[PATCH] fix: Prevent memory leak by checking for NULL buffer before calling css_put()

[Geunsik Lim]

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@xxxxxxxxx>
Signed-off-by: Geunsik Lim <geunsik.lim@xxxxxxxxxxx>
---
 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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