linux-kernel - [PATCH v2] nvme: Define compat_ioctl again to unbreak 32-bit userspace.

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Date:   Wed, 20 Jul 2022 23:57:35 -0400
From:   Nick Bowler <nbowler@...conx.ca>
To:     linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Christoph Hellwig <hch@....de>,
        Guixin Liu <kanie@...ux.alibaba.com>
Subject: [PATCH v2] nvme: Define compat_ioctl again to unbreak 32-bit userspace.

Commit 89b3d6e60550 ("nvme: simplify the compat ioctl handling") removed
the initialization of compat_ioctl from the nvme block_device_operations
structures.

Presumably the expectation was that 32-bit ioctls would be directed
through the regular handler but this is not the case: failing to assign
.compat_ioctl actually means that the compat case is disabled entirely,
and any attempt to submit nvme ioctls from 32-bit userspace fails
outright with -ENOTTY.

For example:

  % smartctl -x /dev/nvme0n1
  [...]
  Read NVMe Identify Controller failed: NVME_IOCTL_ADMIN_CMD: Inappropriate ioctl for device

The blkdev_compat_ptr_ioctl helper can be used to direct compat calls
through the main ioctl handler and makes things work again.

Fixes: 89b3d6e60550 ("nvme: simplify the compat ioctl handling")
Signed-off-by: Nick Bowler <nbowler@...conx.ca>
---

v2: use blkdev_compat_ptr_ioctl as suggested by Christoph Hellwig

 drivers/nvme/host/core.c      | 1 +
 drivers/nvme/host/multipath.c | 1 +
 2 files changed, 2 insertions(+)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 6a12a906a11e..9c75d7378d31 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -2123,6 +2123,7 @@ static int nvme_report_zones(struct gendisk *disk, sector_t sector,
 static const struct block_device_operations nvme_bdev_ops = {
 	.owner		= THIS_MODULE,
 	.ioctl		= nvme_ioctl,
+	.compat_ioctl	= blkdev_compat_ptr_ioctl,
 	.open		= nvme_open,
 	.release	= nvme_release,
 	.getgeo		= nvme_getgeo,
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index d3e2440d8abb..432ea9793a84 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -408,6 +408,7 @@ const struct block_device_operations nvme_ns_head_ops = {
 	.open		= nvme_ns_head_open,
 	.release	= nvme_ns_head_release,
 	.ioctl		= nvme_ns_head_ioctl,
+	.compat_ioctl	= blkdev_compat_ptr_ioctl,
 	.getgeo		= nvme_getgeo,
 	.report_zones	= nvme_ns_head_report_zones,
 	.pr_ops		= &nvme_pr_ops,
-- 
2.35.1