commit-graph.c: prevent overflow in `fill_commit_graph_info()`

In a similar spirit as previous commits, ensure that we don't overflow
in a few spots within `fill_commit_graph_info()`:

  - First, when computing an offset into the commit data chunk, which
    can occur when the `lex_index` of the item we're looking up exceeds
    2^32-1/GRAPH_DATA_WIDTH.

  - A similar issue when computing the generation date offset for
    commits with `lex_index` greater than 2^32-1/4. Note that in
    practice this will never overflow, since the left-hand operand is
    from calling `sizeof(...)` and is thus already a `size_t`. But wrap
    that in an `st_mult()` to make it clear that we intend to perform
    this computation using 64-bit operands.

  - Finally, a nearly identical issue as above when computing an offset
    into the `generation_data_overflow` chunk.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/commit-graph.c b/commit-graph.c
index 517c816a9450dda2f34e3a94a8a015d1f27a467c..69110e4dbb0c87ae6ea5cd4cd979be7f9532eafc 100644 (file)
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -790,7 +790,7 @@ static void fill_commit_graph_info(struct commit *item, struct commit_graph *g,
                die(_("invalid commit position. commit-graph is likely corrupt"));
 
        lex_index = pos - g->num_commits_in_base;
-       commit_data = g->chunk_commit_data + GRAPH_DATA_WIDTH * lex_index;
+       commit_data = g->chunk_commit_data + st_mult(GRAPH_DATA_WIDTH, lex_index);
 
        graph_data = commit_graph_data_at(item);
        graph_data->graph_pos = pos;
@@ -800,14 +800,14 @@ static void fill_commit_graph_info(struct commit *item, struct commit_graph *g,
        item->date = (timestamp_t)((date_high << 32) | date_low);
 
        if (g->read_generation_data) {
-               offset = (timestamp_t)get_be32(g->chunk_generation_data + sizeof(uint32_t) * lex_index);
+               offset = (timestamp_t)get_be32(g->chunk_generation_data + st_mult(sizeof(uint32_t), lex_index));
 
                if (offset & CORRECTED_COMMIT_DATE_OFFSET_OVERFLOW) {
                        if (!g->chunk_generation_data_overflow)
                                die(_("commit-graph requires overflow generation data but has none"));
 
                        offset_pos = offset ^ CORRECTED_COMMIT_DATE_OFFSET_OVERFLOW;
-                       graph_data->generation = item->date + get_be64(g->chunk_generation_data_overflow + 8 * offset_pos);
+                       graph_data->generation = item->date + get_be64(g->chunk_generation_data_overflow + st_mult(8, offset_pos));
                } else
                        graph_data->generation = item->date + offset;
        } else