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traverse_trees(): use stack array for name entries

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We heap-allocate our arrays of name_entry structs, etc, with one entry
per tree we're asked to traverse. The code does a raw multiplication in
the xmalloc() call, which I find when auditing for integer overflows
during allocation.

We could "fix" this by using ALLOC_ARRAY() instead. But as it turns out,
the maximum size of these arrays is limited at compile time:

  - merge_trees() always passes in 3 trees

  - unpack_trees() and its brethren never pass in more than
    MAX_UNPACK_TREES

So we can simplify even further by just using a stack array and bounding
it with MAX_UNPACK_TREES. There should be no concern with overflowing
the stack, since MAX_UNPACK_TREES is only 8 and the structs themselves
are small.

Note that since we're replacing xcalloc(), we have to move one of the
NULL initializations into a loop.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2020-01-30 04:53:38 -05:00 committed by Junio C Hamano
parent 667b76ec58
commit 8dd40c0472
1 changed files with 8 additions and 5 deletions
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13
tree-walk.c
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@ -410,15 +410,20 @@ int traverse_trees(struct index_state *istate,
struct traverse_info *info)
{
int error = 0;
struct name_entry *entry = xmalloc(n*sizeof(*entry));
struct name_entry entry[MAX_UNPACK_TREES];
int i;
struct tree_desc_x *tx = xcalloc(n, sizeof(*tx));
struct tree_desc_x tx[ARRAY_SIZE(entry)];
struct strbuf base = STRBUF_INIT;
int interesting = 1;
char *traverse_path;
for (i = 0; i < n; i++)
if (n >= ARRAY_SIZE(entry))
BUG("traverse_trees() called with too many trees (%d)", n);
for (i = 0; i < n; i++) {
tx[i].d = t[i];
tx[i].skip = NULL;
}
if (info->prev) {
strbuf_make_traverse_path(&base, info->prev,
@ -506,10 +511,8 @@ int traverse_trees(struct index_state *istate,
if (mask & (1ul << i))
update_extended_entry(tx + i, entry + i);
}
free(entry);
for (i = 0; i < n; i++)
free_extended_entry(tx + i);
free(tx);
free(traverse_path);
info->traverse_path = NULL;
strbuf_release(&base);