[PATCH v3 09/13] merge-ort: avoid accidental API mis-use
- From
Elijah Newren via GitGitGadget <gitgitgadget@gmail.com>
- Date
- May 20, 2021, 06:09 UTC
- Message-ID
- <441e66fb2d19af6330def8f233bc3776f6da4797.1621490982.git.gitgitgadget@gmail.com>
- In-Reply-To
- <pull.859.v3.git.1621490982.gitgitgadget@gmail.com>
From: Elijah Newren <newren@gmail.com>
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> --- merge-ort.c | 7 +++++++ merge-ort.h | 2 ++ 2 files changed, 9 insertions(+)
diff --git a/merge-ort.c b/merge-ort.c index e08b60a26d20..6d2b53a4943f 100644 --- a/merge-ort.c +++ b/merge-ort.c @@ -53,6 +53,8 @@ enum merge_side { MERGE_SIDE2 = 2 }; +static unsigned RESULT_INITIALIZED = 0x1abe11ed; /* unlikely accidental value */ + struct traversal_callback_data { unsigned long mask; unsigned long dirmask; @@ -3760,6 +3762,10 @@ 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; @@ -3919,6 +3925,7 @@ 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; } } diff --git a/merge-ort.h b/merge-ort.h index d53a0a339f33..c011864ffeb1 100644 --- a/merge-ort.h +++ b/merge-ort.h @@ -29,6 +29,8 @@ struct merge_result { * !clean) and to print "CONFLICT" messages. Not for external use. */ void *priv; + /* Also private */ + unsigned _properly_initialized; }; /*
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