don't allow enabling a write back cache on devices that don't support it

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* don't allow enabling a write back cache on devices that don't support it
@ 2023-07-07  9:42 Christoph Hellwig
  2023-07-07  9:42 ` [PATCH 1/2] block: cleanup queue_wc_store Christoph Hellwig
                   ` (3 more replies)
  0 siblings, 4 replies; 6+ messages in thread
From: Christoph Hellwig @ 2023-07-07  9:42 UTC (permalink / raw)
  To: Jens Axboe; +Cc: linux-block

Hi Jens,

this series fixes a case where a user could enable a write back cache
on a device (driver) that doesn't support it all, potentially leading
to flush requests being sent to a driver that doesn't know whast to
do with them.

diffstat:
 block/blk-settings.c   |    7 +++++--
 block/blk-sysfs.c      |   21 ++++++++-------------
 include/linux/blkdev.h |    1 +
 3 files changed, 14 insertions(+), 15 deletions(-)

^ permalink raw reply	[flat|nested] 6+ messages in thread

* [PATCH 1/2] block: cleanup queue_wc_store
  2023-07-07  9:42 don't allow enabling a write back cache on devices that don't support it Christoph Hellwig
@ 2023-07-07  9:42 ` Christoph Hellwig
  2023-07-07  9:42 ` [PATCH 2/2] block: don't allow enabling a cache on devices that don't support it Christoph Hellwig
                   ` (2 subsequent siblings)
  3 siblings, 0 replies; 6+ messages in thread
From: Christoph Hellwig @ 2023-07-07  9:42 UTC (permalink / raw)
  To: Jens Axboe; +Cc: linux-block

Get rid of the local queue_wc_store variable and handling setting and
clearing the QUEUE_FLAG_WC flag diretly instead the if / else if.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-sysfs.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index afc797fb0dfc48..0cde6598fb2f4d 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -449,21 +449,13 @@ static ssize_t queue_wc_show(struct request_queue *q, char *page)
 static ssize_t queue_wc_store(struct request_queue *q, const char *page,
 			      size_t count)
 {
-	int set = -1;
-
 	if (!strncmp(page, "write back", 10))
-		set = 1;
+		blk_queue_flag_set(QUEUE_FLAG_WC, q);
 	else if (!strncmp(page, "write through", 13) ||
 		 !strncmp(page, "none", 4))
-		set = 0;
-
-	if (set == -1)
-		return -EINVAL;
-
-	if (set)
-		blk_queue_flag_set(QUEUE_FLAG_WC, q);
-	else
 		blk_queue_flag_clear(QUEUE_FLAG_WC, q);
+	else
+		return -EINVAL;
 
 	return count;
 }
-- 
2.39.2


^ permalink raw reply related	[flat|nested] 6+ messages in thread

* [PATCH 2/2] block: don't allow enabling a cache on devices that don't support it
  2023-07-07  9:42 don't allow enabling a write back cache on devices that don't support it Christoph Hellwig
  2023-07-07  9:42 ` [PATCH 1/2] block: cleanup queue_wc_store Christoph Hellwig
@ 2023-07-07  9:42 ` Christoph Hellwig
  2023-07-13 13:43 ` don't allow enabling a write back " Christoph Hellwig
  2023-07-15 15:52 ` Jens Axboe
  3 siblings, 0 replies; 6+ messages in thread
From: Christoph Hellwig @ 2023-07-07  9:42 UTC (permalink / raw)
  To: Jens Axboe; +Cc: linux-block

Currently the write_cache attribute allows enabling the QUEUE_FLAG_WC
flag on devices that never claimed the capability.

Fix that by adding a QUEUE_FLAG_HW_WC flag that is set by
blk_queue_write_cache and guards re-enabling the cache through sysfs.

Note that any rescan that calls blk_queue_write_cache will still
re-enable the write cache as in the current code.

Fixes: 93e9d8e836cb ("block: add ability to flag write back caching on a device")
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-settings.c   |  7 +++++--
 block/blk-sysfs.c      | 11 +++++++----
 include/linux/blkdev.h |  1 +
 3 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 4dd59059b788eb..0046b447268f91 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -830,10 +830,13 @@ EXPORT_SYMBOL(blk_set_queue_depth);
  */
 void blk_queue_write_cache(struct request_queue *q, bool wc, bool fua)
 {
-	if (wc)
+	if (wc) {
+		blk_queue_flag_set(QUEUE_FLAG_HW_WC, q);
 		blk_queue_flag_set(QUEUE_FLAG_WC, q);
-	else
+	} else {
+		blk_queue_flag_clear(QUEUE_FLAG_HW_WC, q);
 		blk_queue_flag_clear(QUEUE_FLAG_WC, q);
+	}
 	if (fua)
 		blk_queue_flag_set(QUEUE_FLAG_FUA, q);
 	else
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 0cde6598fb2f4d..63e4812623361d 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -449,13 +449,16 @@ static ssize_t queue_wc_show(struct request_queue *q, char *page)
 static ssize_t queue_wc_store(struct request_queue *q, const char *page,
 			      size_t count)
 {
-	if (!strncmp(page, "write back", 10))
+	if (!strncmp(page, "write back", 10)) {
+		if (!test_bit(QUEUE_FLAG_HW_WC, &q->queue_flags))
+			return -EINVAL;
 		blk_queue_flag_set(QUEUE_FLAG_WC, q);
-	else if (!strncmp(page, "write through", 13) ||
-		 !strncmp(page, "none", 4))
+	} else if (!strncmp(page, "write through", 13) ||
+		 !strncmp(page, "none", 4)) {
 		blk_queue_flag_clear(QUEUE_FLAG_WC, q);
-	else
+	} else {
 		return -EINVAL;
+	}
 
