[PATCH v3 0/3] KEYS: Read keys to internal buffer & then copy to userspace

Waiman Long longman at redhat.com
Fri Mar 13 15:20:59 UTC 2020

 - Reorganize the keyctl_read_key() code to make it more readable as
   suggested by Jarkko Sakkinen.
 - Add patch 3 to use kvmalloc() for safer large buffer allocation as
   suggested by David Howells.

 - Handle NULL buffer and buflen properly in patch 1.
 - Fix a bug in big_key.c.
 - Add patch 2 to handle arbitrary large user-supplied buflen.

The current security key read methods are called with the key semaphore
held.  The methods then copy out the key data to userspace which is
subjected to page fault and may acquire the mmap semaphore. That can
result in circular lock dependency and hence a chance to get into

To avoid such a deadlock, an internal buffer is now allocated for getting
out the necessary data first. After releasing the key semaphore, the
key data are then copied out to userspace sidestepping the circular
lock dependency.

The keyutils test suite was run and the test passed with these patchset
applied without any falure.

Waiman Long (3):
  KEYS: Don't write out to userspace while holding key semaphore
  KEYS: Avoid false positive ENOMEM error on key read
  KEYS: Use kvmalloc() to better handle large buffer allocation

 include/linux/key-type.h                  |  2 +-
 security/keys/big_key.c                   | 11 ++-
 security/keys/encrypted-keys/encrypted.c  |  7 +-
 security/keys/internal.h                  | 14 ++++
 security/keys/keyctl.c                    | 87 ++++++++++++++++++++---
 security/keys/keyring.c                   |  6 +-
 security/keys/request_key_auth.c          |  7 +-
 security/keys/trusted-keys/trusted_tpm1.c | 14 +---
 security/keys/user_defined.c              |  5 +-
 9 files changed, 107 insertions(+), 46 deletions(-)


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