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From: "SZEDER Gábor" <szeder.dev@gmail.com>
To: git@vger.kernel.org
Cc: "Junio C Hamano" <gitster@pobox.com>,
	"Garima Singh" <garima.singh@microsoft.com>,
	"Derrick Stolee" <stolee@gmail.com>,
	"Jakub Narebski" <jnareb@gmail.com>, "Jeff King" <peff@peff.net>,
	"Taylor Blau" <me@ttaylorr.com>,
	"SZEDER Gábor" <szeder.dev@gmail.com>
Subject: [PATCH 02/34] commit-graph: fix parsing the Chunk Lookup table
Date: Fri, 29 May 2020 10:50:06 +0200
Message-ID: <20200529085038.26008-3-szeder.dev@gmail.com> (raw)
In-Reply-To: <20200529085038.26008-1-szeder.dev@gmail.com>

The commit-graph file format specifies that the chunks may be in any
order.  However, if the OID Lookup chunk happens to be the last one in
the file, then any command attempting to access the commit-graph data
will fail with:

  fatal: invalid commit position. commit-graph is likely corrupt

In this case the error is wrong, the commit-graph file does conform to
the specification, but the parsing of the Chunk Lookup table is a bit
buggy, and leaves the field holding the number of commits in the
commit-graph zero-initialized.

The number of commits in the commit-graph is determined while parsing
the Chunk Lookup table, by dividing the size of the OID Lookup chunk
with the hash size.  However, the Chunk Lookup table doesn't actually
store the size of the chunks, but it stores their starting offset.
Consequently, the size of a chunk can only be calculated by
subtracting the starting offsets of that chunk from the offset of the
subsequent chunk, or in case of the last chunk from the offset
recorded in the terminating label.  This is currenly implemented in a
bit complicated way: as we iterate over the entries of the Chunk
Lookup table, we check the ID of each chunk and store its starting
offset, then we check the ID of the last seen chunk and calculate its
size using its previously saved offset if necessary (at the moment
it's only necessary for the OID Lookup chunk).  Alas, while parsing
the Chunk Lookup table we only interate through the "real" chunks, but
never look at the terminating label, thus don't even check whether
it's necessary to calulate the size of the last chunk.  Consequently,
if the OID Lookup chunk is the last one, then we don't calculate its
size and turn don't run the piece of code determining the number of
commits in the commit graph, leaving the field holding that number
unchanged (i.e. zero-initialized), eventually triggering the sanity
check in load_oid_from_graph().

Fix this by iterating through all entries in the Chunk Lookup table,
including the terminating label.

Note that this is the minimal fix, suitable for the maintenance track.
A better fix would be to simplify how the chunk sizes are calculated,
but that is a more invasive change, less suitable for 'maint', so that
will be done in later patches.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 commit-graph.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/commit-graph.c b/commit-graph.c
index b205e65ed1..12df74c925 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -222,7 +222,7 @@ struct commit_graph *parse_commit_graph(void *graph_map, int fd,
 	last_chunk_id = 0;
 	last_chunk_offset = 8;
 	chunk_lookup = data + 8;
-	for (i = 0; i < graph->num_chunks; i++) {
+	for (i = 0; i <= graph->num_chunks; i++) {
 		uint32_t chunk_id;
 		uint64_t chunk_offset;
 		int chunk_repeated = 0;
-- 
2.27.0.rc1.431.g5c813f95dc


