* [PATCH] block: Fix the maximum minor value is blk_alloc_ext_minor()
@ 2022-03-26 14:50 Christophe JAILLET
2022-03-28 8:20 ` Jan Kara
2022-03-28 12:36 ` Jens Axboe
0 siblings, 2 replies; 3+ messages in thread
From: Christophe JAILLET @ 2022-03-26 14:50 UTC (permalink / raw)
To: Jens Axboe, Hannes Reinecke, Jan Kara
Cc: linux-kernel, kernel-janitors, Christophe JAILLET, linux-block
ida_alloc_range(..., min, max, ...) returns values from min to max,
inclusive.
So, NR_EXT_DEVT is a valid idx returned by blk_alloc_ext_minor().
This is an issue because in device_add_disk(), this value is used in:
ddev->devt = MKDEV(disk->major, disk->first_minor);
and NR_EXT_DEVT is '(1 << MINORBITS)'.
So, should 'disk->first_minor' be NR_EXT_DEVT, it would overflow.
Fixes: 22ae8ce8b892 ("block: simplify bdev/disk lookup in blkdev_get")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
#define MKDEV(ma,mi) (((ma) << MINORBITS) | (mi))
This patch is completely speculative, but it seems that idr_alloc() and
ida_alloc_range() don't have the same semantic regarding the upper bound.
idr_alloc() looks exclusive, while ida_alloc_range() is inclusive.
We changed from the first one to the other one in the commit in Fixes:.
---
block/genhd.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/block/genhd.c b/block/genhd.c
index c9a4fc90d3e9..b8b6759d670f 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -335,7 +335,7 @@ int blk_alloc_ext_minor(void)
{
int idx;
- idx = ida_alloc_range(&ext_devt_ida, 0, NR_EXT_DEVT, GFP_KERNEL);
+ idx = ida_alloc_range(&ext_devt_ida, 0, NR_EXT_DEVT - 1, GFP_KERNEL);
if (idx == -ENOSPC)
return -EBUSY;
return idx;
--
2.32.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] block: Fix the maximum minor value is blk_alloc_ext_minor()
2022-03-26 14:50 [PATCH] block: Fix the maximum minor value is blk_alloc_ext_minor() Christophe JAILLET
@ 2022-03-28 8:20 ` Jan Kara
2022-03-28 12:36 ` Jens Axboe
1 sibling, 0 replies; 3+ messages in thread
From: Jan Kara @ 2022-03-28 8:20 UTC (permalink / raw)
To: Christophe JAILLET
Cc: Jens Axboe, Hannes Reinecke, Jan Kara, linux-kernel,
kernel-janitors, linux-block, Matthew Wilcox
On Sat 26-03-22 15:50:46, Christophe JAILLET wrote:
> ida_alloc_range(..., min, max, ...) returns values from min to max,
> inclusive.
>
> So, NR_EXT_DEVT is a valid idx returned by blk_alloc_ext_minor().
>
> This is an issue because in device_add_disk(), this value is used in:
> ddev->devt = MKDEV(disk->major, disk->first_minor);
> and NR_EXT_DEVT is '(1 << MINORBITS)'.
>
> So, should 'disk->first_minor' be NR_EXT_DEVT, it would overflow.
>
> Fixes: 22ae8ce8b892 ("block: simplify bdev/disk lookup in blkdev_get")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Indeed. The patch looks good to me so feel free to add:
Reviewed-by: Jan Kara <jack@suse.cz>
> ---
> #define MKDEV(ma,mi) (((ma) << MINORBITS) | (mi))
>
> This patch is completely speculative, but it seems that idr_alloc() and
> ida_alloc_range() don't have the same semantic regarding the upper bound.
> idr_alloc() looks exclusive, while ida_alloc_range() is inclusive.
>
> We changed from the first one to the other one in the commit in Fixes:.
Yes, this difference is really a landmine. Matthew, why is the semantics of
max parameter for idr_alloc() different from ida_alloc_range() or say
idr_alloc_u32()? It is really easy to introduce subtle bugs with this...
Honza
> ---
> block/genhd.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/block/genhd.c b/block/genhd.c
> index c9a4fc90d3e9..b8b6759d670f 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -335,7 +335,7 @@ int blk_alloc_ext_minor(void)
> {
> int idx;
>
> - idx = ida_alloc_range(&ext_devt_ida, 0, NR_EXT_DEVT, GFP_KERNEL);
> + idx = ida_alloc_range(&ext_devt_ida, 0, NR_EXT_DEVT - 1, GFP_KERNEL);
> if (idx == -ENOSPC)
> return -EBUSY;
> return idx;
> --
> 2.32.0
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] block: Fix the maximum minor value is blk_alloc_ext_minor()
2022-03-26 14:50 [PATCH] block: Fix the maximum minor value is blk_alloc_ext_minor() Christophe JAILLET
2022-03-28 8:20 ` Jan Kara
@ 2022-03-28 12:36 ` Jens Axboe
1 sibling, 0 replies; 3+ messages in thread
From: Jens Axboe @ 2022-03-28 12:36 UTC (permalink / raw)
To: Christophe JAILLET, Hannes Reinecke, Jan Kara
Cc: linux-block, kernel-janitors, linux-kernel
On Sat, 26 Mar 2022 15:50:46 +0100, Christophe JAILLET wrote:
> ida_alloc_range(..., min, max, ...) returns values from min to max,
> inclusive.
>
> So, NR_EXT_DEVT is a valid idx returned by blk_alloc_ext_minor().
>
> This is an issue because in device_add_disk(), this value is used in:
> ddev->devt = MKDEV(disk->major, disk->first_minor);
> and NR_EXT_DEVT is '(1 << MINORBITS)'.
>
> [...]
Applied, thanks!
[1/1] block: Fix the maximum minor value is blk_alloc_ext_minor()
commit: d1868328dec5ae2cf210111025fcbc71f78dd5ca
Best regards,
--
Jens Axboe
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-03-26 14:50 [PATCH] block: Fix the maximum minor value is blk_alloc_ext_minor() Christophe JAILLET
2022-03-28 8:20 ` Jan Kara
2022-03-28 12:36 ` Jens Axboe
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