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[v2] merge-ort: fix calling merge_finalize() with no intermediate merge

Message ID pull.1518.v2.git.1682194930766.gitgitgadget@gmail.com (mailing list archive)
State Accepted
Commit 000c4ceca794645eb4744f9c9afb6247232c0646
Headers show
Series [v2] merge-ort: fix calling merge_finalize() with no intermediate merge | expand

Commit Message

Elijah Newren April 22, 2023, 8:22 p.m. UTC 
From: Elijah Newren <newren@gmail.com>

If some code sets up the data structures for a merge, but then never
actually performs one before calling merge_finalize(), then
merge_finalize() wouldn't notice that result->priv was NULL and
return early, resulting in following that NULL pointer and getting
a segfault.  There is currently no code in the git codebase that does
this, but this issue was found during testing of some proposed patches
that had the following structure:

    struct merge_options merge_opt;
    struct merge_result result;

    init_merge_options(&merge_opt, the_repository);
    memset(&result, 0, sizeof(result));

    <do N merges, for some value of N>

    merge_finalize(&merge_opt, &result);

where some flags could cause the code to have N=0, i.e. doing no merges.
Add a check for result->priv being NULL and return early to avoid a
segfault in these kinds of cases.

While at it, ensure the FREE_AND_NULL() in the function does something
useful with the nulling aspect, namely sets result->priv to NULL rather
than a mere temporary.

Reported-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
---
    merge-ort: fix calling merge_finalize() with no intermediate merge
    
    Changes since v1:
    
     * Moved code into an if-block instead of returning early, as suggested
       by Stolee.
    
    See
    https://lore.kernel.org/git/CABPp-BHCdjOutYqdMO1NbYKNA0BgkXRgwUEKK=MX0kXM-5G_DQ@mail.gmail.com/

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1518%2Fnewren%2Ffix-merge-finalize-with-no-merge-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1518/newren/fix-merge-finalize-with-no-merge-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/1518

Range-diff vs v1:

 1:  e636027f60c ! 1:  2cb1c63f05b merge-ort: fix calling merge_finalize() with no intermediate merge
     @@ merge-ort.c: void merge_switch_to_result(struct merge_options *opt,
       
      -	clear_or_reinit_internal_opts(opti, 0);
      -	FREE_AND_NULL(opti);
     -+	if (!result->priv)
     -+		return;
     -+	clear_or_reinit_internal_opts(result->priv, 0);
     -+	FREE_AND_NULL(result->priv);
     ++	if (result->priv) {
     ++		clear_or_reinit_internal_opts(result->priv, 0);
     ++		FREE_AND_NULL(result->priv);
     ++	}
       }
       
       /*** Function Grouping: helper functions for merge_incore_*() ***/


 merge-ort.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)


base-commit: 667fcf4e15379790f0b609d6a83d578e69f20301

Comments

Derrick Stolee April 24, 2023, 3:17 p.m. UTC | #1 
On 4/22/2023 4:22 PM, Elijah Newren via GitGitGadget wrote:
>     merge-ort: fix calling merge_finalize() with no intermediate merge
>     
>     Changes since v1:
>     
>      * Moved code into an if-block instead of returning early, as suggested
>        by Stolee.

v2 LGTM. Thanks!

-Stolee
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Patch

diff --git a/merge-ort.c b/merge-ort.c
index 5bf64354d16..29966fc082f 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -4718,14 +4718,14 @@  void merge_switch_to_result(struct merge_options *opt,
 void merge_finalize(struct merge_options *opt,
 		    struct merge_result *result)
 {
-	struct merge_options_internal *opti = result->priv;
-
 	if (opt->renormalize)
 		git_attr_set_direction(GIT_ATTR_CHECKIN);
 	assert(opt->priv == NULL);
 
-	clear_or_reinit_internal_opts(opti, 0);
-	FREE_AND_NULL(opti);
+	if (result->priv) {
+		clear_or_reinit_internal_opts(result->priv, 0);
+		FREE_AND_NULL(result->priv);
+	}
 }
 
 /*** Function Grouping: helper functions for merge_incore_*() ***/