"Elijah Newren via GitGitGadget" <gitgitgadget@xxxxxxxxx> writes: > From: Elijah Newren <newren@xxxxxxxxx> > > 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. Clearly written. The FREE_AND_NULL() bit is a bit embarrassing slip-up for everybody who reviewed and applied the initial patch X-<. And we need to undo the attribute direction change in merge_start() even if we didn't perform any, so the early return cannot be done before that. So everything makes sense as a fix to the reported problem. > Reported-by: Derrick Stolee <derrickstolee@xxxxxxxxxx> > Signed-off-by: Elijah Newren <newren@xxxxxxxxx> > --- > merge-ort: fix calling merge_finalize() with no intermediate merge > > See > https://lore.kernel.org/git/CABPp-BHCdjOutYqdMO1NbYKNA0BgkXRgwUEKK=MX0kXM-5G_DQ@xxxxxxxxxxxxxx/ > > Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1518%2Fnewren%2Ffix-merge-finalize-with-no-merge-v1 > Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1518/newren/fix-merge-finalize-with-no-merge-v1 > Pull-Request: https://github.com/gitgitgadget/git/pull/1518 > > merge-ort.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/merge-ort.c b/merge-ort.c > index 5bf64354d16..cba3662e497 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) > + return; > + clear_or_reinit_internal_opts(result->priv, 0); > + FREE_AND_NULL(result->priv); > } > > /*** Function Grouping: helper functions for merge_incore_*() ***/ > > base-commit: 667fcf4e15379790f0b609d6a83d578e69f20301
