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help / color / mirror / Atom feedFrom: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
To: n.kalinin@postgrespro.ru
To: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #19476: Segmentation fault in contrib/spi
Date: Tue, 12 May 2026 23:34:21 +0530
Message-ID: <CAJTYsWVuNPbqS2p1gEitRLBHuytqM7OMawuzVH6g4uqGw4RBsQ@mail.gmail.com> (raw)
In-Reply-To: <19476-bd04ea6241345303@postgresql.org>
References: <19476-bd04ea6241345303@postgresql.org>
Hi,
On Tue, 12 May 2026 at 21:14, PG Bug reporting form <noreply@postgresql.org>
wrote:
>
> CREATE EXTENSION refint;
> CREATE TABLE c (id int4);
> CREATE UNIQUE INDEX ci ON c(id);
> CREATE TABLE b (refb int4);
> CREATE INDEX bi ON b(refb);
>
> CREATE TRIGGER at AFTER DELETE OR UPDATE ON c FOR EACH ROW
> EXECUTE FUNCTION check_foreign_key (1, 'cascade', 'id', 'b', 'refb');
>
> CREATE TRIGGER bt AFTER INSERT OR UPDATE ON b FOR EACH ROW
> EXECUTE FUNCTION check_primary_key ('refb', 'c', 'id');
>
> INSERT INTO c VALUES (10);
> INSERT INTO b VALUES (10);
> UPDATE c SET id = NULL WHERE id = 10;
>
> Backtrace:
> #0 __strlen_avx2 () at ../sysdeps/x86_64/multiarch/strlen-avx2.S:76
> #1 0x0000563a92ca096e in quote_literal_cstr (rawstr=0x0) at quote.c:109
> #2 0x00007fa4a7cce5f8 in check_foreign_key (fcinfo=<optimized out>) at
> refint.c:489
> #3 0x0000563a929c1d52 in ExecCallTriggerFunc
> (trigdata=trigdata@entry=0x7fff8cae1100,
> tgindx=tgindx@entry=0, finfo=finfo@entry=0x563aa5ae4438,
> instr=instr@entry=0x0,
> per_tuple_context=per_tuple_context@entry=0x563aa5adb9c0) at
> trigger.c:2369
> #4 0x0000563a929c4110 in AfterTriggerExecute (estate=<optimized out>,
> event=0x563aa5aedbb0,
> relInfo=0x563aa5ae4068, src_relInfo=<optimized out>,
> dst_relInfo=<optimized out>,
> trigdesc=0x563aa5ae4278, finfo=0x563aa5ae4438, instr=0x0,
> per_tuple_context=<optimized out>, trig_tuple_slot1=0x0,
> trig_tuple_slot2=0x0)
> at trigger.c:4559
> #5 afterTriggerInvokeEvents (events=events@entry=0x563aa5a75050,
> firing_id=1,
> estate=estate@entry=0x563aa5ae3b20, delete_ok=delete_ok@entry=false)
> at
> trigger.c:4800
> #6 0x0000563a929c8e88 in AfterTriggerEndQuery
> (estate=estate@entry=0x563aa5ae3b20)
> at trigger.c:5182
> #7 0x0000563a929ed504 in standard_ExecutorFinish
> (queryDesc=0x563aa5996e20)
> at execMain.c:443
> #8 0x0000563a92bd96f8 in ProcessQuery (plan=0x563aa5af4168,
> sourceText=0x563aa59df7e0 "UPDATE c SET id = NULL WHERE id = 10;",
> params=0x0,
> queryEnv=0x0, dest=0x563aa5aeae28, qc=0x7fff8cae1460) at pquery.c:194
> #9 0x0000563a92bda41e in PortalRunMulti
> (portal=portal@entry=0x563aa5a60510,
> isTopLevel=isTopLevel@entry=true,
> setHoldSnapshot=setHoldSnapshot@entry=false,
> --Type <RET> for more, q to quit, c to continue without paging--c
> dest=dest@entry=0x563aa5aeae28, altdest=altdest@entry=0x563aa5aeae28,
> qc=qc@entry=0x7fff8cae1460) at pquery.c:1272
> #10 0x0000563a92bda7f7 in PortalRun (portal=portal@entry=0x563aa5a60510,
> count=count@entry=9223372036854775807, isTopLevel=isTopLevel@entry
