linux-kernel - [PATCH linux-next] alloc_tag: Fix boot failure due to NULL pointer dereference

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Message-ID: <20250926080659.741991-1-ranxiaokai627@163.com>
Date: Fri, 26 Sep 2025 08:06:59 +0000
From: ranxiaokai627@....com
To: vbabka@...e.cz,
	akpm@...ux-foundation.org,
	cl@...two.org,
	rientjes@...gle.com,
	roman.gushchin@...ux.dev,
	harry.yoo@...cle.com,
	usamaarif642@...il.com,
	surenb@...gle.com,
	shakeel.butt@...ux.dev,
	hannes@...xchg.org
Cc: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	ran.xiaokai@....com.cn,
	ranxiaokai627@....com
Subject: [PATCH linux-next] alloc_tag: Fix boot failure due to NULL pointer dereference

From: Ran Xiaokai <ran.xiaokai@....com.cn>

There is a boot failure when both CONFIG_DEBUG_KMEMLEAK and
CONFIG_MEM_ALLOC_PROFILING are enabled.

BUG: kernel NULL pointer dereference, address: 0000000000000000
RIP: 0010:__alloc_tagging_slab_alloc_hook+0x181/0x2f0
Call Trace:
 kmem_cache_alloc_noprof+0x1c8/0x5c0
 __alloc_object+0x2f/0x290
 __create_object+0x22/0x80
 kmemleak_init+0x122/0x190
 mm_core_init+0xb6/0x160
 start_kernel+0x39f/0x920
 x86_64_start_reservations+0x18/0x30
 x86_64_start_kernel+0x104/0x120
 common_startup_64+0x12c/0x138

In kmemleak, mem_pool_alloc() directly calls kmem_cache_alloc_noprof(),
as a result, the alloc_tag structure associated with object_cache is not
defined neither initialized. So current->alloc_tag is NULL,
leading to a null pointer dereference.

Move the checks for SLAB_NO_OBJ_EXT, SLAB_NOLEAKTRACE, and
__GFP_NO_OBJ_EXT to the parent function __alloc_tagging_slab_alloc_hook()
to fix this.

Also this distinguishes the SLAB_NOLEAKTRACE case between the actual memory
allocation failures case, make CODETAG_FLAG_INACCURATE more accurate.

Fixes: b9e2f58ffb84 ("alloc_tag: mark inaccurate allocation counters in /proc/allocinfo output")
Signed-off-by: Ran Xiaokai <ran.xiaokai@....com.cn>
---
 mm/slub.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 867a07260acf..09cbe580842c 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2197,15 +2197,6 @@ prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
 {
 	struct slab *slab;
 
-	if (!p)
-		return NULL;
-
-	if (s->flags & (SLAB_NO_OBJ_EXT | SLAB_NOLEAKTRACE))
-		return NULL;
-
-	if (flags & __GFP_NO_OBJ_EXT)
-		return NULL;
-
 	slab = virt_to_slab(p);
 	if (!slab_obj_exts(slab) &&
 	    alloc_slab_obj_exts(slab, s, flags, false)) {
@@ -2223,6 +2214,15 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags)
 {
 	struct slabobj_ext *obj_exts;
 
+	if (!object)
+		return;
+
+	if (s->flags & (SLAB_NO_OBJ_EXT | SLAB_NOLEAKTRACE))
+		return;
+
+	if (flags & __GFP_NO_OBJ_EXT)
+		return;
+
 	obj_exts = prepare_slab_obj_exts_hook(s, flags, object);
 	/*
 	 * Currently obj_exts is used only for allocation profiling.
-- 
2.25.1