  parent reply	other threads:[~2020-05-29  8:51 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-29  8:50 [PoC PATCH 00/34] An alternative modified path Bloom filters implementation SZEDER Gábor
2020-05-28 22:09 ` Johannes Schindelin
2020-05-29  8:50 ` [PATCH 01/34] tree-walk.c: don't match submodule entries for 'submod/anything' SZEDER Gábor
2020-05-29  8:50 ` SZEDER Gábor [this message]
2020-05-29  8:50 ` [PATCH 03/34] commit-graph-format.txt: all multi-byte numbers are in network byte order SZEDER Gábor
2020-05-29  8:50 ` [PATCH 04/34] commit-slab: add a function to deep free entries on the slab SZEDER Gábor
2020-06-04 16:43   ` Derrick Stolee
2020-06-27 15:56     ` SZEDER Gábor
2020-06-29 11:30       ` Derrick Stolee
2020-05-29  8:50 ` [PATCH 05/34] diff.h: drop diff_tree_oid() & friends' return value SZEDER Gábor
2020-05-29  8:50 ` [PATCH 06/34] commit-graph: clean up #includes SZEDER Gábor
2020-05-29  8:50 ` [PATCH 07/34] commit-graph: simplify parse_commit_graph() #1 SZEDER Gábor
2020-05-29  8:50 ` [PATCH 08/34] commit-graph: simplify parse_commit_graph() #2 SZEDER Gábor
2020-05-29  8:50 ` [PATCH 09/34] commit-graph: simplify write_commit_graph_file() #1 SZEDER Gábor
2020-05-29  8:50 ` [PATCH 10/34] commit-graph: simplify write_commit_graph_file() #2 SZEDER Gábor
2020-05-29  8:50 ` [PATCH 11/34] commit-graph: allocate the 'struct chunk_info' array dinamically SZEDER Gábor
2020-05-29  8:50 ` [PATCH 12/34] commit-graph: unify the signatures of all write_graph_chunk_*() functions SZEDER Gábor
2020-05-29  8:50 ` [PATCH 13/34] commit-graph: simplify write_commit_graph_file() #3 SZEDER Gábor
2020-05-29  8:50 ` [PATCH 14/34] commit-graph: check chunk sizes after writing SZEDER Gábor
2020-05-29  8:50 ` [PATCH 15/34] commit-graph-format.txt: document the modified path Bloom filter chunks SZEDER Gábor
2020-06-02 17:59   ` SZEDER Gábor
2020-05-29  8:50 ` [PATCH 16/34] Add a generic and minimal Bloom filter implementation SZEDER Gábor
2020-05-29  8:50 ` [PATCH 17/34] Import a streaming-capable Murmur3 hash function implementation SZEDER Gábor
2020-05-29  8:50 ` [PATCH 18/34] commit-graph: write "empty" Modified Path Bloom Filter Index chunk SZEDER Gábor
2020-05-29  8:50 ` [PATCH 19/34] commit-graph: add commit slab for modified path Bloom filters SZEDER Gábor
2020-05-29  8:50 ` [PATCH 20/34] commit-graph: fill the Modified Path Bloom Filter Index chunk SZEDER Gábor
2020-05-29  8:50 ` [PATCH 21/34] commit-graph: load and use " SZEDER Gábor
2020-05-29  8:50 ` [PATCH 22/34] commit-graph: write the Modified Path Bloom Filters chunk SZEDER Gábor
2020-05-29  8:50 ` [PATCH 23/34] commit-graph: load and use " SZEDER Gábor
2020-05-29  8:50 ` [PATCH 24/34] commit-graph: check all leading directories in modified path Bloom filters SZEDER Gábor
2020-05-29  8:50 ` [PATCH 25/34] commit-graph: check embedded modified path Bloom filters with a mask SZEDER Gábor
2020-05-29  8:50 ` [PATCH 26/34] commit-graph: deduplicate modified path Bloom filters SZEDER Gábor
2020-05-29  8:50 ` [PATCH 27/34] commit-graph: load modified path Bloom filters for merge commits SZEDER Gábor
2020-05-29  8:50 ` [PATCH 28/34] commit-graph: write Modified Path Bloom Filter Merge Index chunk SZEDER Gábor
2020-05-29  8:50 ` [PATCH 29/34] commit-graph: extract init and free write_commit_graph_context SZEDER Gábor
2020-05-29  8:50 ` [PATCH 30/34] commit-graph: move write_commit_graph_reachable below write_commit_graph SZEDER Gábor
2020-05-29  8:50 ` [PATCH 31/34] t7007-show: make the first test compatible with the next patch SZEDER Gábor
2020-05-29  8:50 ` [PATCH 32/34] PoC commit-graph: use revision walk machinery for '--reachable' SZEDER Gábor
2020-05-29  8:50 ` [PATCH 33/34] commit-graph: write modified path Bloom filters in "history order" SZEDER Gábor
2020-05-29  8:50 ` [PATCH 34/34] commit-graph: use modified path Bloom filters with wildcards, if possible SZEDER Gábor
2020-05-29 13:59 ` [PoC PATCH 00/34] An alternative modified path Bloom filters implementation Derrick Stolee
2020-06-01 23:25 ` Taylor Blau
2020-06-02 17:08   ` Junio C Hamano

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