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 159601E0E14 for ; Sat, 23 Aug 2025 01:45:21 +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=1755913522; cv=none; b=UV9mK3kNaZR4ebKFM1nqR6/nVMzuZhOBunr44gorFX7BTle1SIKo3aaEBRJeBRPkm8DXKOrA5s3rtxWAmv4o3/JfEeLCoqY38XntZpQgPC7Ex8aLLfXSMlpgoL2d1t/6CLAAL2pt3NKp2PjJsamWRR3X1Nr+yyvJZI/iSBaV+Rg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755913522; c=relaxed/simple; bh=0zMu4nM/4VvX6uGoWUA7zEEDFO09Zbkb0qQ920m+wtw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=scJaVujVHUcsUFq+8CWnaAwUrB5t4IetPHN0eeWRVX+O/ftZBdTYoNX4yAfU77cR7nyaoxVldU1FHrPeY7+V2MSjAXR8PDRsNPVcv8msljA19HVS3qGkY9tY83nzMoVBpwkXJDRf8nSm5pVxK9cOQO48X11EpUauUdFMUpxukmc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CX64GPWB; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="CX64GPWB" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 20B5BC4CEED; Sat, 23 Aug 2025 01:45:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1755913521; bh=0zMu4nM/4VvX6uGoWUA7zEEDFO09Zbkb0qQ920m+wtw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=CX64GPWBWTHAHgCEqJqUwXm5LIr/rV1AkxvxDBUhXo2xYRBytNdty1Be2Or9NLwV8 uqTcqW2THkHQXGb7TRaemilgmcRoqmWr5yCsQbmr84r4XFk3C+zDPvJ9+TB9iBAz+y skyUqVRT/Xt6ZepjyGD57tzqZZ2nw0wcU8GFA1b+kzQrLzE+77iNItEVfdb0k9rlrT h0j3i/u6ogcxZc1carRGwFzpzeoyxVf3WgYACYOpqeNK8KF3lfvcMnLHYn+1XIgtvx Ij0lhZmquCTcOdRPs3jonHiaVGwnfWE/8ldqkAbEX0v1no8auNENjEBhLxgkUKpILB /zzUXkQ55yk5A== From: Sasha Levin To: stable@vger.kernel.org Cc: Gui-Dong Han , Hans Verkuil , Sasha Levin Subject: [PATCH 5.4.y] media: rainshadow-cec: fix TOCTOU race condition in rain_interrupt() Date: Fri, 22 Aug 2025 21:45:18 -0400 Message-ID: <20250823014519.1670171-1-sashal@kernel.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <2025082119-december-ranking-b3a3@gregkh> References: <2025082119-december-ranking-b3a3@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Gui-Dong Han [ Upstream commit 7af160aea26c7dc9e6734d19306128cce156ec40 ] In the interrupt handler rain_interrupt(), the buffer full check on rain->buf_len is performed before acquiring rain->buf_lock. This creates a Time-of-Check to Time-of-Use (TOCTOU) race condition, as rain->buf_len is concurrently accessed and modified in the work handler rain_irq_work_handler() under the same lock. Multiple interrupt invocations can race, with each reading buf_len before it becomes full and then proceeding. This can lead to both interrupts attempting to write to the buffer, incrementing buf_len beyond its capacity (DATA_SIZE) and causing a buffer overflow. Fix this bug by moving the spin_lock() to before the buffer full check. This ensures that the check and the subsequent buffer modification are performed atomically, preventing the race condition. An corresponding spin_unlock() is added to the overflow path to correctly release the lock. This possible bug was found by an experimental static analysis tool developed by our team. Fixes: 0f314f6c2e77 ("[media] rainshadow-cec: new RainShadow Tech HDMI CEC driver") Cc: stable@vger.kernel.org Signed-off-by: Gui-Dong Han Signed-off-by: Hans Verkuil [ drivers/media/cec/usb/rainshadow/ => drivers/media/usb/rainshadow-cec/ ] Signed-off-by: Sasha Levin --- drivers/media/usb/rainshadow-cec/rainshadow-cec.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/media/usb/rainshadow-cec/rainshadow-cec.c b/drivers/media/usb/rainshadow-cec/rainshadow-cec.c index ee870ea1a886..6f8d6797c614 100644 --- a/drivers/media/usb/rainshadow-cec/rainshadow-cec.c +++ b/drivers/media/usb/rainshadow-cec/rainshadow-cec.c @@ -171,11 +171,12 @@ static irqreturn_t rain_interrupt(struct serio *serio, unsigned char data, { struct rain *rain = serio_get_drvdata(serio); + spin_lock(&rain->buf_lock); if (rain->buf_len == DATA_SIZE) { + spin_unlock(&rain->buf_lock); dev_warn_once(rain->dev, "buffer overflow\n"); return IRQ_HANDLED; } - spin_lock(&rain->buf_lock); rain->buf_len++; rain->buf[rain->buf_wr_idx] = data; rain->buf_wr_idx = (rain->buf_wr_idx + 1) & 0xff; -- 2.50.1