[PATCH] fix null pointer dereference

[PATCH] fix null pointer dereference

[Kleber Tarcísio via GitGitGadget]

From: =?UTF-8?q?Kleber=20Tarc=C3=ADsio?= <klebertarcisio@yahoo.com.br>

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 <klebertarcisio@yahoo.com.br>
---
    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

Re: [PATCH] fix null pointer dereference

[Ævar Arnfjörð Bjarmason]

On Sun, Mar 21 2021, Kleber Tarcísio via GitGitGadget wrote:

> From: =?UTF-8?q?Kleber=20Tarc=C3=ADsio?= <klebertarcisio@yahoo.com.br>
>
> 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 <klebertarcisio@yahoo.com.br>
> ---
>     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.

Re: [PATCH] fix null pointer dereference

[Matheus Tavares Bernardino]

Hi, Kleber. And welcome to the list!

On Sun, Mar 21, 2021 at 7:53 AM Kleber Tarcísio via GitGitGadget
<gitgitgadget@gmail.com> wrote:
>
> From: =?UTF-8?q?Kleber=20Tarc=C3=ADsio?= <klebertarcisio@yahoo.com.br>
>
> 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

Re: [PATCH] fix null pointer dereference

[Junio C Hamano]

"Kleber Tarcísio via GitGitGadget"  <gitgitgadget@gmail.com> writes:

> From: =?UTF-8?q?Kleber=20Tarc=C3=ADsio?= <klebertarcisio@yahoo.com.br>
> Subject: Re: [PATCH] fix null pointer dereference

Thanks, but see Documentation/SubmittingPatches for general guidelines.
Our commit title begins with "<area>:" 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.