> =true,
> dest=dest@entry=0x563aa5aeae28, altdest=altdest@entry=0x563aa5aeae28,
> qc=qc@entry=0x7fff8cae1460) at pquery.c:788
> #11 0x0000563a92bd63fa in exec_simple_query (
> query_string=0x563aa59df7e0 "UPDATE c SET id = NULL WHERE id = 10;") at
> postgres.c:1274
> #12 0x0000563a92bd7fc5 in PostgresMain (dbname=<optimized out>,
> username=<optimized out>)
> at postgres.c:4770
> #13 0x0000563a92bd23bd in BackendMain (startup_data=<optimized out>,
> startup_data_len=<optimized out>) at backend_startup.c:124
> #14 0x0000563a92b24932 in postmaster_child_launch (child_type=<optimized
> out>, child_slot=1,
> startup_data=startup_data@entry=0x7fff8cae1900,
> startup_data_len=startup_data_len@entry=24,
> client_sock=client_sock@entry=0x7fff8cae1920)
> at launch_backend.c:290
> #15 0x0000563a92b283d2 in BackendStartup (client_sock=0x7fff8cae1920) at
> postmaster.c:3569
> #16 ServerLoop () at postmaster.c:1703
> #17 0x0000563a92b29ea6 in PostmasterMain (argc=argc@entry=3,
> argv=argv@entry=0x563aa5985bf0)
> at postmaster.c:1401
> #18 0x0000563a92800a5a in main (argc=3, argv=0x563aa5985bf0) at main.c:227
>
Thanks for the report and the clear backtrace.
I had a look at this and I think the immediate crash comes from
check_foreign_key()'s cascade-update branch in contrib/spi/refint.c,
which calls SPI_getvalue() for the new key value and then passes the
result straight into snprintf("%s", ...):
nv = SPI_getvalue(newtuple, tupdesc, fn);
...
snprintf(sql + strlen(sql), sizeof(sql) - strlen(sql),
" %s = %s%s%s %s ",
args2[k], (is_char_type > 0) ? "'" : "",
nv, (is_char_type > 0) ? "'" : "", (k < nkeys) ? ", " : "");
For an UPDATE that sets the referenced key to NULL, SPI_getvalue()
returns NULL, so nv is NULL. On stock glibc/Postgres builds snprintf
substitutes "(null)" and SQL parses that as the NULL keyword, so the
cascade silently does the right thing. On builds with _FORTIFY_SOURCE
glibc's strlen check dereferences the NULL pointer instead, which
matches the backtrace you posted.
I am attaching a two-patch series that addresses this.
0001 is the minimal fix: emit the SQL NULL keyword when SPI_getvalue()
returns NULL, instead of passing a NULL pointer to snprintf. This is
small and targeted, and is sufficient on its own to fix the reported
crash. I did not add a regression test for 0001 because the bug only
manifests on hardened libc builds; on stock builds the bad snprintf
happens to produce a result that the SQL parser accepts.
0002 is a follow-up that I think makes sense but is not strictly
required for this bug. While looking at the cascade-update path I
noticed two pre-existing issues in the same code:
- The new key values were embedded into the prepared cascade UPDATE
query text as literals. Combined with plan caching (the cache key
only gained the operation type in 8cfbdf8f4df), the first set of
new values gets reused for every subsequent cascade UPDATE.
- Char-like new values were wrapped in single quotes without escaping,
so a value containing a single quote produced malformed SQL.
