Messages in this thread | | | Date | Thu, 5 Jan 2023 16:00:11 +0000 | Subject | Re: [PATCH] drm/i915: Fix potential context UAFs | From | Tvrtko Ursulin <> |
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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+
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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