline_t *
+cdline_linecpy(memarea_t *area, const char *s)
 {
   size_t len = strlen(s);
   const char *ss = memarea_memdup(area, s, len);
   cdline_t *line = memarea_alloc(area, sizeof(cdline_t));
   line->s = ss;
   line->len = (uint32_t)len;
-  smartlist_add(lst, line);
+  return line;
+}
+
+/** Add a cdline_t to <b>lst</b> holding as its contents the nul-terminated
+ * string s.  Use the provided memory area for storage. */
+STATIC void
+smartlist_add_linecpy(smartlist_t *lst, memarea_t *area, const char *s)
+{
+  smartlist_add(lst, cdline_linecpy(area, s));
 }
 
 /** Compute the digest of <b>cons</b>, and store the result in
@@ -545,6 +563,42 @@ find_next_router_line(const smartlist_t *cons,
   return 0;
 }
 
+/** Line-prefix indicating the beginning of the signatures section that we
+ * intend to delete. */
+#define START_OF_SIGNATURES_SECTION "directory-signature "
+
+/** Pre-process a consensus in <b>cons</b> (represented as a list of cdline_t)
+ * to remove the signatures from it.  If the footer is removed, return a
+ * cdline_t containing a delete command to delete the footer, allocated in
+ * <b>area</>.  If no footer is removed, return NULL.
+ *
+ * We remove the signatures here because they are not themselves signed, and
+ * as such there might be different encodings for them.
+ */
+static cdline_t *
+preprocess_consensus(memarea_t *area,
+                     smartlist_t *cons)
+{
+  int idx;
+  int dirsig_idx = -1;
+  for (idx = 0; idx < smartlist_len(cons); ++idx) {
+    cdline_t *line = smartlist_get(cons, idx);
+    if (line_starts_with_str(line, START_OF_SIGNATURES_SECTION)) {
+      dirsig_idx = idx;
+      break;
+    }
+  }
+  if (dirsig_idx >= 0) {
+    char buf[64];
+    while (smartlist_len(cons) > dirsig_idx)
+      smartlist_del(cons, dirsig_idx);
+    tor_snprintf(buf, sizeof(buf), "%d,$d", dirsig_idx+1);
+    return cdline_linecpy(area, buf);
+  } else {
+    return NULL;
+  }
+}
+
 /** Generate an ed diff as a smartlist from two consensuses, also given as
  * smartlists. Will return NULL if the diff could not be generated, which can
  * happen if any lines the script had to add matched "." or if the routers
@@ -566,13 +620,22 @@ find_next_router_line(const smartlist_t *cons,
  *   calc_changes(cons1_sl, cons2_sl, changed1, changed2);
  */
 STATIC smartlist_t *
-gen_ed_diff(const smartlist_t *cons1, const smartlist_t *cons2,
+gen_ed_diff(const smartlist_t *cons1_orig, const smartlist_t *cons2,
             memarea_t *area)
 {
+  smartlist_t *cons1 = smartlist_new();
+  smartlist_add_all(cons1, cons1_orig);
+  cdline_t *remove_trailer = preprocess_consensus(area, cons1);
+
   int len1 = smartlist_len(cons1);
   int len2 = smartlist_len(cons2);
   smartlist_t *result = smartlist_new();
 
+  if (remove_trailer) {
+    /* There's a delete-the-trailer line at the end, so add it here. */
+    smartlist_add(result, remove_trailer);
+  }
+
   /* Initialize the changed bitarrays to zero, so that calc_changes only needs
    * to set the ones that matter and leave the rest untouched.
    */
@@ -746,6 +809,7 @@ gen_ed_diff(const smartlist_t *cons1, const smartlist_t *cons2,
     }
   }
 
+  smartlist_free(cons1);
   bitarray_free(changed1);
   bitarray_free(changed2);
 
@@ -753,6 +817,7 @@ gen_ed_diff(const smartlist_t *cons1, const smartlist_t *cons2,
 
  error_cleanup:
 