0002 switches that branch to use SPI parameters for the new key values
instead of embedding them into the SQL text. That naturally handles
NULLs via the SPI nulls array, lets a single cached plan handle later
UPDATEs with different keys, and avoids the quoting issue entirely.
It also adds a refint regression test that runs two cascade UPDATEs in
a row (one to NULL, one to a non-NULL value) which catches the cached-
plan reuse.
I'm happy with just 0001 if reviewers prefer to keep the fix minimal,
given that refint is intended mainly as a documentation example
(8cfbdf8f4df explicitly mentioned not back-patching changes here?).
Regards,
Ayush
Attachments:
[application/octet-stream] v1-0001-Fix-refint-cascade-UPDATE-crash-with-NULL-keys.patch (2.4K, 3-v1-0001-Fix-refint-cascade-UPDATE-crash-with-NULL-keys.patch)
download | inline diff:
From dd97dd1e196aa8dd0a12afb957b046d984ed491e Mon Sep 17 00:00:00 2001
From: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Date: Tue, 12 May 2026 17:43:12 +0000
Subject: [PATCH v1 1/2] Fix refint cascade UPDATE crash with NULL keys
check_foreign_key() builds cascade UPDATE queries using the new key
value retrieved by SPI_getvalue(). When that value is NULL,
SPI_getvalue() returns a NULL pointer, which the code then passed to
snprintf("%s"). That is undefined behavior; on most builds it happens
to print "(null)", which SQL then parses as the NULL keyword, but on
builds with _FORTIFY_SOURCE the snprintf formatter crashes when
computing the string length, matching the backtrace in the report.
Emit the SQL NULL keyword directly when SPI_getvalue() returns NULL.
No regression test is added because triggering the crash requires a
hardened libc; without that, the existing code already happens to
produce the correct result via the "(null)" substitution above.
Reported-by: Nikita Kalinin <n.kalinin@postgrespro.ru>
Discussion: https://postgr.es/m/19476-bd04ea6241345303@postgresql.org
---
contrib/spi/refint.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)
diff --git a/contrib/spi/refint.c b/contrib/spi/refint.c
index fbbd558ca1e..0063410f27e 100644
--- a/contrib/spi/refint.c
+++ b/contrib/spi/refint.c
@@ -496,12 +496,22 @@ check_foreign_key(PG_FUNCTION_ARGS)
#endif
/*
- * is_char_type =1 i set ' ' for define a new value
+ * is_char_type =1 i set ' ' for define a new value.
+ *
+ * SPI_getvalue() returns NULL for SQL NULL values, so
+ * emit the NULL keyword rather than passing a NULL
+ * pointer to snprintf("%s"), which is undefined
+ * behavior.
*/
- snprintf(sql + strlen(sql), sizeof(sql) - strlen(sql),
- " %s = %s%s%s %s ",
- args2[k], (is_char_type > 0) ? "'" : "",
- nv, (is_char_type > 0) ? "'" : "", (k < nkeys) ? ", " : "");
+ if (nv == NULL)
+ snprintf(sql + strlen(sql), sizeof(sql) - strlen(sql),
+ " %s = NULL %s ",
+ args2[k], (k < nkeys) ? ", " : "");
+ else
+ snprintf(sql + strlen(sql), sizeof(sql) - strlen(sql),
+ " %s = %s%s%s %s ",
+ args2[k], (is_char_type > 0) ? "'" : "",
+ nv, (is_char_type > 0) ? "'" : "", (k < nkeys) ? ", " : "");
}
strcat(sql, " where ");
}
--
2.43.0
[application/octet-stream] v1-0002-refint-parameterize-cascade-UPDATE-new-key-values.patch (9.3K, 4-v1-0002-refint-parameterize-cascade-UPDATE-new-key-values.patch)
download | inline diff:
From c4331d930e94803e180f335e0dad5f9b8a0b5717 Mon Sep 17 00:00:00 2001
From: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Date: Tue, 12 May 2026 17:53:11 +0000
Subject: [PATCH v1 2/2] refint: parameterize cascade UPDATE new key values
Previously, contrib/spi/refint's check_foreign_key() embedded the new
key values into the prepared cascade UPDATE query text as literals.
