linux-kernel - Re: [PATCH v3] block: add allocation size check in blkdev_pr_read

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Message-ID: <20251217140513.GA43988@fedora>
Date: Wed, 17 Dec 2025 09:05:13 -0500
From: Stefan Hajnoczi <stefanha@...hat.com>
To: Deepanshu Kartikey <kartikey406@...il.com>
Cc: axboe@...nel.dk, martin.petersen@...cle.com, hare@...e.de,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	syzbot+660d079d90f8a1baf54d@...kaller.appspotmail.com
Subject: Re: [PATCH v3] block: add allocation size check in
 blkdev_pr_read_keys()

On Wed, Dec 17, 2025 at 07:17:12AM +0530, Deepanshu Kartikey wrote:
> blkdev_pr_read_keys() takes num_keys from userspace and uses it to
> calculate the allocation size for keys_info via struct_size(). While
> there is a check for SIZE_MAX (integer overflow), there is no upper
> bound validation on the allocation size itself.
> 
> A malicious or buggy userspace can pass a large num_keys value that
> doesn't trigger overflow but still results in an excessive allocation
> attempt, causing a warning in the page allocator when the order exceeds
> MAX_PAGE_ORDER.
> 
> Fix this by introducing PR_KEYS_MAX to limit the number of keys to
> a sane value. This makes the SIZE_MAX check redundant, so remove it.
> Also switch to kvzalloc/kvfree to handle larger allocations gracefully.
> 
> Fixes: 22a1ffea5f80 ("block: add IOC_PR_READ_KEYS ioctl")
> Tested-by: syzbot+660d079d90f8a1baf54d@...kaller.appspotmail.com
> Reported-by: syzbot+660d079d90f8a1baf54d@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=660d079d90f8a1baf54d
> Link: https://lore.kernel.org/all/20251212013510.3576091-1-kartikey406@gmail.com/T/ [v1]
> Signed-off-by: Deepanshu Kartikey <kartikey406@...il.com>
> ---
> v3:
>   - Renamed PR_KEYS_MAX_NUM to PR_KEYS_MAX
>   - Moved define to include/uapi/linux/pr.h
> v2:
>   - Added PR_KEYS_MAX_NUM (64K) limit instead of checking KMALLOC_MAX_SIZE
>   - Removed redundant SIZE_MAX check
>   - Switched to kvzalloc/kvfree
> ---
>  block/ioctl.c           | 9 +++++----
>  include/uapi/linux/pr.h | 2 ++
>  2 files changed, 7 insertions(+), 4 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@...hat.com>

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