linux-kernel - [PATCH v2] mm/slub: clean up create_unique

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Date:   Sun, 25 Sep 2022 15:12:07 +0800
From:   Chao Yu <chao@...nel.org>
To:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hugh Dickins <hugh@...itas.com>
Cc:     chao@...nel.org, Chao Yu <chao.yu@...o.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] mm/slub: clean up create_unique_id()

From: Chao Yu <chao.yu@...o.com>

As Christophe JAILLET suggested:

In create_unique_id(),

"looks that ID_STR_LENGTH could even be reduced to 32 or 16.

The 2nd BUG_ON at the end of the function could certainly be just
removed as well or remplaced by a:
        if (p > name + ID_STR_LENGTH - 1) {
                kfree(name);
                return -E<something>;
        }
"

According to above suggestion, let's do below cleanups:
1. reduce ID_STR_LENGTH to 32, as the buffer size should be enough;
2. use WARN_ON instead of BUG_ON() and return error if check condition
is true;
3. use snprintf instead of sprintf to avoid overflow.

Link: https://lore.kernel.org/linux-mm/2025305d-16db-abdf-6cd3-1fb93371c2b4@wanadoo.fr/
Fixes: 81819f0fc828 ("SLUB core")
Suggested-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@...il.com>
Signed-off-by: Chao Yu <chao.yu@...o.com>
---
v2:
- add WARN_ON() instead of return error silently;
- use snprintf instead of sprintf to avoid overflow.
 mm/slub.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 4b98dff9be8e..3d37a8a7b965 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5890,7 +5890,7 @@ static inline struct kset *cache_kset(struct kmem_cache *s)
 	return slab_kset;
 }
 
-#define ID_STR_LENGTH 64
+#define ID_STR_LENGTH 32
 
 /* Create a unique string id for a slab cache:
  *
@@ -5924,9 +5924,13 @@ static char *create_unique_id(struct kmem_cache *s)
 		*p++ = 'A';
 	if (p != name + 1)
 		*p++ = '-';
-	p += sprintf(p, "%07u", s->size);
+	p += snprintf(p, ID_STR_LENGTH - 1 - (p - name), "%07u", s->size);
 
-	BUG_ON(p > name + ID_STR_LENGTH - 1);
+	if (p > name + ID_STR_LENGTH - 1) {
+		WARN_ON(1);
+		kfree(name);
+		return ERR_PTR(-EINVAL);
+	}
 	return name;
 }
 
-- 
2.36.1