The preceding patch fixed the immediate NULL crash, but the same code
path has two other latent issues:
* Because the new values were baked into the prepared SQL, the cached
plan reused the first new key values for every subsequent UPDATE.
Adding the operation type to the plan cache key (commit 8cfbdf8f4df)
helped distinguish update vs delete, but the SET RHS was still
hard-coded into each cached plan.
* Char-like new values were wrapped in single quotes without escaping,
so a new value containing a single quote produced malformed SQL.
Switch the cascade UPDATE path to use SPI parameters for the new key
values. This naturally handles NULLs via the SPI nulls array, lets a
single cached plan handle any subsequent UPDATE, and avoids quoting
issues altogether.
Add a refint regression test that runs two cascade UPDATEs in a row to
exercise cached-plan reuse with different key values, including a NULL.
Discussion: https://postgr.es/m/19476-bd04ea6241345303@postgresql.org
---
contrib/spi/expected/refint.out | 31 +++++++++++++
contrib/spi/refint.c | 77 ++++++++++++---------------------
contrib/spi/sql/refint.sql | 28 ++++++++++++
3 files changed, 87 insertions(+), 49 deletions(-)
diff --git a/contrib/spi/expected/refint.out b/contrib/spi/expected/refint.out
index 79633603217..16b8990a80d 100644
--- a/contrib/spi/expected/refint.out
+++ b/contrib/spi/expected/refint.out
@@ -111,3 +111,34 @@ SELECT trigger_name, event_manipulation, event_object_schema, event_object_table
DROP TABLE pkeys;
DROP TABLE fkeys;
DROP TABLE fkeys2;
+-- Cascading updates should use parameters for new key values so that the
+-- cached plan can be reused for subsequent updates with different keys.
+CREATE TABLE c_null (id int4);
+CREATE UNIQUE INDEX c_null_i ON c_null(id);
+CREATE TABLE b_null (refb int4);
+CREATE INDEX b_null_i ON b_null(refb);
+CREATE TRIGGER c_null_fkey_cascade
+ after delete or update on c_null
+ for each row
+ execute function check_foreign_key (1, 'cascade', 'id', 'b_null', 'refb');
+CREATE TRIGGER b_null_pkey_exist
+ after insert or update on b_null
+ for each row
+ execute function check_primary_key ('refb', 'c_null', 'id');
+INSERT INTO c_null VALUES (10);
+INSERT INTO b_null VALUES (10);
+UPDATE c_null SET id = NULL WHERE id = 10;
+NOTICE: c_null_fkey_cascade: 1 tuple(s) of b_null are updated
+INSERT INTO c_null VALUES (20);
+INSERT INTO b_null VALUES (20);
+UPDATE c_null SET id = 30 WHERE id = 20;
+NOTICE: c_null_fkey_cascade: 1 tuple(s) of b_null are updated
+SELECT * FROM b_null ORDER BY refb NULLS FIRST;
+ refb
+------
+
+ 30
+(2 rows)
+
+DROP TABLE c_null;
+DROP TABLE b_null;
diff --git a/contrib/spi/refint.c b/contrib/spi/refint.c
index 0063410f27e..bc89015a12c 100644
--- a/contrib/spi/refint.c
+++ b/contrib/spi/refint.c
@@ -248,11 +248,12 @@ check_foreign_key(PG_FUNCTION_ARGS)
Trigger *trigger; /* to get trigger name */
int nargs; /* # of args specified in CREATE TRIGGER */
char **args; /* arguments: as described above */
- char **args_temp;
int nrefs; /* number of references (== # of plans) */
char action; /* 'R'estrict | 'S'etnull | 'C'ascade */
int nkeys; /* # of key columns */
+ int nparams; /* # of query parameters */
Datum *kvals; /* key values */
+ char *nulls = NULL; /* null markers for key values */
char *relname; /* referencing relation name */
Relation rel; /* triggered relation */
HeapTuple trigtuple = NULL; /* tuple to being changed */
@@ -343,7 +344,13 @@ check_foreign_key(PG_FUNCTION_ARGS)
* We use SPI plan preparation feature, so allocate space to place key
* values.
