From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f172.google.com (mail-pf1-f172.google.com [209.85.210.172]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 961D3362151 for ; Mon, 30 Mar 2026 04:43:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774845823; cv=none; b=Uuzs5ApHGOq0pSrvnHbwAbgw9kpg87a7T6XlwW08T6Skj7pkFVmPTF2Cv8dvdBU9o0NjpeNc7h8rOIC/W8fFAbH9IzK3s/hURJ22w1qy8uLTdc7tBDL5B3V1R/cW0efinP28/KzbCfZBvGa0ZW8EyX6rBNxrWrKkmaey0r6vZwA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774845823; c=relaxed/simple; bh=I/LoCE7ghR2fhykvvR2K6LR8ap7mzobL/J0+U6S3zt8=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=NgeKzVk5b1Nv+Lp0D2Yj6jLLUYCPt3grjUUOUY+2HnxQSQLj9YtyCR4RhDgBDaarQdYXUQkQv4g08DTVc1bCycvQKlupIvJKU38eNJoSLfwZHyLxDRsz+BkXhQ8JnmtouD/KEn6prMzGWrGTjiTQAVHCK7/VF55ntjCEtt4Ibhc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=pMK0iePC; arc=none smtp.client-ip=209.85.210.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="pMK0iePC" Received: by mail-pf1-f172.google.com with SMTP id d2e1a72fcca58-82a07738118so2226888b3a.0 for ; Sun, 29 Mar 2026 21:43:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1774845822; x=1775450622; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=RVoLlmJXuoZFlO/T8+1qY4HcBw6xf89P3loI3tBHNJg=; b=pMK0iePCS5aflif8zwUM+BeK5h6mjM7yWshMb/Wjo3apEL74HB7aJY4SsW/peIEx1o DgvSW+BiXdCQXjJsJ2a9VjnF7TA8NLj00Z+AKQYeKzU2tNGJCTBHFtbEuD0MSMTfSZn2 gm5Ak9CJ4CEca8pR3Bzt7XX3/Ar106N+0gpDzLaGMexUJWwsLI35mmCCKBkCJFzYtKti 8Hd52F7zKOxql6I/OfRR3ua775/HvJmeQdQDSEQCwtPkHQnPZzXWmDsHr7QwLMxhP/li yIryBxCd+LG7rz/JMGifF13yYzRQYzwdgJrOcRm6waE+kMO8IxwA6bpZ0eudHCbDCU3Z 8xOg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1774845822; x=1775450622; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=RVoLlmJXuoZFlO/T8+1qY4HcBw6xf89P3loI3tBHNJg=; b=QBIY6I89w89tvorpz8EadB083A+HWD/WzWOxhcBUEtLIOg/bunoBzpP/f1GD741MUP EUKLh2ouxlR7KgOF7UyO1LY4WJQyQ1wKiDJW8QgKAYQB9s/Gx/lknoEy4Hefkgnqe86e p+btcUHtA9mJPoRopZ054NKlacJC05dnJspT/v/WgwT5nBgPqNH0+9NqdEjdLmjUWqE9 bn5yQ+akRC54si6XTF/1csN4nUoWqwscWCNkgToe7RaLWtSL58CmjqnU8XmgbHXVgsLc a6dB7pK0fTNpDIlDziyLVwQrZG2FkFBD/xrxoYnYrhGKB6rKkzdE88jjp7ptwrFK8f1C TK0w== X-Forwarded-Encrypted: i=1; AJvYcCVfcLp9xKYnSUFjUzae50AbI0t3VG/3SShFNSK8POB2QagHxlkg153EjAYOfB+yBrenpsWD9afqqh3FEQ==@vger.kernel.org X-Gm-Message-State: AOJu0YyYXQJvkvd0FfPn3+28pioqODz6k2ZX+1db68FDS3DnyxBPvdE1 BgeorPMQZXIpySiyD2tlWLDw7I0QF/gB38+1LL4HOHBrLVJPqU31r973 X-Gm-Gg: ATEYQzw0c50H3iTF+TmsxNMTx2BuM68nrYGn87f2UuNmVHNu7Hf7vUfby+F24dcfhyd MxB1AL3Ewisnt3oK8mw13b5CYSdBYs8AdCOr5VeTzbQD7Cl5xDZWSkxKOcbWEwsgMlYZabafT9+ ADUvKVRwiwqAjwCVMYtiGNzbHeJ8CkF01BDwZHYWQ68mU+Ej+TMlGz+aNpCtevpFWbGK9HoVKOm 8vAHc5FJvWcu5d4yj87YbZT1wV5Yu4/LRNPPtqFiiTglkGeElpE6TjHhJi/HwrwsX1q19RVbnP/ 7Y8CwElf6Ln6edvZ4OuUJhqEr72wdgkj5wLja50ypantFUvxK5n0WevF2Gay1PiSS5nZGn/7FOF XkFKlTKl0m6eIbTgC44ZXQLLYfKA1u9D7qpYYtUuZEExpnEbw7Cs8TMiVO1C6HvDVy5sdeCMCrb YQRnyTfPhLqEhjhEqEISmkgeOqSR3gQh39ZeyNNbP1eCAteLXKTfv4uyVrdmOJkh3zq8zUgGjsO tzaUpw= X-Received: by 2002:a05:6a00:b95:b0:81f:9b4c:81c0 with SMTP id d2e1a72fcca58-82c9608696cmr10223841b3a.41.1774845821829; Sun, 29 Mar 2026 21:43:41 -0700 (PDT) Received: from deepanshu-kernel-hacker.. ([2405:201:682f:389d:d8f3:146b:e2bb:b2f0]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82ca8464576sm6075154b3a.14.2026.03.29.21.43.