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Ticket UUID: e4a18565a36884b00edf66541f38c693827968ab
Title: Stale KeyInfo object used in shared-cache mode
Status: Fixed Type: Code_Defect
Severity: Critical Priority: Immediate
Subsystem: Unknown Resolution: Fixed
Last Modified: 2014-12-05 14:44:58
Version Found In: 3.8.5
User Comments:
drh added on 2014-12-05 04:45:14:

The sqlite3KeyInfoOfIndex() routine (here) can return a stale KeyInfo object in shared cache mode.

Scenario:

  • Two open database connections (A and B) on the same cache
  • The shared pIdx object is holding a KeyInfo object for A
  • Connection A closes.
  • Connection C opens, and by (bad) luck is allocated the same database connection pointer as A had.
  • Connection C now tries to get a KeyInfo object for index pIdx but is handed the stale one from A. The KeyInfo object itself is ref-counted and so it is still live. But the KeyInfo points to CollSeq objects within the old A connection that are now dead and have been freed.

This problem appears to have been introduced by check-in [c80e229dd9c1230ab] on 2013-11-07, which first appeared in SQLite version 3.8.2.