*/
- kvals = (Datum *) palloc(nkeys * sizeof(Datum));
+ nparams = (action == 'c' && is_update) ? 2 * nkeys : nkeys;
+ kvals = (Datum *) palloc(nparams * sizeof(Datum));
+ if (nparams > nkeys)
+ {
+ nulls = (char *) palloc(nparams * sizeof(char));
+ memset(nulls, ' ', nparams * sizeof(char));
+ }
/*
* Construct ident string as TriggerName $ TriggeredRelationId $
@@ -354,7 +361,7 @@ check_foreign_key(PG_FUNCTION_ARGS)
/* if there is no plan(s) then allocate argtypes for preparation */
if (plan->nplans <= 0)
- argtypes = (Oid *) palloc(nkeys * sizeof(Oid));
+ argtypes = (Oid *) palloc(nparams * sizeof(Oid));
/*
* else - check that we have exactly nrefs plan(s) ready
@@ -391,6 +398,9 @@ check_foreign_key(PG_FUNCTION_ARGS)
return PointerGetDatum((newtuple == NULL) ? trigtuple : newtuple);
}
+ if (plan->nplans <= 0)
+ argtypes[i] = SPI_gettypeid(tupdesc, fnumber);
+
/*
* If UPDATE then get column value from new tuple being inserted and
* compare is this the same as old one. For the moment we use string
@@ -398,6 +408,7 @@ check_foreign_key(PG_FUNCTION_ARGS)
*/
if (newtuple != NULL)
{
+ bool newisnull;
char *oldval = SPI_getvalue(trigtuple, tupdesc, fnumber);
char *newval;
@@ -408,12 +419,17 @@ check_foreign_key(PG_FUNCTION_ARGS)
newval = SPI_getvalue(newtuple, tupdesc, fnumber);
if (newval == NULL || strcmp(oldval, newval) != 0)
isequal = false;
- }
- if (plan->nplans <= 0) /* Get typeId of column */
- argtypes[i] = SPI_gettypeid(tupdesc, fnumber);
+ if (action == 'c')
+ {
+ kvals[nkeys + i] = SPI_getbinval(newtuple, tupdesc,
+ fnumber, &newisnull);
+ nulls[nkeys + i] = newisnull ? 'n' : ' ';
+ if (plan->nplans <= 0)
+ argtypes[nkeys + i] = argtypes[i];
+ }
+ }
}
- args_temp = args;
nargs -= nkeys;
args += nkeys;
@@ -468,50 +484,14 @@ check_foreign_key(PG_FUNCTION_ARGS)
{
if (is_update == 1)
{
- int fn;
- char *nv;
int k;
snprintf(sql, sizeof(sql), "update %s set ", relname);
for (k = 1; k <= nkeys; k++)
{
- int is_char_type = 0;
- char *type;
-
- fn = SPI_fnumber(tupdesc, args_temp[k - 1]);
- Assert(fn > 0); /* already checked above */
- nv = SPI_getvalue(newtuple, tupdesc, fn);
- type = SPI_gettype(tupdesc, fn);
-
- if (strcmp(type, "text") == 0 ||
- strcmp(type, "varchar") == 0 ||
- strcmp(type, "char") == 0 ||
- strcmp(type, "bpchar") == 0 ||
- strcmp(type, "date") == 0 ||
- strcmp(type, "timestamp") == 0)
- is_char_type = 1;
-#ifdef DEBUG_QUERY
- elog(DEBUG4, "check_foreign_key Debug value %s type %s %d",
- nv, type, is_char_type);
-#endif
-
- /*
- * is_char_type =1 i set ' ' for define a new value.
