Commit bed4b455 authored by Rob Clark's avatar Rob Clark Committed by Tvrtko Ursulin
Browse files

drm/i915: Fix potential context UAFs 



gem_context_register() makes the context visible to userspace, and which
point a separate thread can trigger the I915_GEM_CONTEXT_DESTROY ioctl.
So we need to ensure that nothing uses the ctx ptr after this.  And we
need to ensure that adding the ctx to the xarray is the *last* thing
that gem_context_register() does with the ctx pointer.

Signed-off-by: default avatarRob Clark <robdclark@chromium.org>
Fixes: eb4dedae ("drm/i915/gem: Delay tracking the GEM context until it is registered")
Fixes: a4c1cdd3 ("drm/i915/gem: Delay context creation (v3)")
Fixes: 49bd54b3 ("drm/i915: Track all user contexts per client")
Cc: <stable@vger.kernel.org> # v5.10+
Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: default avatarAndi Shyti <andi.shyti@linux.intel.com>
[tursulin: Stable and fixes tags add/tidy.]
Signed-off-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230103234948.1218393-1-robdclark@gmail.com
parent 4f0755c2

drivers/gpu/drm/i915/gem/i915_gem_context.c

+18 −6
Original line number Diff line number Diff line
@@ -1688,6 +1688,10 @@ void i915_gem_init__contexts(struct drm_i915_private *i915) 
	init_contexts(&i915->gem.contexts);

}



/*

 * Note that this implicitly consumes the ctx reference, by placing

 * the ctx in the context_xa.

 */

static void gem_context_register(struct i915_gem_context *ctx,

				 struct drm_i915_file_private *fpriv,

				 u32 id)
@@ -1703,10 +1707,6 @@ static void gem_context_register(struct i915_gem_context *ctx, 
	snprintf(ctx->name, sizeof(ctx->name), "%s[%d]",

		 current->comm, pid_nr(ctx->pid));



	/* And finally expose ourselves to userspace via the idr */

	old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL);

	WARN_ON(old);



	spin_lock(&ctx->client->ctx_lock);

	list_add_tail_rcu(&ctx->client_link, &ctx->client->ctx_list);

	spin_unlock(&ctx->client->ctx_lock);
@@ -1714,6 +1714,10 @@ static void gem_context_register(struct i915_gem_context *ctx, 
	spin_lock(&i915->gem.contexts.lock);

	list_add_tail(&ctx->link, &i915->gem.contexts.list);

	spin_unlock(&i915->gem.contexts.lock);



	/* And finally expose ourselves to userspace via the idr */

	old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL);

	WARN_ON(old);

}



int i915_gem_context_open(struct drm_i915_private *i915,
@@ -2199,14 +2203,22 @@ finalize_create_context_locked(struct drm_i915_file_private *file_priv, 
	if (IS_ERR(ctx))

		return ctx;



	/*

	 * One for the xarray and one for the caller.  We need to grab

	 * the reference *prior* to making the ctx visble to userspace

	 * in gem_context_register(), as at any point after that

	 * userspace can try to race us with another thread destroying

	 * the context under our feet.

	 */

	i915_gem_context_get(ctx);



	gem_context_register(ctx, file_priv, id);



	old = xa_erase(&file_priv->proto_context_xa, id);

	GEM_BUG_ON(old != pc);

	proto_context_close(file_priv->dev_priv, pc);



	/* One for the xarray and one for the caller */

	return i915_gem_context_get(ctx);

	return ctx;

}



struct i915_gem_context *