[PATCH v3 0/1] binder: fix freeze race

[Li Li]

From: Li Li <dualli at google.com>

As there isn't an atomic operation to freeze the main thread and binder
interface together, it's possible the main thread initiates a new binder
transaction while the binder interfaces are already frozen. This race issue
will result in failed binder transaction and unexpectedly crash the app.

This patch allows a post-froze rollback mechanism by checking if there's
any new pending binder transaction waiting for response. At the same time,
it treats the response transaction like an oneway transaction so that the
response can successfully reach the frozen process.

Changes in v2:
1. Improve commit msg, adding "Fixes";
2. Adding missing "_ilocked" suffix to binder_txns_pending();
3. Document bit assignment of struct binder_frozen_status_info in binder.h.

Changes in v3:
1. Make function binder_txns_pending() bool;
2. Remove redundant outstanding_txns check in binder_ioctl_freeze;
3. Change local variable txns_pending from int to __u32 for alignment;
4. Clarify uapi backward compatibility in commit msg.

Li Li (1):
  binder: fix freeze race

 drivers/android/binder.c            | 35 ++++++++++++++++++++++++-----
 drivers/android/binder_internal.h   |  2 ++
 include/uapi/linux/android/binder.h |  7 ++++++
 3 files changed, 38 insertions(+), 6 deletions(-)

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2.33.0.309.g3052b89438-goog