From 764accc2c1b8fd1507be2e7f436c94cdce887a00 Mon Sep 17 00:00:00 2001 From: Rob Clark Date: Thu, 19 Jan 2023 09:32:58 -0800 Subject: [PATCH] drm/i915: Avoid potential vm use-after-free commit 41d419382ec7e257e54b7b6ff0d3623aafb1316d upstream. Adding the vm to the vm_xa table makes it visible to userspace, which could try to race with us to close the vm. So we need to take our extra reference before putting it in the table. Signed-off-by: Rob Clark Reviewed-by: Matthew Auld Fixes: 9ec8795e7d91 ("drm/i915: Drop __rcu from gem_context->vm") Cc: # v5.16+ Signed-off-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20230119173321.2825472-1-robdclark@gmail.com (cherry picked from commit 99343c46d4e2b34c285d3d5f68ff04274c2f9fb4) Signed-off-by: Rodrigo Vivi Signed-off-by: Greg Kroah-Hartman --- drivers/gpu/drm/i915/gem/i915_gem_context.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c index 2353723c..5980288 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c @@ -1861,11 +1861,19 @@ static int get_ppgtt(struct drm_i915_file_private *file_priv, vm = ctx->vm; GEM_BUG_ON(!vm); + /* + * Get a reference for the allocated handle. Once the handle is + * visible in the vm_xa table, userspace could try to close it + * from under our feet, so we need to hold the extra reference + * first. + */ + i915_vm_get(vm); + err = xa_alloc(&file_priv->vm_xa, &id, vm, xa_limit_32b, GFP_KERNEL); - if (err) + if (err) { + i915_vm_put(vm); return err; - - i915_vm_get(vm); + } GEM_BUG_ON(id == 0); /* reserved for invalid/unassigned ppgtt */ args->value = id; -- 2.7.4