From 99343c46d4e2b34c285d3d5f68ff04274c2f9fb4 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 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 --- 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 42a39e103d7c1..6d639ca24dfbb 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c @@ -1860,11 +1860,19 @@ 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; -- 2.30.2