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([102.42.253.8]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4830ec57bcdsm48704285e9.2.2026.02.04.11.57.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Feb 2026 11:57:56 -0800 (PST) From: Osama Abdelkader To: Vlastimil Babka , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Osama Abdelkader , syzbot+6e04171f00f33c0d62fb@syzkaller.appspotmail.com Subject: [PATCH] mm/slub: zero-initialize slab object extensions to fix KMSAN Date: Wed, 4 Feb 2026 20:57:51 +0100 Message-ID: <20260204195751.188219-1-osama.abdelkader@gmail.com> X-Mailer: git-send-email 2.43.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 89B7480005 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: fzqn8x9fq64f3rmt7cjfswihroskga46 X-HE-Tag: 1770235078-68960 X-HE-Meta: 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 UanluGes deDKiTUOqBiOEazZB8REKZa2vqqVHZUvwg4YKgAY8Xlk10Tq5cwyuw4ky05OKP9gGd6s3UqEjk7juNr2JtLsigsG8C4YE21qhK7rEx7R10Ks6eoZ7f90UZr33xpQ1HYoAfTmcpgeYNEKu2kIHmvt+F04trNxmYap6ZQmXKIvM5sO6qblBUuIinK2GDsMxaLxQkv3m9VLgqocUIHz7TTf/base/oyBM8mZP0lszuwQy3AvjPIIDPO8iQ4z/NMRcR83DclgjTHTH30lCXAVLmu5IfIl+j3Xn4QZhSyeMovfpJa42yuohnQUsfOcJGy/9el/1EacRfIIZ8/JunUtShUMGn3fOKBC2sxIuadFGrhxfLOTBSXi3T6ey69rRpvF1nTfQ9yPbpxqjTWvSZ3x4bZVxSf+iZ8r3yW5fmSLpP95/HgWR6xzYTWtH4j1MXgU6KUyNvuJTcZETbNGVVRFTnYO0uO0zOxeH1Mv4WpYcyaptfNnbUQUMXRFjWYJaoKQEuP9j38bYB1FShi+iNs5fTSEmRqGVBeFkW/+QUhWVs3BVCNYk8mjFlxmKdko2y+khbx/dNCvChx8xRfcQ+5D7w3SKmSrkbTYmWHgDxW2uW2IVrQdLuk+T/QXVJnS/cX8rjqwrqf68VPL9z8O4HOpiekami+M+Fs4CAbLIW8y X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: KMSAN reports uninitialized reads in __memcg_slab_free_hook when freeing sigqueue objects. Although kmalloc_nolock(__GFP_ZERO) and kcalloc_node normally zero memory, some allocation paths (fallbacks, early boot, reused slabs, or races) may leave objcg undefined. Explicitly memset the obj_exts array after allocation to guarantee no uninitialized reads in __memcg_slab_free_hook and preserve correct memcg accounting. Reported-by: syzbot+6e04171f00f33c0d62fb@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=6e04171f00f33c0d62fb Signed-off-by: Osama Abdelkader --- mm/slub.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/mm/slub.c b/mm/slub.c index f77b7407c51b..e66d17ee7fa8 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2123,7 +2123,17 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, vec = kcalloc_node(objects, sizeof(struct slabobj_ext), gfp, slab_nid(slab)); } - if (!vec) { + /* + * Explicitly zero the obj_exts array to ensure KMSAN recognizes it + * as initialized. Although kmalloc_nolock and kcalloc_node normally + * zero memory, KMSAN may not track this initialization in all cases, + * especially during early boot or with certain allocation paths. + * This explicit memset ensures KMSAN sees the initialization and + * prevents uninitialized value warnings when accessing objcg fields. + */ + if (vec) + memset(vec, 0, objects * sizeof(*vec)); + else { /* * Try to mark vectors which failed to allocate. * If this operation fails, there may be a racing process -- 2.43.0