From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4A7542C027B; Thu, 15 Jan 2026 17:17:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768497467; cv=none; b=k9wcp/RNJUthbXx2GVC65dXl16T9nZKR98IJ47lN2mRH+zkm82j6FF1y5boqCgDXRYiYZYGU02J4RfiyGUdnryB4+a5cAcDF8Vwmk0qupMWKHgQYFO+ckxfdgtsFhOuZfa0MVYR6+ic0sihwBCAenzvRNyyK3GdS7OGJS4ZGdLI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768497467; c=relaxed/simple; bh=LKap9feVQU1Y5inFDr4Je8bEaukejtJre1UlfLtljRU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=JZIuVQVPFkhcahVKVsSSFg/IPikqGec88wxraZFxe/XvXdwurqXBFzydTB0bUP0d9+5XgX/S4mZFqgkQR02LmjN7p3GIfrhIIhl/ypColgo2lPyHGuR4Hq9k5mDikrLSNK8yBA6O8PDQOTCWqkPuEAJHB9xBUC3PGqhDemESPOI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=lUxxcnqu; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="lUxxcnqu" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CA091C16AAE; Thu, 15 Jan 2026 17:17:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1768497467; bh=LKap9feVQU1Y5inFDr4Je8bEaukejtJre1UlfLtljRU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=lUxxcnquo6GG1viakTKcsRi9Ls4veWVery2Ul47kKKjymgSS/oNd0N6hrMj7WHi86 DfcFwLpNp+n6aM6ktSqDjpt9vyZhARuwHkDFcx5JgtkYIIw46aqAvS51SmHT+82N1g jPzxVAGeCR4wEvnZsKNYtCLw+gn6OjnGtmhJA7Jw= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Long Li , Madhavan Srinivasan , Sasha Levin Subject: [PATCH 5.15 090/554] macintosh/mac_hid: fix race condition in mac_hid_toggle_emumouse Date: Thu, 15 Jan 2026 17:42:36 +0100 Message-ID: <20260115164249.504360590@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260115164246.225995385@linuxfoundation.org> References: <20260115164246.225995385@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Long Li [ Upstream commit 1e4b207ffe54cf33a4b7a2912c4110f89c73bf3f ] The following warning appears when running syzkaller, and this issue also exists in the mainline code. ------------[ cut here ]------------ list_add double add: new=ffffffffa57eee28, prev=ffffffffa57eee28, next=ffffffffa5e63100. WARNING: CPU: 0 PID: 1491 at lib/list_debug.c:35 __list_add_valid_or_report+0xf7/0x130 Modules linked in: CPU: 0 PID: 1491 Comm: syz.1.28 Not tainted 6.6.0+ #3 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014 RIP: 0010:__list_add_valid_or_report+0xf7/0x130 RSP: 0018:ff1100010dfb7b78 EFLAGS: 00010282 RAX: 0000000000000000 RBX: ffffffffa57eee18 RCX: ffffffff97fc9817 RDX: 0000000000040000 RSI: ffa0000002383000 RDI: 0000000000000001 RBP: ffffffffa57eee28 R08: 0000000000000001 R09: ffe21c0021bf6f2c R10: 0000000000000001 R11: 6464615f7473696c R12: ffffffffa5e63100 R13: ffffffffa57eee28 R14: ffffffffa57eee28 R15: ff1100010dfb7d48 FS: 00007fb14398b640(0000) GS:ff11000119600000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 000000010d096005 CR4: 0000000000773ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 80000000 Call Trace: input_register_handler+0xb3/0x210 mac_hid_start_emulation+0x1c5/0x290 mac_hid_toggle_emumouse+0x20a/0x240 proc_sys_call_handler+0x4c2/0x6e0 new_sync_write+0x1b1/0x2d0 vfs_write+0x709/0x950 ksys_write+0x12a/0x250 do_syscall_64+0x5a/0x110 entry_SYSCALL_64_after_hwframe+0x78/0xe2 The WARNING occurs when two processes concurrently write to the mac-hid emulation sysctl, causing a race condition in mac_hid_toggle_emumouse(). Both processes read old_val=0, then both try to register the input handler, leading to a double list_add of the same handler. CPU0 CPU1 ------------------------- ------------------------- vfs_write() //write 1 vfs_write() //write 1 proc_sys_write() proc_sys_write() mac_hid_toggle_emumouse() mac_hid_toggle_emumouse() old_val = *valp // old_val=0 old_val = *valp // old_val=0 mutex_lock_killable() proc_dointvec() // *valp=1 mac_hid_start_emulation() input_register_handler() mutex_unlock() mutex_lock_killable() proc_dointvec() mac_hid_start_emulation() input_register_handler() //Trigger Warning mutex_unlock() Fix this by moving the old_val read inside the mutex lock region. Fixes: 99b089c3c38a ("Input: Mac button emulation - implement as an input filter") Signed-off-by: Long Li Signed-off-by: Madhavan Srinivasan Link: https://patch.msgid.link/20250819091035.2263329-1-leo.lilong@huaweicloud.com Signed-off-by: Sasha Levin --- drivers/macintosh/mac_hid.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/macintosh/mac_hid.c b/drivers/macintosh/mac_hid.c index 28b8581b44dda..b622df9f4b231 100644 --- a/drivers/macintosh/mac_hid.c +++ b/drivers/macintosh/mac_hid.c @@ -186,13 +186,14 @@ static int mac_hid_toggle_emumouse(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos) { int *valp = table->data; - int old_val = *valp; + int old_val; int rc; rc = mutex_lock_killable(&mac_hid_emumouse_mutex); if (rc) return rc; + old_val = *valp; rc = proc_dointvec(table, write, buffer, lenp, ppos); if (rc == 0 && write && *valp != old_val) { -- 2.51.0