linux-kernel - [PATCH] fix: Prevent memory leak by checking for NULL buffer before calling css

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Message-ID: <CAGFP0L+BaNAtCF7c7cJ1bvbjomp03Fy0=6=w6dj29Fnr0ygSCA@mail.gmail.com>
Date: Mon, 3 Jun 2024 21:33:19 +0900
From: Geunsik Lim <geunsik.lim@...il.com>
To: Axel Rasmussen <axelrasmussen@...gle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Ingo Molnar <mingo@...e.hu>, Andrew Morton <akpm@...ux-foundation.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, 
	Hugh Dickins <hughd@...gle.com>
Cc: "H. Peter Anvin" <hpa@...or.com>, Steven Rostedt <rostedt@...dmis.org>, 
	linux-kernel <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>
Subject: [PATCH] fix: Prevent memory leak by checking for NULL buffer before
 calling css_put()

This commit addresses a potential memory leak in the
`get_mm_memcg_path()` function
by explicitly checking if the allocated buffer (`buf`) is NULL before
calling the
`css_put()` function. The prefix 'css' means abbreviation of cgroup_subsys_state

Previously, the code would directly call `css_put()` without checking
the value of
`buf`, which could lead to a memory leak if the buffer allocation failed.
This commit introduces a conditional check to ensure that `css_put()`
is only called
if `buf` is not NULL.

This change enhances the code's robustness and prevents memory leaks, improving
overall system stability.

**Specific Changes:**

* In the `out_put` label, an `if` statement is added to check
  if `buf` is not NULL before calling `css_put()`.

**Benefits:**

* Prevents potential memory leaks
* Enhances code robustness
* Improves system stability

Signed-off-by: Geunsik Lim <leemgs@...il.com>
Signed-off-by: Geunsik Lim <geunsik.lim@...sung.com>
---
 mm/mmap_lock.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c
index 1854850b4b89..7314045b0e3b 100644
--- a/mm/mmap_lock.c
+++ b/mm/mmap_lock.c
@@ -213,7 +213,8 @@ static const char *get_mm_memcg_path(struct mm_struct *mm)
        cgroup_path(memcg->css.cgroup, buf, MEMCG_PATH_BUF_SIZE);

 out_put:
-       css_put(&memcg->css);
+        if (buf != NULL)
+                css_put(&memcg->css);
 out:
        return buf;
 }
--
2.34.1
----
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