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[PATCH 05/20] midx.c: prevent overflow in `nth_midxed_object_oid()`

From
Taylor Blau <me@ttaylorr.com>
Date
Jul 12, 2023, 23:37 UTC
Message-ID
<1a60b79296c567da33cb8e7001ff21c484836989.1689205042.git.me@ttaylorr.com>
In-Reply-To
<cover.1689205042.git.me@ttaylorr.com>

In a similar spirit as previous commits, avoid overflow when looking up an object's OID in a MIDX when its position is greater than `2^32-1/m->hash_len`.

As usual, it is perfectly OK for a MIDX to have as many as 2^32-1 objects (since we use 32-bit fields to count the number of objects at each fanout layer). But if we have more than `2^32-1/m->hash_len` number of objects, we will incorrectly perform the computation using 32-bit integers, overflowing the result.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
 midx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/midx.c b/midx.c
index 449c10289c..dbc63c0d42 100644
--- a/midx.c
+++ b/midx.c
@@ -254,7 +254,7 @@ struct object_id *nth_midxed_object_oid(struct object_id *oid,
 	if (n >= m->num_objects)
 		return NULL;
 
-	oidread(oid, m->chunk_oid_lookup + m->hash_len * n);
+	oidread(oid, m->chunk_oid_lookup + st_mult(m->hash_len, n));
 	return oid;
 }
 

-- 
2.41.0.347.g7b976b8871f
Previous: Taylor BlauNext: Taylor Blau
Message 13 of 28 in “guard object lookups against 32-bit overflow”
  1. 00/20 guard object lookups against 32-bit overflowTaylor Blau, Jul 12, 2023
  2. 01/20 packfile.c: prevent overflow in `nth_packed_object_id()`Taylor Blau, Jul 12, 2023
  3. 02/20 packfile.c: prevent overflow in `load_idx()`Taylor Blau, Jul 12, 2023
  4. Phillip WoodJul 13, 2023
  5. Taylor BlauJul 13, 2023
  6. Taylor BlauJul 14, 2023
  7. Phillip WoodJul 14, 2023
  8. Junio C HamanoJul 14, 2023
  9. Phillip WoodJul 14, 2023
  10. Junio C HamanoJul 13, 2023
  11. 03/20 packfile.c: use checked arithmetic in `nth_packed_object_offset()`Taylor Blau, Jul 12, 2023
  12. 04/20 midx.c: use `size_t`'s for fanout nr and allocTaylor Blau, Jul 12, 2023
  13. 05/20 midx.c: prevent overflow in `nth_midxed_object_oid()`Taylor Blau, Jul 12, 2023
  14. 06/20 midx.c: prevent overflow in `nth_midxed_offset()`Taylor Blau, Jul 12, 2023
  15. 08/20 midx.c: prevent overflow in `write_midx_internal()`Taylor Blau, Jul 12, 2023
  16. 09/20 midx.c: prevent overflow in `fill_included_packs_batch()`Taylor Blau, Jul 12, 2023
  17. 10/20 pack-bitmap.c: ensure that eindex lookups don't overflowTaylor Blau, Jul 12, 2023
  18. 11/20 commit-graph.c: prevent overflow in `write_commit_graph_file()`Taylor Blau, Jul 12, 2023
  19. 12/20 commit-graph.c: prevent overflow in add_graph_to_chain()Taylor Blau, Jul 12, 2023
  20. 13/20 commit-graph.c: prevent overflow in `load_oid_from_graph()`Taylor Blau, Jul 12, 2023
  21. 14/20 commit-graph.c: prevent overflow in `fill_commit_graph_info()`Taylor Blau, Jul 12, 2023
  22. 15/20 commit-graph.c: prevent overflow in `fill_commit_in_graph()`Taylor Blau, Jul 12, 2023
  23. 16/20 commit-graph.c: prevent overflow in `load_tree_for_commit()`Taylor Blau, Jul 12, 2023
  24. 17/20 commit-graph.c: prevent overflow in `split_graph_merge_strategy()`Taylor Blau, Jul 12, 2023
  25. 18/20 commit-graph.c: prevent overflow in `merge_commit_graph()`Taylor Blau, Jul 12, 2023
  26. 19/20 commit-graph.c: prevent overflow in `write_commit_graph()`Taylor Blau, Jul 12, 2023
  27. 20/20 commit-graph.c: prevent overflow in `verify_commit_graph()`Taylor Blau, Jul 12, 2023
  28. 07/20 midx.c: store `nr`, `alloc` variables as `size_t`'sTaylor Blau, Jul 12, 2023

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