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Commitf841ceb

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Improve TRUNCATE by avoiding early lock queue
A caller of TRUNCATE could previously queue for an access exclusive lockon a relation it may not have permission to truncate, potentiallyinterfering with users authorized to work on it. This can be veryintrusive depending on the lock attempted to be taken. For example,pg_authid could be blocked, preventing any authentication attempt tohappen on a PostgreSQL instance.This commit fixes the case of TRUNCATE so as RangeVarGetRelidExtended isused with a callback doing the necessary ACL checks at an earlier stage,avoiding lock queuing issues, so as an immediate failure happens forunprivileged users instead of waiting on a lock that would not betaken.This is rather similar to the type of work done incbe24a6 for CLUSTER,and the code of TRUNCATE is this time refactored so as there is nouser-facing changes. As the commit for CLUSTER, no back-patch is done.Reported-by: Lloyd Albin, Jeremy SchneiderAuthor: Michael PaquierReviewed by: Nathan Bossart, Kyotaro HoriguchiDiscussion:https://postgr.es/m/152512087100.19803.12733865831237526317@wrigleys.postgresql.orgDiscussion:https://postgr.es/m/20180806165816.GA19883@paquier.xyz
1 parent2b13702 commitf841ceb

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4 files changed

+204
-18
lines changed

4 files changed

+204
-18
lines changed

‎src/backend/commands/tablecmds.c

Lines changed: 66 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -300,7 +300,10 @@ struct DropRelationCallbackState
300300
#definechild_dependency_type(child_is_partition)\
301301
((child_is_partition) ? DEPENDENCY_AUTO : DEPENDENCY_NORMAL)
302302

303-
staticvoidtruncate_check_rel(Relationrel);
303+
staticvoidtruncate_check_rel(Oidrelid,Form_pg_classreltuple);
304+
staticvoidtruncate_check_activity(Relationrel);
305+
staticvoidRangeVarCallbackForTruncate(constRangeVar*relation,
306+
OidrelId,OidoldRelId,void*arg);
304307
staticList*MergeAttributes(List*schema,List*supers,charrelpersistence,
305308
boolis_partition,List**supOids,List**supconstr,
306309
int*supOidCount);
@@ -1336,15 +1339,26 @@ ExecuteTruncate(TruncateStmt *stmt)
13361339
boolrecurse=rv->inh;
13371340
Oidmyrelid;
13381341

1339-
rel=heap_openrv(rv,AccessExclusiveLock);
1340-
myrelid=RelationGetRelid(rel);
1342+
myrelid=RangeVarGetRelidExtended(rv,AccessExclusiveLock,
1343+
0,RangeVarCallbackForTruncate,
1344+
NULL);
1345+
1346+
/* open the relation, we already hold a lock on it */
1347+
rel=heap_open(myrelid,NoLock);
1348+
13411349
/* don't throw error for "TRUNCATE foo, foo" */
13421350
if (list_member_oid(relids,myrelid))
13431351
{
13441352
heap_close(rel,AccessExclusiveLock);
13451353
continue;
13461354
}
1347-
truncate_check_rel(rel);
1355+
1356+
/*
1357+
* RangeVarGetRelidExtended() has done most checks with its callback,
1358+
* but other checks with the now-opened Relation remain.
1359+
*/
1360+
truncate_check_activity(rel);
1361+
13481362
rels=lappend(rels,rel);
13491363
relids=lappend_oid(relids,myrelid);
13501364
/* Log this relation only if needed for logical decoding */
@@ -1367,7 +1381,9 @@ ExecuteTruncate(TruncateStmt *stmt)
13671381

13681382
/* find_all_inheritors already got lock */
13691383
rel=heap_open(childrelid,NoLock);
1370-
truncate_check_rel(rel);
1384+
truncate_check_rel(RelationGetRelid(rel),rel->rd_rel);
1385+
truncate_check_activity(rel);
1386+
13711387
rels=lappend(rels,rel);
13721388
relids=lappend_oid(relids,childrelid);
13731389
/* Log this relation only if needed for logical decoding */
@@ -1450,7 +1466,8 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
14501466
ereport(NOTICE,
14511467
(errmsg("truncate cascades to table \"%s\"",
14521468
RelationGetRelationName(rel))));
1453-
truncate_check_rel(rel);
1469+
truncate_check_rel(relid,rel->rd_rel);
1470+
truncate_check_activity(rel);
14541471
rels=lappend(rels,rel);
14551472
relids=lappend_oid(relids,relid);
14561473
/* Log this relation only if needed for logical decoding */
@@ -1700,38 +1717,47 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
17001717
}
17011718

