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commit-graph.c: handle corrupt/missing trees

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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 <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Taylor Blau
2019-09-05 18:04:57 -04:00
committed by Junio C Hamano
parent 16749b8dd2
commit 806278dead
3 changed files with 9 additions and 3 deletions
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7
commit-graph.c
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@ -839,6 +839,7 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
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 hash_len,
if (parse_commit_no_graph(*list))
die(_("unable to parse commit %s"),
oid_to_hex(&(*list)->object.oid));
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;