** Changed in: linux (Ubuntu Bionic)
       Status: In Progress => Fix Committed

** Changed in: linux (Ubuntu Focal)
       Status: In Progress => Fix Committed

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  apparmor reference leak causes refcount_t overflow with

Status in linux package in Ubuntu:
  Fix Committed
Status in linux source package in Bionic:
  Fix Committed
Status in linux source package in Eoan:
  Fix Committed
Status in linux source package in Focal:
  Fix Committed
Status in linux source package in Groovy:

Bug description:

   * Users of the Crypto (user-space) API (i.e., AF_ALG)
     can trigger refcount errors in AppArmor under high
     load (might lead to memory leak or use after free.)

   * There is a reference leak in AppArmor when af_alg_accept()
     calls security_sock_graft() and then security_sk_clone().

   * Both acquire a reference to a label, to assign it to the
     same pointer, but the latter does not release the former's
     acquired reference (before overwriting the pointer value.)

   * This reference leak builds up over time, and under high
     load can eventually overflow/underflow/saturate refcount,
     depending on which value it has when a program hits that.

   * The fix just checks if the pointer has an assigned label,
     then releases its acquired reference.

  [Test Case]

   * See comment #1 for the test-case 'aa-refcnt-af_alg.c'.

   * Exercise that code path indefinitely until it hits
     the refcount_t overflow/underflow/saturate message
     (or not, with the patch.) (see comment #4)

   * It's possible to monitor refcount values with kprobes,
     to confirm whether or not the problem is happening.
     (see comments #2 and #3)

  [Other Info]

   * Patch applied upstream on v5.8-rc1 [1]
   * Applied on Unstable (tag Ubuntu-5.8-5.8.0-0.1)
   * Not required on Groovy (still 5.4; should sync from Unstable)
   * Not required on Eoan (EOL date before SRU cycle release date)
   * Required on Bionic and Focal.


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