17021719
/*
1703-
* Check that a given rel is safe to truncate. Subroutine for ExecuteTruncate
1720+
* Check that a given relation is safe to truncate. Subroutine for
1721+
* ExecuteTruncate() and RangeVarCallbackForTruncate().
17041722
*/
17051723
staticvoid
1706-
truncate_check_rel(Relationrel)
1724+
truncate_check_rel(Oidrelid,Form_pg_classreltuple)
17071725
{
17081726
AclResultaclresult;
1727+
char*relname=NameStr(reltuple->relname);
17091728

17101729
/*
17111730
* Only allow truncate on regular tables and partitioned tables (although,
17121731
* the latter are only being included here for the following checks; no
17131732
* physical truncation will occur in their case.)
17141733
*/
1715-
if (rel->rd_rel->relkind!=RELKIND_RELATION&&
1716-
rel->rd_rel->relkind!=RELKIND_PARTITIONED_TABLE)
1734+
if (reltuple->relkind!=RELKIND_RELATION&&
1735+
reltuple->relkind!=RELKIND_PARTITIONED_TABLE)
17171736
ereport(ERROR,
17181737
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
1719-
errmsg("\"%s\" is not a table",
1720-
RelationGetRelationName(rel))));
1738+
errmsg("\"%s\" is not a table",relname)));
17211739

17221740
/* Permissions checks */
1723-
aclresult=pg_class_aclcheck(RelationGetRelid(rel),GetUserId(),
1724-
ACL_TRUNCATE);
1741+
aclresult=pg_class_aclcheck(relid,GetUserId(),ACL_TRUNCATE);
17251742
if (aclresult!=ACLCHECK_OK)
1726-
aclcheck_error(aclresult,get_relkind_objtype(rel->rd_rel->relkind),
1727-
RelationGetRelationName(rel));
1743+
aclcheck_error(aclresult,get_relkind_objtype(reltuple->relkind),
1744+
relname);
17281745

1729-
if (!allowSystemTableMods&&IsSystemRelation(rel))
1746+
if (!allowSystemTableMods&&IsSystemClass(relid,reltuple))
17301747
ereport(ERROR,
17311748
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
17321749
errmsg("permission denied: \"%s\" is a system catalog",
1733-
RelationGetRelationName(rel))));
1750+
relname)));
1751+
}
17341752

1753+
/*
1754+
* Set of extra sanity checks to check if a given relation is safe to
1755+
* truncate. This is split with truncate_check_rel() as
1756+
* RangeVarCallbackForTruncate() cannot open a Relation yet.
1757+
*/
1758+
staticvoid
1759+
truncate_check_activity(Relationrel)
1760+
{
17351761
/*
17361762
* Don't allow truncate on temp tables of other backends ... their local
17371763
* buffer manager is not going to cope.
@@ -13419,6 +13445,28 @@ RangeVarCallbackOwnsTable(const RangeVar *relation,
1341913445
aclcheck_error(ACLCHECK_NOT_OWNER,get_relkind_objtype(get_rel_relkind(relId)),relation->relname);
1342013446
}
1342113447

