Avoid exposing a partially constructed context by deferring the list_add() from the initial construction to the end of registration. Otherwise, if we peek into the list of contexts from inside debugfs, we may see the partially constructed context and chase down some dangling incomplete pointers.

Reported-by: CQ Tang cq.tang@intel.com Fixes: 3aa9945a528e ("drm/i915: Separate GEM context construction and registration to userspace") References: f6e8aa387171 ("drm/i915: Report the number of closed vma held by each context in debugfs") Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Tvrtko Ursulin tvrtko.ursulin@intel.com Cc: CQ Tang cq.tang@intel.com Cc: stable@vger.kernel.org # v5.2+ Reviewed-by: Mika Kuoppala mika.kuoppala@linux.intel.com --- drivers/gpu/drm/i915/gem/i915_gem_context.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c index f43f0ca4eec9..d308cefb2b34 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c @@ -713,6 +713,7 @@ __create_context(struct drm_i915_private *i915) ctx->i915 = i915; ctx->sched.priority = I915_USER_PRIORITY(I915_PRIORITY_NORMAL); mutex_init(&ctx->mutex); + INIT_LIST_HEAD(&ctx->link);

spin_lock_init(&ctx->stale.lock); INIT_LIST_HEAD(&ctx->stale.engines); @@ -740,10 +741,6 @@ __create_context(struct drm_i915_private *i915) for (i = 0; i < ARRAY_SIZE(ctx->hang_timestamp); i++) ctx->hang_timestamp[i] = jiffies - CONTEXT_FAST_HANG_JIFFIES;

- spin_lock(&i915->gem.contexts.lock); - list_add_tail(&ctx->link, &i915->gem.contexts.list); - spin_unlock(&i915->gem.contexts.lock); - return ctx;

err_free: @@ -936,6 +933,7 @@ static int gem_context_register(struct i915_gem_context *ctx, struct drm_i915_file_private *fpriv, u32 *id) { + struct drm_i915_private *i915 = ctx->i915; struct i915_address_space *vm; int ret;

@@ -954,8 +952,16 @@ static int gem_context_register(struct i915_gem_context *ctx, /* And finally expose ourselves to userspace via the idr */ ret = xa_alloc(&fpriv->context_xa, id, ctx, xa_limit_32b, GFP_KERNEL); if (ret) - put_pid(fetch_and_zero(&ctx->pid)); + goto err_pid; + + spin_lock(&i915->gem.contexts.lock); + list_add_tail(&ctx->link, &i915->gem.contexts.list); + spin_unlock(&i915->gem.contexts.lock); + + return 0;

+err_pid: + put_pid(fetch_and_zero(&ctx->pid)); return ret; }