| Message ID | pull.1518.git.1681974847078.gitgitgadget@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | merge-ort: fix calling merge_finalize() with no intermediate merge | expand |
On 4/20/2023 3:14 AM, Elijah Newren via GitGitGadget wrote: > From: Elijah Newren <newren@gmail.com> > 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. Good call. It also makes the code look better. > 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); Perhaps this would be better as if (result->priv) { clear_or_reinit_internal_opts(result->priv, 0); FREE_AND_NULL(result->priv); } to avoid an accidental addition of code to the end of this method that doesn't depend on result->priv? Thanks, -Stolee
"Elijah Newren via GitGitGadget" <gitgitgadget@gmail.com> writes: > 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. 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@github.com> > Signed-off-by: Elijah Newren <newren@gmail.com> > --- > merge-ort: fix calling merge_finalize() with no intermediate merge > > 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-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
Derrick Stolee <derrickstolee@github.com> writes: > On 4/20/2023 3:14 AM, Elijah Newren via GitGitGadget wrote: >> From: Elijah Newren <newren@gmail.com> > >> 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. > > Good call. It also makes the code look better. And more correct, if the NULLness of result->priv matters. > Perhaps this would be better as > > if (result->priv) { > clear_or_reinit_internal_opts(result->priv, 0); > FREE_AND_NULL(result->priv); > } > > to avoid an accidental addition of code to the end of this > method that doesn't depend on result->priv? It does sound like a good idea. Thanks.
On Thu, Apr 20, 2023 at 6:10 AM Derrick Stolee <derrickstolee@github.com> wrote: > > On 4/20/2023 3:14 AM, Elijah Newren via GitGitGadget wrote: > > From: Elijah Newren <newren@gmail.com> > > > 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. > > Good call. It also makes the code look better. > > > 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); > > Perhaps this would be better as > > if (result->priv) { > clear_or_reinit_internal_opts(result->priv, 0); > FREE_AND_NULL(result->priv); > } > > to avoid an accidental addition of code to the end of this > method that doesn't depend on result->priv? Ooh, yes, that'd be a good improvement; thanks.
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_*() ***/