13448+
/*
13449+
* Callback to RangeVarGetRelidExtended() for TRUNCATE processing.
13450+
*/
13451+
staticvoid
13452+
RangeVarCallbackForTruncate(constRangeVar*relation,
13453+
OidrelId,OidoldRelId,void*arg)
13454+
{
13455+
HeapTupletuple;
13456+
13457+
/* Nothing to do if the relation was not found. */
13458+
if (!OidIsValid(relId))
13459+
return;
13460+
13461+
tuple=SearchSysCache1(RELOID,ObjectIdGetDatum(relId));
13462+
if (!HeapTupleIsValid(tuple))/* should not happen */
13463+
elog(ERROR,"cache lookup failed for relation %u",relId);
13464+
13465+
truncate_check_rel(relId, (Form_pg_class)GETSTRUCT(tuple));
13466+
13467+
ReleaseSysCache(tuple);
13468+
}
13469+
1342213470
/*
1342313471
* Callback to RangeVarGetRelidExtended(), similar to
1342413472
* RangeVarCallbackOwnsTable() but without checks on the type of the relation.
Lines changed: 99 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,99 @@
1+
Parsed test spec with 2 sessions
2+
3+
starting permutation: s1_begin s1_tab_lookup s2_auth s2_truncate s1_commit s2_reset
4+
step s1_begin: BEGIN;
5+
step s1_tab_lookup: SELECT count(*) >= 0 FROM truncate_tab;
6+
?column?
7+
8+
t
9+
step s2_auth: SET ROLE regress_truncate_conflict;
10+
step s2_truncate: TRUNCATE truncate_tab;
11+
ERROR: permission denied for table truncate_tab
12+
step s1_commit: COMMIT;
13+
step s2_reset: RESET ROLE;
14+
15+
starting permutation: s1_begin s2_auth s2_truncate s1_tab_lookup s1_commit s2_reset
16+
step s1_begin: BEGIN;
17+
step s2_auth: SET ROLE regress_truncate_conflict;
18+
step s2_truncate: TRUNCATE truncate_tab;
19+
ERROR: permission denied for table truncate_tab
20+
step s1_tab_lookup: SELECT count(*) >= 0 FROM truncate_tab;
21+
?column?
22+
23+
t
24+
step s1_commit: COMMIT;
25+
step s2_reset: RESET ROLE;
26+
27+
starting permutation: s1_begin s2_auth s1_tab_lookup s2_truncate s1_commit s2_reset
28+
step s1_begin: BEGIN;
29+
step s2_auth: SET ROLE regress_truncate_conflict;
30+
step s1_tab_lookup: SELECT count(*) >= 0 FROM truncate_tab;
31+
?column?
32+
33+
t
34+
step s2_truncate: TRUNCATE truncate_tab;
35+
ERROR: permission denied for table truncate_tab
36+
step s1_commit: COMMIT;
37+
step s2_reset: RESET ROLE;
38+
39+
starting permutation: s2_auth s2_truncate s1_begin s1_tab_lookup s1_commit s2_reset
40+
step s2_auth: SET ROLE regress_truncate_conflict;
41+
step s2_truncate: TRUNCATE truncate_tab;
42+
ERROR: permission denied for table truncate_tab
43+
step s1_begin: BEGIN;
44+
step s1_tab_lookup: SELECT count(*) >= 0 FROM truncate_tab;
45+
?column?
46+
47+
t
48+
step s1_commit: COMMIT;
49+
step s2_reset: RESET ROLE;
50+
51+
starting permutation: s1_begin s1_tab_lookup s2_grant s2_auth s2_truncate s1_commit s2_reset
52+
step s1_begin: BEGIN;
53+
step s1_tab_lookup: SELECT count(*) >= 0 FROM truncate_tab;
54+
?column?
55+
56+
t
57+
step s2_grant: GRANT TRUNCATE ON truncate_tab TO regress_truncate_conflict;
58+
step s2_auth: SET ROLE regress_truncate_conflict;
59+
step s2_truncate: TRUNCATE truncate_tab; <waiting ...>
60+
step s1_commit: COMMIT;
61+
step s2_truncate: <... completed>
62+
step s2_reset: RESET ROLE;
63+
64+
starting permutation: s1_begin s2_grant s2_auth s2_truncate s1_tab_lookup s1_commit s2_reset
65+
step s1_begin: BEGIN;
66+
step s2_grant: GRANT TRUNCATE ON truncate_tab TO regress_truncate_conflict;
67+
step s2_auth: SET ROLE regress_truncate_conflict;
68+
step s2_truncate: TRUNCATE truncate_tab;
69+
step s1_tab_lookup: SELECT count(*) >= 0 FROM truncate_tab;
70+
?column?
71+
72+
t
73+
step s1_commit: COMMIT;
74+
step s2_reset: RESET ROLE;
75+
76+
starting permutation: s1_begin s2_grant s2_auth s1_tab_lookup s2_truncate s1_commit s2_reset
77+
step s1_begin: BEGIN;
78+
step s2_grant: GRANT TRUNCATE ON truncate_tab TO regress_truncate_conflict;
79+
step s2_auth: SET ROLE regress_truncate_conflict;
80+
step s1_tab_lookup: SELECT count(*) >= 0 FROM truncate_tab;
81+
?column?
82+
83+
t
84+
step s2_truncate: TRUNCATE truncate_tab; <waiting ...>
85+
step s1_commit: COMMIT;
86+
step s2_truncate: <... completed>
87+
step s2_reset: RESET ROLE;
88+
89+
starting permutation: s2_grant s2_auth s2_truncate s1_begin s1_tab_lookup s1_commit s2_reset
90+
step s2_grant: GRANT TRUNCATE ON truncate_tab TO regress_truncate_conflict;
91+
step s2_auth: SET ROLE regress_truncate_conflict;
92+
step s2_truncate: TRUNCATE truncate_tab;
93+
step s1_begin: BEGIN;
94+
step s1_tab_lookup: SELECT count(*) >= 0 FROM truncate_tab;
95+
?column?
96+
97+
t
98+
step s1_commit: COMMIT;
99+
step s2_reset: RESET ROLE;

