Avoid race condition between "GRANT role" and "DROP ROLE".
Concurrently dropping either the granted role or the grantee
does not stop GRANT from completing, instead resulting in a
dangling role reference in pg_auth_members. That's relatively
harmless in the short run, but inconsistent catalog entries
are not a good thing.
This patch solves the problem by adding the granted and grantee
roles as explicit shared dependencies of the pg_auth_members entry.
That's a bit indirect, but it works because the pg_shdepend code
applies the necessary locking and rechecking.
Commit 6566133c5 previously established similar handling for
the grantor column of pg_auth_members; it's not clear why it
didn't cover the other two role OID columns.
A side-effect of this approach is that DROP OWNED BY will now drop
pg_auth_members entries that mention the target role as either the
granted or grantee role. That's clearly appropriate for the
grantee, since we'll drop its other privileges too. It doesn't
seem too far out of line for the granted role, since we're
presumably about to drop it and besides we're removing all reasons
why it'd matter to be a member of it. (One could argue that this
makes DropRole's code to auto-drop pg_auth_members entries
unnecessary, but I chose to leave it in place since perhaps some
people's workflows expect that to work without a DROP OWNED BY.)
Note to patch readers: CreateRole's first CommandCounterIncrement
call is now unconditional, because this change creates another
case in which it's needed, and it seemed to be more trouble than
it's worth to preserve that micro-optimization.
Arguably this is a bug fix, but the fact that it changes the
expected contents of pg_shdepend seems like not a great thing
to do in the stable branches, and perhaps we don't want the
change in DROP OWNED BY semantics there either. On the other
hand, I opted not to force a catversion bump in HEAD, because
the presence or absence of these entries doesn't matter for
most purposes.
Reported-by: Virender Singla <virender.cse@gmail.com>
Reviewed-by: Laurenz Albe <laurenz.albe@cybertec.at>
Discussion: https://postgr.es/m/CAM6Zo8woa62ZFHtMKox6a4jb8qQ=w87R2L0K8347iE-juQL2EA@mail.gmail.com
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/98fc31d6499163a0a781aa6f13582a07f09cd7c6
Modified Files
--------------
doc/src/sgml/ref/drop_owned.sgml | 2 +-
src/backend/commands/user.c | 23 +++++++++++++++++------
src/test/regress/expected/privileges.out | 30 ++++++++++++++++++++++++++++++
src/test/regress/sql/privileges.sql | 15 +++++++++++++++
4 files changed, 63 insertions(+), 7 deletions(-)