+  smartlist_free(cons1);
   bitarray_free(changed1);
   bitarray_free(changed2);
 
@@ -811,6 +876,7 @@ apply_ed_diff(const smartlist_t *cons1, const smartlist_t *diff,
     const char *ptr = diff_line;
     int start = 0, end = 0;
     int had_range = 0;
+    int end_was_eof = 0;
     if (get_linenum(&ptr, &start) < 0) {
       log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
                "an ed command was missing a line number.");
@@ -820,7 +886,11 @@ apply_ed_diff(const smartlist_t *cons1, const smartlist_t *diff,
       /* Two-item range */
       had_range = 1;
       ++ptr;
-      if (get_linenum(&ptr, &end) < 0) {
+      if (*ptr == '$') {
+        end_was_eof = 1;
+        end = smartlist_len(cons1);
+        ++ptr;
+      } else if (get_linenum(&ptr, &end) < 0) {
         log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
                  "an ed command was missing a range end line number.");
         goto error_cleanup;
@@ -867,6 +937,13 @@ apply_ed_diff(const smartlist_t *cons1, const smartlist_t *diff,
         goto error_cleanup;
     }
 
+    /** $ is not allowed with non-d actions. */
+    if (end_was_eof && action != 'd') {
+      log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
+               "it wanted to use $ with a command other than delete");
+      goto error_cleanup;
+    }
+
     /* 'a' commands are not allowed to have ranges. */
     if (had_range && action == 'a') {
       log_warn(LD_CONSDIFF, "Could not apply consensus diff because "
diff --git a/src/test/test_consdiff.c b/src/test/test_consdiff.c
index 2e78672..cdc1e6d 100644
--- a/src/test/test_consdiff.c
+++ b/src/test/test_consdiff.c
@@ -931,18 +931,24 @@ test_consdiff_gen_diff(void *arg)
   consensus_split_lines(cons1, cons1_str, area);
   diff = consdiff_gen_diff(cons1, cons2, &digests1, &digests2, area);
   tt_ptr_op(NULL, OP_NE, diff);
-  tt_int_op(7, OP_EQ, smartlist_len(diff));
+  tt_int_op(11, OP_EQ, smartlist_len(diff));
   tt_assert(line_str_eq(smartlist_get(diff, 0),
                         "network-status-diff-version 1"));
   tt_assert(line_str_eq(smartlist_get(diff, 1), "hash "
       "95D70F5A3CC65F920AA8B44C4563D7781A082674329661884E19E94B79D539C2 "
       "7AFECEFA4599BA33D603653E3D2368F648DF4AC4723929B0F7CF39281596B0C1"));
-  tt_assert(line_str_eq(smartlist_get(diff, 2), "3,4d"));
-  tt_assert(line_str_eq(smartlist_get(diff, 3), "1a"));
-  tt_assert(line_str_eq(smartlist_get(diff, 4),
+  tt_assert(line_str_eq(smartlist_get(diff, 2), "6,$d"));
+  tt_assert(line_str_eq(smartlist_get(diff, 3), "3,4c"));
+  tt_assert(line_str_eq(smartlist_get(diff, 4), "bar"));
+  tt_assert(line_str_eq(smartlist_get(diff, 5),
+                        "directory-signature foo bar"));
+  tt_assert(line_str_eq(smartlist_get(diff, 6),
+                        "."));
+  tt_assert(line_str_eq(smartlist_get(diff, 7), "1a"));
+  tt_assert(line_str_eq(smartlist_get(diff, 8),
                         "r name aaaaaaaaaaaaaaaaa etc"));
-  tt_assert(line_str_eq(smartlist_get(diff, 5), "foo"));
-  tt_assert(line_str_eq(smartlist_get(diff, 6), "."));
+  tt_assert(line_str_eq(smartlist_get(diff, 9), "foo"));
+  tt_assert(line_str_eq(smartlist_get(diff, 10), "."));
 
   /* TODO: small real use-cases, i.e. consensuses. */
 



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