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Commitc9f4618

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Add defenses against running with a wrong selection of LOBLKSIZE.
It's critical that the backend's idea of LOBLKSIZE match the way data hasactually been divided up in pg_largeobject. While we don't provide anydirect way to adjust that value, doing so is a one-line source code changeand various people have expressed interest recently in changing it. So,just as with TOAST_MAX_CHUNK_SIZE, it seems prudent to record the value inpg_control and cross-check that the backend's compiled-in setting matchesthe on-disk data.Also tweak the code in inv_api.c so that fetches from pg_largeobjectexplicitly verify that the length of the data field is not more thanLOBLKSIZE. Formerly we just had Asserts() for that, which is no protectionat all in production builds. In some of the call sites an overlength datavalue would translate directly to a security-relevant stack clobber, so itseems worth one extra runtime comparison to be sure.In the back branches, we can't change the contents of pg_control; but wecan still make the extra checks in inv_api.c, which will offer some amountof protection against running with the wrong value of LOBLKSIZE.
1 parent037c6fb commitc9f4618

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+39
-45
lines changed

1 file changed

+39
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lines changed

‎src/backend/storage/large_object/inv_api.c

Lines changed: 39 additions & 45 deletions
Original file line numberDiff line numberDiff line change
@@ -174,13 +174,38 @@ myLargeObjectExists(Oid loid, Snapshot snapshot)
174174
}
175175

176176

177-
staticint32
178-
getbytealen(bytea*data)
177+
/*
178+
* Extract data field from a pg_largeobject tuple, detoasting if needed
179+
* and verifying that the length is sane. Returns data pointer (a bytea *),
180+
* data length, and an indication of whether to pfree the data pointer.
181+
*/
182+
staticvoid
183+
getdatafield(Form_pg_largeobjecttuple,
184+
bytea**pdatafield,
185+
int*plen,
186+
bool*pfreeit)
179187
{
180-
Assert(!VARATT_IS_EXTENDED(data));
181-
if (VARSIZE(data)<VARHDRSZ)
182-
elog(ERROR,"invalid VARSIZE(data)");
183-
return (VARSIZE(data)-VARHDRSZ);
188+
bytea*datafield;
189+
intlen;
190+
boolfreeit;
191+
192+
datafield=&(tuple->data);/* see note at top of file */
193+
freeit= false;
194+
if (VARATT_IS_EXTENDED(datafield))
195+
{
196+
datafield= (bytea*)
197+
heap_tuple_untoast_attr((structvarlena*)datafield);
198+
freeit= true;
199+
}
200+
len=VARSIZE(datafield)-VARHDRSZ;
201+
if (len<0||len>LOBLKSIZE)
202+
ereport(ERROR,
203+
(errcode(ERRCODE_DATA_CORRUPTED),
204+
errmsg("pg_largeobject entry for OID %u, page %d has invalid data field size %d",
205+
tuple->loid,tuple->pageno,len)));
206+
*pdatafield=datafield;
207+
*plen=len;
208+
*pfreeit=freeit;
184209
}
185210

186211

@@ -362,20 +387,14 @@ inv_getsize(LargeObjectDesc *obj_desc)
362387
{
363388
Form_pg_largeobjectdata;
364389
bytea*datafield;
390+
intlen;
365391
boolpfreeit;
366392

367393
if (HeapTupleHasNulls(tuple))/* paranoia */
368394
elog(ERROR,"null field found in pg_largeobject");
369395
data= (Form_pg_largeobject)GETSTRUCT(tuple);
370-
datafield=&(data->data);/* see note at top of file */
371-
pfreeit= false;
372-
if (VARATT_IS_EXTENDED(datafield))
373-
{
374-
datafield= (bytea*)
375-
heap_tuple_untoast_attr((structvarlena*)datafield);
376-
pfreeit= true;
377-
}
378-
lastbyte=data->pageno*LOBLKSIZE+getbytealen(datafield);
396+
getdatafield(data,&datafield,&len,&pfreeit);
397+
lastbyte=data->pageno*LOBLKSIZE+len;
379398
if (pfreeit)
380399
pfree(datafield);
381400
}
@@ -490,15 +509,7 @@ inv_read(LargeObjectDesc *obj_desc, char *buf, int nbytes)
490509
off= (int) (obj_desc->offset-pageoff);
491510
Assert(off >=0&&off<LOBLKSIZE);
492511

493-
datafield=&(data->data);/* see note at top of file */
494-
pfreeit= false;
495-
if (VARATT_IS_EXTENDED(datafield))
496-
{
497-
datafield= (bytea*)
498-
heap_tuple_untoast_attr((structvarlena*)datafield);
499-
pfreeit= true;
500-
}
501-
len=getbytealen(datafield);
512+
getdatafield(data,&datafield,&len,&pfreeit);
502513
if (len>off)
503514
{
504515
n=len-off;
@@ -617,16 +628,7 @@ inv_write(LargeObjectDesc *obj_desc, const char *buf, int nbytes)
617628
*
618629
* First, load old data into workbuf
619630
*/
620-
datafield=&(olddata->data);/* see note at top of file */
621-
pfreeit= false;
622-
if (VARATT_IS_EXTENDED(datafield))
623-
{
624-
datafield= (bytea*)
625-
heap_tuple_untoast_attr((structvarlena*)datafield);
626-
pfreeit= true;
627-
}
628-
len=getbytealen(datafield);
629-
Assert(len <=LOBLKSIZE);
631+
getdatafield(olddata,&datafield,&len,&pfreeit);
630632
memcpy(workb,VARDATA(datafield),len);
631633
if (pfreeit)
632634
pfree(datafield);
@@ -799,19 +801,11 @@ inv_truncate(LargeObjectDesc *obj_desc, int len)
799801
if (olddata!=NULL&&olddata->pageno==pageno)
800802
{
801803
/* First, load old data into workbuf */
802-
bytea*datafield=&(olddata->data);/* see note at top of
803-
* file */
804-
boolpfreeit= false;
804+
bytea*datafield;
805805
intpagelen;
806+
boolpfreeit;
806807

807-
if (VARATT_IS_EXTENDED(datafield))
808-
{
809-
datafield= (bytea*)
810-
heap_tuple_untoast_attr((structvarlena*)datafield);
811-
pfreeit= true;
812-
}
813-
pagelen=getbytealen(datafield);
814-
Assert(pagelen <=LOBLKSIZE);
808+
getdatafield(olddata,&datafield,&pagelen,&pfreeit);
815809
memcpy(workb,VARDATA(datafield),pagelen);
816810
if (pfreeit)
817811
pfree(datafield);

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