[PATCH] hwrng: core - reject unknown RNG names

[PATCH] hwrng: core - reject unknown RNG names

[Thorsten Blum]

In rng_current_store(), err is 0 after successfully locking rng_mutex,
and if the requested RNG name cannot be found, the function reports
success even though the current RNG was not changed.

Set err = -ENODEV before searching the RNG list to reject unknown names.

Fixes: 142a27f0a731 ("hwrng: core - Reset user selected rng by writing "" to rng_current")
Cc: stable@vger.kernel.org
Signed-off-by: Thorsten Blum <blum@kernel.org>
---
 drivers/char/hw_random/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 57eeefe90da9..1f9e31cdc7f0 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -376,6 +376,7 @@ static ssize_t rng_current_store(struct device *dev,
 		cur_rng_set_by_user = 1;
 		drop_current_rng();
 	} else {
+		err = -ENODEV;
 		list_for_each_entry(rng, &rng_list, list) {
 			if (sysfs_streq(rng->name, buf)) {
 				err = set_current_rng(rng);

Re: [PATCH] hwrng: core - reject unknown RNG names

[Andy Shevchenko]

On Thu, Sep 24, 2026 at 11:21:13PM +0200, Thorsten Blum wrote:
> In rng_current_store(), err is 0 after successfully locking rng_mutex,
> and if the requested RNG name cannot be found, the function reports
> success even though the current RNG was not changed.
> 
> Set err = -ENODEV before searching the RNG list to reject unknown names.

Yeah, from the

> Fixes: 142a27f0a731 ("hwrng: core - Reset user selected rng by writing "" to rng_current")

it looks like it was the intention, but the mutex_lock_interruptible() rewrites
an error code. That's a good example on why I often tell people to decouple
assignment from the definition and the very same issue might happen and would be
hard to debug later on. Surprisingly this happened in the same patch...

Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] hwrng: core - reject unknown RNG names

[Andy Shevchenko]

On Fri, Sep 25, 2026 at 01:00:39PM +0300, Andy Shevchenko wrote:
> On Thu, Sep 24, 2026 at 11:21:13PM +0200, Thorsten Blum wrote:
> > In rng_current_store(), err is 0 after successfully locking rng_mutex,
> > and if the requested RNG name cannot be found, the function reports
> > success even though the current RNG was not changed.
> > 
> > Set err = -ENODEV before searching the RNG list to reject unknown names.
> 
> Yeah, from the
> 
> > Fixes: 142a27f0a731 ("hwrng: core - Reset user selected rng by writing "" to rng_current")
> 
> it looks like it was the intention, but the mutex_lock_interruptible() rewrites
> an error code. That's a good example on why I often tell people to decouple
> assignment from the definition and the very same issue might happen and would be
> hard to debug later on. Surprisingly this happened in the same patch...
> 
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>

Also

Fixes: cb028f1662a9 ("hwrng: core - remove redundant initialization of variable err")

as that one removed the indeed redundant assignment, but forget to fix the issue.

-- 
With Best Regards,
Andy Shevchenko