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 29 Mar 2026 21:43:41 -0700 (PDT) From: Deepanshu Kartikey To: axboe@kernel.dk, tytso@mit.edu, dvyukov@google.com Cc: adilger.kernel@dilger.ca, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org, Deepanshu Kartikey , syzbot+fb32afec111a7d61b939@syzkaller.appspotmail.com Subject: [PATCH] loop: block loop reconfiguration of offset/sizelimit on mounted device Date: Mon, 30 Mar 2026 10:13:34 +0530 Message-ID: <20260330044334.373480-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit LOOP_SET_STATUS{64} allows changing lo_offset and lo_sizelimit while a filesystem is mounted on the loop device. This effectively mutates the data visible to the mounted filesystem, which is equivalent to writing directly to the block device. When bdev_allow_write_mounted is false, direct writes to a mounted block device are blocked via bdev_writes_blocked(). However, LOOP_SET_STATUS{64} bypasses this protection because it modifies the loop configuration through an ioctl rather than opening the block device for writing. Fix this by checking bdev_writes_blocked() before allowing changes to lo_offset or lo_sizelimit. If the loop device has writes blocked (indicating a filesystem is mounted with write protection), return -EBUSY. Other loop status fields that do not affect the visible data can still be changed while mounted. Export bdev_writes_blocked() so it can be used from the loop driver. Suggested-by: Theodore Ts'o Reported-by: syzbot+fb32afec111a7d61b939@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=fb32afec111a7d61b939 Tested-by: syzbot+fb32afec111a7d61b939@syzkaller.appspotmail.com Signed-off-by: Deepanshu Kartikey --- block/bdev.c | 4 +++- drivers/block/loop.c | 12 ++++++++++++ include/linux/blkdev.h | 1 + 3 files changed, 16 insertions(+), 1 deletion(-) diff --git a/block/bdev.c b/block/bdev.c index ed022f8c48c7..96520fac7b2f 100644 --- a/block/bdev.c +++ b/block/bdev.c @@ -860,10 +860,12 @@ void blkdev_put_no_open(struct block_device *bdev) put_device(&bdev->bd_device); } -static bool bdev_writes_blocked(struct block_device *bdev) +bool bdev_writes_blocked(struct block_device *bdev) { return bdev->bd_writers < 0; } +EXPORT_SYMBOL_GPL(bdev_writes_blocked); + static void bdev_block_writes(struct block_device *bdev) { diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 0000913f7efc..3f3a29abad1f 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1239,6 +1239,18 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info) goto out_unlock; } + /* + * Changing lo_offset or lo_sizelimit on a mounted device is + * equivalent to modifying the block device contents, block + * this if writes are blocked on the device. + */ + if ((lo->lo_offset != info->lo_offset || + lo->lo_sizelimit != info->lo_sizelimit) && + bdev_writes_blocked(lo->lo_device)) { + err = -EBUSY; + goto out_unlock; + } + if (lo->lo_offset != info->lo_offset || lo->lo_sizelimit != info->lo_sizelimit) { size_changed = true; diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index d463b9b5a0a5..6b908e9dd035 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -820,6 +820,7 @@ static inline bool bdev_read_only(struct block_device *bdev) return bdev_test_flag(bdev, BD_READ_ONLY) || get_disk_ro(bdev->bd_disk); } +bool bdev_writes_blocked(struct block_device *bdev); bool set_capacity_and_notify(struct gendisk *disk, sector_t size); void disk_force_media_change(struct gendisk *disk); void bdev_mark_dead(struct block_device *bdev, bool surprise); -- 2.43.0