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merge-ort: avoid accidental API mis-use 

Previously, callers of the merge-ort API could have passed an
uninitialized value for struct merge_result *result.  However, we want
to check result to see if it has cached renames from a previous merge
that we can reuse; such values would be found behind result->priv.
However, if result->priv is uninitialized, attempting to access behind
it will give a segfault.  So, we need result->priv to be NULL (which
will be the case if the caller does a memset(&result, 0)), or be written
by a previous call to the merge-ort machinery.  Documenting this
requirement may help, but despite being the person who introduced this
requirement, I still missed it once and it did not fail in a very clear
way and led to a long debugging session.

Add a _properly_initialized field to merge_result; that value will be
0 if the caller zero'ed the merge_result, it will be set to a very
specific value by a previous run by the merge-ort machinery, and if it's
uninitialized it will most likely either be 0 or some value that does
not match the specific one we'd expect allowing us to throw a much more
meaningful error.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Elijah Newren 2021-05-20 06:09:37 +00:00 committed by Junio C Hamano
parent 64aceb6d73
commit 19ceb486f8
2 changed files with 9 additions and 0 deletions
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7
merge-ort.c
View File

@ -52,6 +52,8 @@ enum merge_side {
MERGE_SIDE2 = 2
};
static unsigned RESULT_INITIALIZED = 0x1abe11ed; /* unlikely accidental value */
struct traversal_callback_data {
unsigned long mask;
unsigned long dirmask;
@ -3768,6 +3770,10 @@ static void merge_start(struct merge_options *opt, struct merge_result *result)
assert(opt->obuf.len == 0);
assert(opt->priv == NULL);
if (result->_properly_initialized != 0 &&
result->_properly_initialized != RESULT_INITIALIZED)
BUG("struct merge_result passed to merge_incore_*recursive() must be zeroed or filled with values from a previous run");
assert(!!result->priv == !!result->_properly_initialized);
if (result->priv) {
opt->priv = result->priv;
result->priv = NULL;
@ -3927,6 +3933,7 @@ static void merge_ort_nonrecursive_internal(struct merge_options *opt,
result->clean &= strmap_empty(&opt->priv->conflicted);
if (!opt->priv->call_depth) {
result->priv = opt->priv;
result->_properly_initialized = RESULT_INITIALIZED;
opt->priv = NULL;
}
}

2
merge-ort.h
View File

@ -29,6 +29,8 @@ struct merge_result {
* !clean) and to print "CONFLICT" messages. Not for external use.
*/
void *priv;
/* Also private */
unsigned _properly_initialized;
};
/*