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Commit3985b75

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committed
Save/restore SPI's global variables in SPI_connect() and SPI_finish().
This patch removes two sources of interference between nominallyindependent functions when one SPI-using function calls another,perhaps without knowing that it does so.Chapman Flack pointed out that xml.c's query_to_xml_internal() expectsSPI_tuptable and SPI_processed to stay valid across datatype outputfunction calls; but it's possible that such a call could involvere-entrant use of SPI. It seems likely that there are similar hazardselsewhere, if not in the core code then in third-party SPI users.Previously SPI_finish() reset SPI's API globals to zeroes/nulls, whichwould typically make for a crash in such a situation. Restoring themto the values they had at SPI_connect() seems like a considerably moreuseful behavior, and it still meets the design goal of not leaving anydangling pointers to tuple tables of the function being exited.Also, cause SPI_connect() to reset these variables to zeroes/nulls aftersaving them. This prevents interference in the opposite direction: it'spossible that a SPI-using function that's only ever been tested standalonecontains assumptions that these variables start out as zeroes. That wasthe case as long as you were the outermost SPI user, but not so much foran inner user. Now it's consistent.Report and fix suggestion by Chapman Flack, actual patch by me.Back-patch to all supported branches.Discussion:https://postgr.es/m/9fa25bef-2e4f-1c32-22a4-3ad0723c4a17@anastigmatix.net
1 parentadfc156 commit3985b75

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2 files changed

+39
-9
lines changed

2 files changed

+39
-9
lines changed

‎src/backend/executor/spi.c

Lines changed: 33 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -36,10 +36,16 @@
3636
#include"utils/typcache.h"
3737

3838

39+
/*
40+
* These global variables are part of the API for various SPI functions
41+
* (a horrible API choice, but it's too late now). To reduce the risk of
42+
* interference between different SPI callers, we save and restore them
43+
* when entering/exiting a SPI nesting level.
44+
*/
3945
uint64SPI_processed=0;
4046
OidSPI_lastoid=InvalidOid;
4147
SPITupleTable*SPI_tuptable=NULL;
42-
intSPI_result;
48+
intSPI_result=0;
4349

4450
static_SPI_connection*_SPI_stack=NULL;
4551
static_SPI_connection*_SPI_current=NULL;
@@ -124,6 +130,10 @@ SPI_connect(void)
124130
_SPI_current->execCxt=NULL;
125131
_SPI_current->connectSubid=GetCurrentSubTransactionId();
126132
_SPI_current->queryEnv=NULL;
133+
_SPI_current->outer_processed=SPI_processed;
134+
_SPI_current->outer_lastoid=SPI_lastoid;
135+
_SPI_current->outer_tuptable=SPI_tuptable;
136+
_SPI_current->outer_result=SPI_result;
127137

128138
/*
129139
* Create memory contexts for this procedure
@@ -142,6 +152,15 @@ SPI_connect(void)
142152
/* ... and switch to procedure's context */
143153
_SPI_current->savedcxt=MemoryContextSwitchTo(_SPI_current->procCxt);
144154

155+
/*
156+
* Reset API global variables so that current caller cannot accidentally
157+
* depend on state of an outer caller.
158+
*/
159+
SPI_processed=0;
160+
SPI_lastoid=InvalidOid;
161+
SPI_tuptable=NULL;
162+
SPI_result=0;
163+
145164
returnSPI_OK_CONNECT;
146165
}
147166

@@ -164,12 +183,13 @@ SPI_finish(void)
164183
_SPI_current->procCxt=NULL;
165184

166185
/*
167-
*Reset result variables, especially SPI_tuptable which is probably
186+
*Restore outer API variables, especially SPI_tuptable which is probably
168187
* pointing at a just-deleted tuptable
169188
*/
170-
SPI_processed=0;
171-
SPI_lastoid=InvalidOid;
172-
SPI_tuptable=NULL;
189+
SPI_processed=_SPI_current->outer_processed;
190+
SPI_lastoid=_SPI_current->outer_lastoid;
191+
SPI_tuptable=_SPI_current->outer_tuptable;
192+
SPI_result=_SPI_current->outer_result;
173193

174194
/* Exit stack level */
175195
_SPI_connected--;
@@ -201,9 +221,11 @@ AtEOXact_SPI(bool isCommit)
201221
_SPI_current=_SPI_stack=NULL;
202222
_SPI_stack_depth=0;
203223
_SPI_connected=-1;
224+
/* Reset API global variables, too */
204225
SPI_processed=0;
205226
SPI_lastoid=InvalidOid;
206227
SPI_tuptable=NULL;
228+
SPI_result=0;
207229
}
208230

209231
/*
@@ -241,18 +263,20 @@ AtEOSubXact_SPI(bool isCommit, SubTransactionId mySubid)
241263
}
242264

243265
/*
244-
*Pop the stack entry andreset global variables. Unlike
266+
*Restore outer global variables andpop the stack entry. Unlike
245267
* SPI_finish(), we don't risk switching to memory contexts that might
246268
* be already gone.
247269
*/
270+
SPI_processed=connection->outer_processed;
271+
SPI_lastoid=connection->outer_lastoid;
272+
SPI_tuptable=connection->outer_tuptable;
273+
SPI_result=connection->outer_result;
274+
248275
_SPI_connected--;
249276
if (_SPI_connected<0)
250277
_SPI_current=NULL;
251278
else
252279
_SPI_current=&(_SPI_stack[_SPI_connected]);
253-
SPI_processed=0;
254-
SPI_lastoid=InvalidOid;
255-
SPI_tuptable=NULL;
256280
}
257281

258282
if (found&&isCommit)

‎src/include/executor/spi_priv.h

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -36,6 +36,12 @@ typedef struct
3636

3737
/* subtransaction in which current Executor call was started */
3838
SubTransactionIdexecSubid;
39+
40+
/* saved values of API global variables for previous nesting level */
41+
uint64outer_processed;
42+
Oidouter_lastoid;
43+
SPITupleTable*outer_tuptable;
44+
intouter_result;
3945
}_SPI_connection;
4046

4147
/*

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