From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794403052; b=ndgdQzL8d10bi6K6ww5szfzv+yJSGAaveJ97ky16T8ZLG6GBmVHh2RmQlCBVvQA5LR/P ximNErCsG1jxvyItH5pSaudwVt/5hBYPkyp4x29xlGGADHsGFTqrt8hwzCs3MBqvL4evl bfhr+El55XUcbgl605lBMYJquJovE6E7H4F0UKbG9og63Wa8JsckhPcZrxZpiB3tQ2XKO sl9T+n4xCU9HEorf0UEFx+SP7FHp9AxCmlzt+T3dKVu9xTY4rJdVNB6ZrKVtx5C9BxDmo 6HZ5qhTKcZZY3qYGZOujnFXrwnPu3OxI63oLbEbg6cR8iY3pF3/v9m4vipCXBC0I+gg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794403052; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=mDIvEFooe/t5rmVBm5jYTkMldCxFAEAacdty0nyZwuk=; b=cqOQ1VAUxZql+9Ihkq0YXFsbb1WVwEWmQI1mfK3vg/HMMao69AMvaqj1qnlgVgDK4gfq QCztPWKbmRksoivVDVEA5PGgx5VAY0sIDZg7AyiLFgBIVUK1rPRrriFCBgNYSSG8V1MuH R+VlA9eI1nD1vBPBml1Yt6+Gjng5c53dDkt9kGIc/KdDSxYg9G5LHsSJJS2hn00dDC0dl FoHMj99ZQxx1YJiwnMAFdERq/djukIA6AMj+GKlGx6Ur72WiHMz76j5HRsmQE3TJPuG3c Wxg/eKOXb6qes1PRlxaVTWa8AerCMZiEKJDXXdhYH/P7/iN22lnkBslP1f4T4KJA2eA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b="Y+h5/TqD"; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A98C9606A31C for ; Wed, 11 Nov 2026 13:17:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Y+h5/TqD Received: by smtp.kernel.org (Postfix) with ESMTPSA id C5A531F00A05; Wed, 11 Nov 2026 13:17:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794403052; bh=mDIvEFooe/t5rmVBm5jYTkMldCxFAEAacdty0nyZwuk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Y+h5/TqDFJsmal7eGLmgUB6ZjwL3qPTq/mU6eqKD89QafIRYPb7jlUu5/2x1Yp67b sP6ZPWU8igITqK/v7LlD05JO6tcPDE0Pef59vTUpYNq6caetRpb025egx3wDP2bZBG 0GuHA5SosfBBf7XO8T5lwh9p7sMAtZlSCVmIbUnwuZeUj1C/TYhr//OY4pAjgXm7qa 5Kxs6yIMyXaAEgwxYK0PZgKr0TJREp/4QYtBr/vlqupIwt+y8pfQSjiIESLPjhqzw6 NaqLKGdWsuKoWvRPimoUwT9rtD/b+wZzu73Tbewyi0RcIwjbEMT1mRXjLY3ZykP8sb QU/MGd93lhloQ== From: Sasha Levin To: stable@vger.kernel.org Cc: Dominik Maier , Jens Axboe , Sasha Levin Subject: [PATCH 5.15.y] loop: check for read-write open mode on LOOP_SET_STATUS in lo_compat_ioctl() Date: Wed, 11 Nov 2026 08:17:30 -0500 Message-ID: <20261111131503.1579531-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261107061226-failed-5.15-87409eedc543@kernel.org> References: <20261107061226-failed-5.15-87409eedc543@kernel.org> X-Mailing-List: stable@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 From: Dominik Maier [ Upstream commit 87409eedc543d288cdd49c2174f7d61eca7b8db5 ] lo_ioctl() checks for (mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN) before allowing LOOP_SET_STATUS or LOOP_SET_STATUS64, but not lo_compat_ioctl(), the handler used by 32-bit user space on 64-bit kernels. As a result, on 64-bit kernels with CONFIG_COMPAT=y, a 32-bit unprivileged user-space process holding a read-only (O_RDONLY) file descriptor to an active /dev/loopN device can issue a compat LOOP_SET_STATUS ioctl to modify lo_offset, clear lo_sizelimit to 0 (exposing backing-file data past the configured limit), or alter lo_flags. Enforce the same (mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN) check on LOOP_SET_STATUS in lo_compat_ioctl(). Cc: stable@vger.kernel.org Assisted-by: ARTIST LLM Signed-off-by: Dominik Maier Reviewed-by: Bart Van Assche bvanassche@acm.org Link: https://patch.msgid.link/20261025200740.2064379-1-dmnk@google.com Signed-off-by: Jens Axboe [ sashal: Replaced BLK_OPEN_WRITE with FMODE_WRITE to match the existing fmode_t API. ] Signed-off-by: Sasha Levin --- drivers/block/loop.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 45684136e8376..f130024ffd5f5 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -2020,8 +2020,10 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode, switch(cmd) { case LOOP_SET_STATUS: - err = loop_set_status_compat(lo, - (const struct compat_loop_info __user *)arg); + err = -EPERM; + if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN)) + err = loop_set_status_compat(lo, + (const struct compat_loop_info __user *)arg); break; case LOOP_GET_STATUS: err = loop_get_status_compat(lo, -- 2.53.0