Messages in this thread | | | Date | Fri, 6 Jan 2023 10:15:10 +0000 | Subject | Re: [PATCH] drm/i915: Fix potential context UAFs | From | Tvrtko Ursulin <> |
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On 05/01/2023 16:00, Tvrtko Ursulin wrote: > > On 05/01/2023 15:52, Andi Shyti wrote: >> Hi Rob, >> >> On Tue, Jan 03, 2023 at 03:49:46PM -0800, Rob Clark wrote: >>> From: Rob Clark <robdclark@chromium.org> >>> >>> 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: Rob Clark <robdclark@chromium.org> >> >> Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com> >> >> I also agree with Tvrtko that we should add Stable: and Fixes:. > > Yeah I'll add them all when merging. Just waiting for full CI results. > It will be like this: > > Fixes: eb4dedae920a ("drm/i915/gem: Delay tracking the GEM context until > it is registered") > Fixes: a4c1cdd34e2c ("drm/i915/gem: Delay context creation (v3)") > Fixes: 49bd54b390c2 ("drm/i915: Track all user contexts per client") > Cc: <stable@vger.kernel.org> # v5.10+
Pushed to drm-intel-gt-next - thanks for the fix and reviews.
Regards,
Tvrtko
> > Regards, > > Tvrtko > >> One little thing, "user after free" is clearer that UAF :) >> >> Thanks, >> Andi >> >>> --- >>> drivers/gpu/drm/i915/gem/i915_gem_context.c | 24 +++++++++++++++------ >>> 1 file changed, 18 insertions(+), 6 deletions(-) >>> >>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c >>> b/drivers/gpu/drm/i915/gem/i915_gem_context.c >>> index 7f2831efc798..6250de9b9196 100644 >>> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c >>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c >>> @@ -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 * >>> -- >>> 2.38.1
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