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Mon, 02 Nov 2026 04:29:02 -0800 (PST) Received: from fedora ([2409:40d2:102d:42fe:94:1c18:1e05:91ee]) by smtp.gmail.com with ESMTPSA id af79cd13be357-94425852274sm825390585a.19.2026.11.02.04.28.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Nov 2026 04:29:02 -0800 (PST) From: Sajal Gupta To: Song Liu , Yu Kuai Cc: Li Nan , Xiao Ni , linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org, Sajal Gupta , syzbot+dcad997ed2b5bd95cc5e@syzkaller.appspotmail.com Subject: [PATCH] md: fix use-after-free in md_attr_store() Date: Mon, 2 Nov 2026 17:53:04 +0530 Message-ID: <20261102122430.39209-1-sajal2005gupta@gmail.com> X-Mailer: git-send-email 2.56.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit md_attr_store() calls sysfs_break_active_protection() for a "clear" write to array_state before it calls mddev_get(). sysfs_break_active_protection() does kobject_get() on the mddev kobject. If the array is concurrently being deleted, the kobject refcount can already be zero, which triggers "refcount_t: addition on 0; use-after-free". Fix by calling mddev_get() first. If the array is being deleted it fails with -EBUSY before the kobject is touched, and if it succeeds the array cannot be freed until mddev_put(). The -EBUSY path no longer needs to call sysfs_unbreak_active_protection(). Fixes: 9e59d609763f ("md: call del_gendisk in control path") Reported-by: syzbot+dcad997ed2b5bd95cc5e@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=dcad997ed2b5bd95cc5e Tested-by: syzbot+dcad997ed2b5bd95cc5e@syzkaller.appspotmail.com Signed-off-by: Sajal Gupta --- drivers/md/md.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/drivers/md/md.c b/drivers/md/md.c index 03e35386a802..26f17dd24bdf 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -6163,17 +6163,16 @@ md_attr_store(struct kobject *kobj, struct attribute *attr, if (!capable(CAP_SYS_ADMIN)) return -EACCES; - if (entry->store == array_state_store && cmd_match(page, "clear")) - kn = sysfs_break_active_protection(kobj, attr); - spin_lock(&all_mddevs_lock); if (!mddev_get(mddev)) { spin_unlock(&all_mddevs_lock); - if (kn) - sysfs_unbreak_active_protection(kn); return -EBUSY; } spin_unlock(&all_mddevs_lock); + + if (entry->store == array_state_store && cmd_match(page, "clear")) + kn = sysfs_break_active_protection(kobj, attr); + rv = entry->store(mddev, page, length); /* -- 2.56.0