‎src/test/isolation/isolation_schedule

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -76,3 +76,4 @@ test: partition-key-update-2
7676
test: partition-key-update-3
7777
test: partition-key-update-4
7878
test: plpgsql-toast
79+
test: truncate-conflict
Lines changed: 38 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,38 @@
1+
# Tests for locking conflicts with TRUNCATE commands.
2+
3+
setup
4+
{
5+
CREATEROLEregress_truncate_conflict;
6+
CREATETABLEtruncate_tab (aint);
7+
}
8+
9+
teardown
10+
{
11+
DROPTABLEtruncate_tab;
12+
DROPROLEregress_truncate_conflict;
13+
}
14+
15+
session"s1"
16+
step"s1_begin" {BEGIN; }
17+
step"s1_tab_lookup" {SELECTcount(*)>=0FROMtruncate_tab; }
18+
step"s1_commit" {COMMIT; }
19+
20+
session"s2"
21+
step"s2_grant" {GRANTTRUNCATEONtruncate_tabTOregress_truncate_conflict; }
22+
step"s2_auth" {SETROLEregress_truncate_conflict; }
23+
step"s2_truncate" {TRUNCATEtruncate_tab; }
24+
step"s2_reset" {RESETROLE; }
25+
26+
# The role doesn't have privileges to truncate the table, so TRUNCATE should
27+
# immediately fail without waiting for a lock.
28+
permutation"s1_begin""s1_tab_lookup""s2_auth""s2_truncate""s1_commit""s2_reset"
29+
permutation"s1_begin""s2_auth""s2_truncate""s1_tab_lookup""s1_commit""s2_reset"
30+
permutation"s1_begin""s2_auth""s1_tab_lookup""s2_truncate""s1_commit""s2_reset"
31+
permutation"s2_auth""s2_truncate""s1_begin""s1_tab_lookup""s1_commit""s2_reset"
32+
33+
# The role has privileges to truncate the table, TRUNCATE will block if
34+
# another session holds a lock on the table and succeed in all cases.
35+
permutation"s1_begin""s1_tab_lookup""s2_grant""s2_auth""s2_truncate""s1_commit""s2_reset"
36+
permutation"s1_begin""s2_grant""s2_auth""s2_truncate""s1_tab_lookup""s1_commit""s2_reset"
37+
permutation"s1_begin""s2_grant""s2_auth""s1_tab_lookup""s2_truncate""s1_commit""s2_reset"
38+
permutation"s2_grant""s2_auth""s2_truncate""s1_begin""s1_tab_lookup""s1_commit""s2_reset"

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