Apply similar treatment as in the previous commit to handle an unchecked
call to 'get_commit_tree_oid()'. Previously, a NULL return value from
this function would be immediately dereferenced with '->hash', and then
cause a segfault.

Before dereferencing to access the 'hash' member, check the return value
of 'get_commit_tree_oid()' to make sure that it is not NULL.

To make this check correct, a related change is also needed in
'commit.c', which is to check the return value of 'get_commit_tree'
before taking its address. If 'get_commit_tree' returns NULL, we
encounter an undefined behavior when taking the address of the return
value of 'get_commit_tree' and then taking '->object.oid'. (On my system,
this is memory address 0x8, which is obviously wrong).

Fix this by making sure that 'get_commit_tree' returns something
non-NULL before digging through a structure that is not there, thus
preventing a segfault down the line in the commit graph code.

Signed-off-by: Taylor Blau <>
 commit-graph.c          | 7 ++++++-
 commit.c                | 3 ++-
 t/ | 2 +-
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/commit-graph.c b/commit-graph.c
index 6aa6998ecd..cea1b37493 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -839,6 +839,7 @@ static void write_graph_chunk_data(struct hashfile *f, int 
        while (list < last) {
                struct commit_list *parent;
+               struct object_id *tree;
                int edge_value;
                uint32_t packedDate[2];
                display_progress(ctx->progress, ++ctx->progress_cnt);
@@ -846,7 +847,11 @@ static void write_graph_chunk_data(struct hashfile *f, int 
                if (parse_commit_no_graph(*list))
                        die(_("unable to parse commit %s"),
-               hashwrite(f, get_commit_tree_oid(*list)->hash, hash_len);
+               tree = get_commit_tree_oid(*list);
+               if (!tree)
+                       die(_("unable to get tree for %s"),
+                               oid_to_hex(&(*list)->object.oid));
+               hashwrite(f, tree->hash, hash_len);
                parent = (*list)->parents;
diff --git a/commit.c b/commit.c
index a98de16e3d..fab22cb740 100644
--- a/commit.c
+++ b/commit.c
@@ -358,7 +358,8 @@ struct tree *repo_get_commit_tree(struct repository *r,
 struct object_id *get_commit_tree_oid(const struct commit *commit)
-       return &get_commit_tree(commit)->object.oid;
+       struct tree *tree = get_commit_tree(commit);
+       return tree ? &tree->object.oid : NULL;
 void release_commit_memory(struct parsed_object_pool *pool, struct commit *c)
diff --git a/t/ b/t/
index abde8d4e90..5d2d88b100 100755
--- a/t/
+++ b/t/
@@ -607,7 +607,7 @@ test_expect_success 'corrupt commit-graph write (broken 
parent)' '
-test_expect_failure 'corrupt commit-graph write (missing tree)' '
+test_expect_success 'corrupt commit-graph write (missing tree)' '
        rm -rf repo &&
        git init repo &&

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