OpenAFS Master Repository branch, master, updated. openafs-devel-1_9_0-56-gde3e728

[Gerrit Code Review]

The following commit has been merged in the master branch:
commit de3e7289e227db057cb4eca431e47d5c5502da53
Author: Mark Vitale <mvitale@sinenomine.net>
Date:   Thu Nov 5 18:16:51 2020 -0500

    vos: avoid double release of a volume lock
    
    To update a volume entry in the VLDB, vos commands typically lock the
    volume entry via VL_SetLock, then call VL_UpdateEntryN, then release the
    lock via VL_ReleaseLock.  However, some vos commands exploit the
    optional lock release flags of VL_UpdateEntryN to combine the update and
    unlock operations into a single RPC.  This approach requires extra care
    to ensure that VL_ReleaseLock is issued for a failed VL_UpdateEntryN,
    but NOT for a successful VL_UpdateEntryN.
    
    Unfortunately, the following commands have success paths that fall
    through to the error path, resulting in a double release of the volume
    lock:
     - vos convertROtoRW
     - vos release
    
    A second VL_ReleaseLock of a volume entry that has already been unlocked
    via VL_UpdateEntryN is essentially a harmless no-op (other than negating
    any benefit of exploiting the VL_UpdateEntryN lock flags).  However, if
    there is a race with another volume operation on the same volume, it is
    possible for this bug to release the volume lock of a different volume
    operation.
    
    This problem has been present in 'vos release' since OpenAFS 1.0.  This
    problem has been present in 'vos convertROtoRW' since the command's
    introduction in commit 8af8241e94284522feb77d75aee8ea3deb73f3cc
    vol-ro-to-rw-tool-20030314.
    
    Properly maintain state to avoid unlocking a volume (with
    VL_ReleaseLock) that has already been unlocked (via VL_UpdateEntryN).
    
    Thanks to Andrew Deason for discovering the issue and suggesting the
    fix.
    
    Change-Id: I757b4619b9431d1ca980f755349806993add14a5
    Reviewed-on: https://gerrit.openafs.org/14426
    Tested-by: BuildBot <buildbot@rampaginggeek.com>
    Reviewed-by: Andrew Deason <adeason@sinenomine.net>
    Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>

 src/volser/vsprocs.c |   19 +++++++++++++------
 1 files changed, 13 insertions(+), 6 deletions(-)

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