- *
- * SPI_getvalue() returns NULL for SQL NULL values, so
- * emit the NULL keyword rather than passing a NULL
- * pointer to snprintf("%s"), which is undefined
- * behavior.
- */
- if (nv == NULL)
- snprintf(sql + strlen(sql), sizeof(sql) - strlen(sql),
- " %s = NULL %s ",
- args2[k], (k < nkeys) ? ", " : "");
- else
- snprintf(sql + strlen(sql), sizeof(sql) - strlen(sql),
- " %s = %s%s%s %s ",
- args2[k], (is_char_type > 0) ? "'" : "",
- nv, (is_char_type > 0) ? "'" : "", (k < nkeys) ? ", " : "");
+ snprintf(sql + strlen(sql), sizeof(sql) - strlen(sql),
+ " %s = $%d %s ",
+ args2[k], nkeys + k, (k < nkeys) ? ", " : "");
}
strcat(sql, " where ");
}
@@ -546,7 +526,7 @@ check_foreign_key(PG_FUNCTION_ARGS)
}
/* Prepare plan for query */
- pplan = SPI_prepare(sql, nkeys, argtypes);
+ pplan = SPI_prepare(sql, nparams, argtypes);
if (pplan == NULL)
/* internal error */
elog(ERROR, "check_foreign_key: SPI_prepare returned %s", SPI_result_code_string(SPI_result));
@@ -591,8 +571,7 @@ check_foreign_key(PG_FUNCTION_ARGS)
relname = args[0];
- ret = SPI_execp(plan->splan[r], kvals, NULL, tcount);
- /* we have no NULLs - so we pass ^^^^ here */
+ ret = SPI_execp(plan->splan[r], kvals, nulls, tcount);
if (ret < 0)
ereport(ERROR,
diff --git a/contrib/spi/sql/refint.sql b/contrib/spi/sql/refint.sql
index 63458127917..d460ad58d53 100644
--- a/contrib/spi/sql/refint.sql
+++ b/contrib/spi/sql/refint.sql
@@ -95,3 +95,31 @@ SELECT trigger_name, event_manipulation, event_object_schema, event_object_table
DROP TABLE pkeys;
DROP TABLE fkeys;
DROP TABLE fkeys2;
+
+-- Cascading updates should use parameters for new key values so that the
+-- cached plan can be reused for subsequent updates with different keys.
+CREATE TABLE c_null (id int4);
+CREATE UNIQUE INDEX c_null_i ON c_null(id);
+CREATE TABLE b_null (refb int4);
+CREATE INDEX b_null_i ON b_null(refb);
+
+CREATE TRIGGER c_null_fkey_cascade
+ after delete or update on c_null
+ for each row
+ execute function check_foreign_key (1, 'cascade', 'id', 'b_null', 'refb');
+
+CREATE TRIGGER b_null_pkey_exist
+ after insert or update on b_null
+ for each row
+ execute function check_primary_key ('refb', 'c_null', 'id');
+
+INSERT INTO c_null VALUES (10);
+INSERT INTO b_null VALUES (10);
+UPDATE c_null SET id = NULL WHERE id = 10;
+INSERT INTO c_null VALUES (20);
+INSERT INTO b_null VALUES (20);
+UPDATE c_null SET id = 30 WHERE id = 20;
+SELECT * FROM b_null ORDER BY refb NULLS FIRST;
+
+DROP TABLE c_null;
+DROP TABLE b_null;
--
2.43.0
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To: pgsql-bugs@postgresql.org
Cc: ayushtiwari.slg01@gmail.com, n.kalinin@postgrespro.ru, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #19476: Segmentation fault in contrib/spi
In-Reply-To: <CAJTYsWVuNPbqS2p1gEitRLBHuytqM7OMawuzVH6g4uqGw4RBsQ@mail.gmail.com>
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