 	return count;
 }
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ed44a997f629f5..2f5371b8482c00 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -538,6 +538,7 @@ struct request_queue {
 #define QUEUE_FLAG_ADD_RANDOM	10	/* Contributes to random pool */
 #define QUEUE_FLAG_SYNCHRONOUS	11	/* always completes in submit context */
 #define QUEUE_FLAG_SAME_FORCE	12	/* force complete on same CPU */
+#define QUEUE_FLAG_HW_WC	18	/* Write back caching supported */
 #define QUEUE_FLAG_INIT_DONE	14	/* queue is initialized */
 #define QUEUE_FLAG_STABLE_WRITES 15	/* don't modify blks until WB is done */
 #define QUEUE_FLAG_POLL		16	/* IO polling enabled if set */
-- 
2.39.2


^ permalink raw reply related	[flat|nested] 6+ messages in thread

* Re: don't allow enabling a write back cache on devices that don't support it
  2023-07-07  9:42 don't allow enabling a write back cache on devices that don't support it Christoph Hellwig
  2023-07-07  9:42 ` [PATCH 1/2] block: cleanup queue_wc_store Christoph Hellwig
  2023-07-07  9:42 ` [PATCH 2/2] block: don't allow enabling a cache on devices that don't support it Christoph Hellwig
@ 2023-07-13 13:43 ` Christoph Hellwig
  2023-07-15 15:50   ` Jens Axboe
  2023-07-15 15:52 ` Jens Axboe
  3 siblings, 1 reply; 6+ messages in thread
From: Christoph Hellwig @ 2023-07-13 13:43 UTC (permalink / raw)
  To: Jens Axboe; +Cc: linux-block

Jens, does this make sense to you?  Without this we can deliver
flush requests to drivers not supporting them, which is a bit nasty
even if it's not exploitable without root-equivalent access.

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: don't allow enabling a write back cache on devices that don't support it
  2023-07-13 13:43 ` don't allow enabling a write back " Christoph Hellwig
@ 2023-07-15 15:50   ` Jens Axboe
  0 siblings, 0 replies; 6+ messages in thread
From: Jens Axboe @ 2023-07-15 15:50 UTC (permalink / raw)
  To: Christoph Hellwig; +Cc: linux-block

On 7/13/23 7:43?AM, Christoph Hellwig wrote:
> Jens, does this make sense to you?  Without this we can deliver
> flush requests to drivers not supporting them, which is a bit nasty
> even if it's not exploitable without root-equivalent access.

Yeah I think so, I'll queue it up for 6.6.

-- 
Jens Axboe


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: don't allow enabling a write back cache on devices that don't support it
  2023-07-07  9:42 don't allow enabling a write back cache on devices that don't support it Christoph Hellwig
                   ` (2 preceding siblings ...)
  2023-07-13 13:43 ` don't allow enabling a write back " Christoph Hellwig
@ 2023-07-15 15:52 ` Jens Axboe
  3 siblings, 0 replies; 6+ messages in thread
From: Jens Axboe @ 2023-07-15 15:52 UTC (permalink / raw)
  To: Christoph Hellwig; +Cc: linux-block


On Fri, 07 Jul 2023 11:42:37 +0200, Christoph Hellwig wrote:
> this series fixes a case where a user could enable a write back cache
> on a device (driver) that doesn't support it all, potentially leading
> to flush requests being sent to a driver that doesn't know whast to
> do with them.
> 
> diffstat:
>  block/blk-settings.c   |    7 +++++--
>  block/blk-sysfs.c      |   21 ++++++++-------------
>  include/linux/blkdev.h |    1 +
>  3 files changed, 14 insertions(+), 15 deletions(-)
> 
> [...]

Applied, thanks!

[1/2] block: cleanup queue_wc_store
      commit: ba2b2594c0e15a40b7f42dd8aca1867c57c13145
[2/2] block: don't allow enabling a cache on devices that don't support it
      commit: 3e8f23e19c95fb4757f8c77f1473578d2154d7c2

Best regards,
-- 
Jens Axboe




^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2023-07-15 15:52 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2023-07-07  9:42 don't allow enabling a write back cache on devices that don't support it Christoph Hellwig
2023-07-07  9:42 ` [PATCH 1/2] block: cleanup queue_wc_store Christoph Hellwig
2023-07-07  9:42 ` [PATCH 2/2] block: don't allow enabling a cache on devices that don't support it Christoph Hellwig
2023-07-13 13:43 ` don't allow enabling a write back " Christoph Hellwig
2023-07-15 15:50   ` Jens Axboe
2023-07-15 15:52 ` Jens Axboe

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