# [PATCH] fix null pointer dereference 4 messages from 2021-03-21 to 2021-03-21. Participants: Kleber Tarcísio via GitGitGadget, Ævar Arnfjörð Bjarmason, Matheus Tavares Bernardino, Junio C Hamano. Thread: https://gitlist.dev/t/55360 ## Kleber Tarcísio via GitGitGadget, 2021-03-21 10:52 Subject: [PATCH] fix null pointer dereference Message-ID: URL: https://gitlist.dev/e/pull.983.git.git.1616323936790.gitgitgadget%40gmail.com ``` From: =?UTF-8?q?Kleber=20Tarc=C3=ADsio?= The malloc function can return null when the memory allocation fails. This commit adds a condition to handle these cases properly. https://cwe.mitre.org/data/definitions/476.html Signed-off-by: Kleber Tarcísio --- Avoiding null pointer dereference This pull request aims to fix null pointer dereference. Null pointer dereference [https://cwe.mitre.org/data/definitions/476.html] Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-983%2Fklebertarcisio%2Fpatch-1-v1 Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-983/klebertarcisio/patch-1-v1 Pull-Request: https://github.com/git/git/pull/983 builtin/submodule--helper.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c index 9d505a6329c8..92349d715a78 100644 --- a/builtin/submodule--helper.c +++ b/builtin/submodule--helper.c @@ -1215,6 +1215,8 @@ static void submodule_summary_callback(struct diff_queue_struct *q, if (!S_ISGITLINK(p->one->mode) && !S_ISGITLINK(p->two->mode)) continue; temp = (struct module_cb*)malloc(sizeof(struct module_cb)); + if (!temp) + die(_("out of memory")); temp->mod_src = p->one->mode; temp->mod_dst = p->two->mode; temp->oid_src = p->one->oid; base-commit: a5828ae6b52137b913b978e16cd2334482eb4c1f -- gitgitgadget ``` ## Ævar Arnfjörð Bjarmason, 2021-03-21 12:43 Subject: Re: [PATCH] fix null pointer dereference Message-ID: <87tup4r81k.fsf@evledraar.gmail.com> URL: https://gitlist.dev/e/87tup4r81k.fsf%40evledraar.gmail.com In-Reply-To: ``` On Sun, Mar 21 2021, Kleber Tarcísio via GitGitGadget wrote: > From: =?UTF-8?q?Kleber=20Tarc=C3=ADsio?= > > The malloc function can return null when the memory allocation fails. This commit adds a condition to handle these cases properly. https://cwe.mitre.org/data/definitions/476.html > > Signed-off-by: Kleber Tarcísio > --- > Avoiding null pointer dereference > > This pull request aims to fix null pointer dereference. > > Null pointer dereference > [https://cwe.mitre.org/data/definitions/476.html] > > Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-983%2Fklebertarcisio%2Fpatch-1-v1 > Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-983/klebertarcisio/patch-1-v1 > Pull-Request: https://github.com/git/git/pull/983 > > builtin/submodule--helper.c | 2 ++ > 1 file changed, 2 insertions(+) Thanks, from my brief grepping of the remaining code in git.git there is no other malloc() that doesn't have its return value checked appropriately. > diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c > index 9d505a6329c8..92349d715a78 100644 > --- a/builtin/submodule--helper.c > +++ b/builtin/submodule--helper.c > @@ -1215,6 +1215,8 @@ static void submodule_summary_callback(struct diff_queue_struct *q, > if (!S_ISGITLINK(p->one->mode) && !S_ISGITLINK(p->two->mode)) > continue; > temp = (struct module_cb*)malloc(sizeof(struct module_cb)); > + if (!temp) > + die(_("out of memory")); > temp->mod_src = p->one->mode; > temp->mod_dst = p->two->mode; > temp->oid_src = p->one->oid; When we just want to die if we can't allocate memory we should use the xmalloc() wrapper instead. ``` ## Matheus Tavares Bernardino, 2021-03-21 14:47 Subject: Re: [PATCH] fix null pointer dereference Message-ID: URL: https://gitlist.dev/e/CAHd-oW6hOQ5Qim1xMOJ23kjcpo1M-K1dDvzGKYjBCD9XoT2G%2BA%40mail.gmail.com In-Reply-To: ``` Hi, Kleber. And welcome to the list! On Sun, Mar 21, 2021 at 7:53 AM Kleber Tarcísio via GitGitGadget wrote: > > From: =?UTF-8?q?Kleber=20Tarc=C3=ADsio?= > > The malloc function can return null when the memory allocation fails. This commit adds a condition to handle these cases properly. https://cwe.mitre.org/data/definitions/476.html If you are going to re-roll this series, please wrap the commit message body at 72 columns. This helps viewing the message in 80-columns terminals. (For more info on this and other commit message conventions used by the Git project, please take a look at the corresponding sections at Documentation/MyFirstContribution.txt and Documentation/SubmittingPatches). Thanks, Matheus ``` ## Junio C Hamano, 2021-03-21 17:25 Subject: Re: [PATCH] fix null pointer dereference Message-ID: URL: https://gitlist.dev/e/xmqqft0oberu.fsf%40gitster.g In-Reply-To: ``` "Kleber Tarcísio via GitGitGadget" writes: > From: =?UTF-8?q?Kleber=20Tarc=C3=ADsio?= > Subject: Re: [PATCH] fix null pointer dereference Thanks, but see Documentation/SubmittingPatches for general guidelines. Our commit title begins with ":" so that when this change is buried among hundreds of other commits in "git shortlog --no-merges", the readers can tell what it is about. Subject: [PATCH] submodule-helper: avoid unchecked malloc() perhaps. > The malloc function can return null when the memory allocation fails. This commit adds a condition to handle these cases properly. https://cwe.mitre.org/data/definitions/476.html Overlong line. Also when you can say something without forcing readers to refer to external material, do so (and if you do not think you can, try harder ;-). In this case, I think you do not need to say anything more than submodule-helper.c::submodule_summary_callback() calls malloc() and uses the returned value without checking for NULLness. Use xmalloc() instaed. > diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c > index 9d505a6329c8..92349d715a78 100644 > --- a/builtin/submodule--helper.c > +++ b/builtin/submodule--helper.c > @@ -1215,6 +1215,8 @@ static void submodule_summary_callback(struct diff_queue_struct *q, > if (!S_ISGITLINK(p->one->mode) && !S_ISGITLINK(p->two->mode)) > continue; > temp = (struct module_cb*)malloc(sizeof(struct module_cb)); > + if (!temp) > + die(_("out of memory")); And this should be just - temp = (struct module_cb*)malloc(sizeof(struct module_cb)); + temp = (struct module_cb*)xmalloc(sizeof(struct module_cb)); without any "check and die" on its own. Note that if this were a new code that adds a call to xmalloc(), competent reviewers would say it should be spelled more like so: temp = xmalloc(sizeof(*temp)); to lose unnecessary cast and to prepare for future evolution of the code (e.g. the type of 'temp' may change from 'struct module_cb' to somethng else). But for this "malloc is wrong, use xmalloc instead" fix, we do not mix such a code improvement in the same patch. Thanks. ```