linux-kernel - Re: [PATCH 1/1] drm/i915: fix race condition UAF in i915_perf_add_config

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Date:   Tue, 28 Mar 2023 17:48:15 -0700
From:   Umesh Nerlige Ramappa <umesh.nerlige.ramappa@...el.com>
To:     Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
CC:     Min Li <lm0963hack@...il.com>, <jani.nikula@...ux.intel.com>,
        "Lionel Landwerlin" <lionel.g.landwerlin@...el.com>,
        <joonas.lahtinen@...ux.intel.com>, <rodrigo.vivi@...el.com>,
        <airlied@...il.com>, <daniel@...ll.ch>,
        <intel-gfx@...ts.freedesktop.org>,
        <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] drm/i915: fix race condition UAF in
 i915_perf_add_config_ioctl

On Tue, Mar 28, 2023 at 02:08:47PM +0100, Tvrtko Ursulin wrote:
>
>On 28/03/2023 10:36, Min Li wrote:
>>Userspace can guess the id value and try to race oa_config object creation
>>with config remove, resulting in a use-after-free if we dereference the
>>object after unlocking the metrics_lock.  For that reason, unlocking the
>>metrics_lock must be done after we are done dereferencing the object.
>>
>>Signed-off-by: Min Li <lm0963hack@...il.com>
>
>Fixes: f89823c21224 ("drm/i915/perf: Implement I915_PERF_ADD/REMOVE_CONFIG interface")
>Cc: Lionel Landwerlin <lionel.g.landwerlin@...el.com>
>Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@...el.com>
>Cc: <stable@...r.kernel.org> # v4.14+
>
>>---
>>  drivers/gpu/drm/i915/i915_perf.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>>diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
>>index 824a34ec0b83..93748ca2c5da 100644
>>--- a/drivers/gpu/drm/i915/i915_perf.c
>>+++ b/drivers/gpu/drm/i915/i915_perf.c
>>@@ -4634,13 +4634,13 @@ int i915_perf_add_config_ioctl(struct drm_device *dev, void *data,
>>  		err = oa_config->id;
>>  		goto sysfs_err;
>>  	}
>>-
>>-	mutex_unlock(&perf->metrics_lock);
>>+	id = oa_config->id;
>>  	drm_dbg(&perf->i915->drm,
>>  		"Added config %s id=%i\n", oa_config->uuid, oa_config->id);
>>+	mutex_unlock(&perf->metrics_lock);
>>-	return oa_config->id;
>>+	return id;
>>  sysfs_err:
>>  	mutex_unlock(&perf->metrics_lock);
>
>LGTM.
>
>Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@...el.com>
>
>Umesh or Lionel could you please double check? I can merge if confirmed okay.

LGTM,

Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@...el.com>

Thanks,
Umesh

>
>Regards,
>
>Tvrtko