Re: [PATCH] dm crypt: fix use of uninitialized percpu_counter in ctr error path

[Mikulas Patocka <mpatocka@redhat.com>]

Accepted, thanks.

Mikulas



On Mon, 9 Nov 2026, Zhao Feng wrote:

> If percpu_counter_init() fails in crypt_ctr() (e.g. when the
> underlying percpu allocation fails under memory pressure or fault
> injection), the error path jumps to "bad", which calls
> crypt_dtr().  crypt_dtr() then evaluates
> WARN_ON(percpu_counter_sum(&cc->n_allocated_pages) != 0) and calls
> percpu_counter_destroy() on a counter that was never initialized,
> because __percpu_counter_init_many() returns -ENOMEM before
> calling raw_spin_lock_init() on fbc->lock.
> 
> With lockdep enabled this triggers "INFO: trying to register
> non-static key" in __percpu_counter_sum(), as reported by syzbot.
> The console additionally shows "crypt: Unknown error (-ENOMEM)"
> because this failure path sets no ti->error.
> 
> Move percpu_counter_init() to right after the allocation of cc,
> before ti->private is set and before any "goto bad" can happen.
> On failure, set ti->error and free cc directly, so that
> crypt_dtr() is only ever called with an initialized counter.
> 
> Reported-by: syzbot+4b232570d625662eaab4@syzkaller.appspotmail.com
> Closes: https://syzbot.org/bug?extid=4b232570d625662eaab4
> Fixes: 5059353df86e ("dm crypt: limit the number of allocated pages")
> Cc: stable@vger.kernel.org
> Signed-off-by: Zhao Feng <zhaofeng2@cmss.chinamobile.com>
> ---
> Not runtime-tested (the syzbot report has no reproducer; the
> failure requires percpu_counter_init() to fail).  The affected
> crypt_ctr() code is identical in current upstream master, so the
> patch applies there as-is.  The Fixes hash was verified against
> the upstream commit that introduced both the init call in
> crypt_ctr() and the teardown in crypt_dtr().
> 
>  drivers/md/dm-crypt.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
> index 1ff16b8264..3e69dcc366 100644
> --- a/drivers/md/dm-crypt.c
> +++ b/drivers/md/dm-crypt.c
> @@ -3249,6 +3249,14 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
>  		ti->error = "Cannot allocate encryption context";
>  		return -ENOMEM;
>  	}
> +
> +	ret = percpu_counter_init(&cc->n_allocated_pages, 0, GFP_KERNEL);
> +	if (ret < 0) {
> +		ti->error = "Cannot initialize page counter";
> +		kfree_sensitive(cc);
> +		return ret;
> +	}
> +
>  	cc->key_size = key_size;
>  	cc->sector_size = (1 << SECTOR_SHIFT);
>  	cc->sector_shift = 0;
> @@ -3260,10 +3268,6 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
>  	crypt_calculate_pages_per_client();
>  	spin_unlock(&dm_crypt_clients_lock);
>  
> -	ret = percpu_counter_init(&cc->n_allocated_pages, 0, GFP_KERNEL);
> -	if (ret < 0)
> -		goto bad;
> -
>  	/* Optional parameters need to be read before cipher constructor */
>  	if (argc > 5) {
>  		ret = crypt_ctr_optional(ti, argc - 5, &argv[5]);
> -- 
> 2.39.2
> 
> 
>