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Commitd3c9f9c

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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 parent6bf6e52 commitd3c9f9c

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+39
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lines changed

1 file changed

+39
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‎src/backend/storage/large_object/inv_api.c

Lines changed: 39 additions & 45 deletions
Original file line numberDiff line numberDiff line change
@@ -175,13 +175,38 @@ myLargeObjectExists(Oid loid, Snapshot snapshot)
175175
}
176176

177177

178-
staticint32
179-
getbytealen(bytea*data)
178+
/*
179+
* Extract data field from a pg_largeobject tuple, detoasting if needed
180+
* and verifying that the length is sane. Returns data pointer (a bytea *),
181+
* data length, and an indication of whether to pfree the data pointer.
182+
*/
183+
staticvoid
184+
getdatafield(Form_pg_largeobjecttuple,
185+
bytea**pdatafield,
186+
int*plen,
187+
bool*pfreeit)
180188
{
181-
Assert(!VARATT_IS_EXTENDED(data));
182-
if (VARSIZE(data)<VARHDRSZ)
183-
elog(ERROR,"invalid VARSIZE(data)");
184-
return (VARSIZE(data)-VARHDRSZ);
189+
bytea*datafield;
190+
intlen;
191+
boolfreeit;
192+
193+
datafield=&(tuple->data);/* see note at top of file */
194+
freeit= false;
195+
if (VARATT_IS_EXTENDED(datafield))
196+
{
197+
datafield= (bytea*)
198+
heap_tuple_untoast_attr((structvarlena*)datafield);
199+
freeit= true;
200+
}
201+
len=VARSIZE(datafield)-VARHDRSZ;
202+
if (len<0||len>LOBLKSIZE)
203+
ereport(ERROR,
204+
(errcode(ERRCODE_DATA_CORRUPTED),
205+
errmsg("pg_largeobject entry for OID %u, page %d has invalid data field size %d",
206+
tuple->loid,tuple->pageno,len)));
207+
*pdatafield=datafield;
208+
*plen=len;
209+
*pfreeit=freeit;
185210
}
186211

187212

@@ -367,20 +392,14 @@ inv_getsize(LargeObjectDesc *obj_desc)
367392
{
368393
Form_pg_largeobjectdata;
369394
bytea*datafield;
395+
intlen;
370396
boolpfreeit;
371397

372398
if (HeapTupleHasNulls(tuple))/* paranoia */
373399
elog(ERROR,"null field found in pg_largeobject");
374400
data= (Form_pg_largeobject)GETSTRUCT(tuple);
375-
datafield=&(data->data);/* see note at top of file */
376-
pfreeit= false;
377-
if (VARATT_IS_EXTENDED(datafield))
378-
{
379-
datafield= (bytea*)
380-
heap_tuple_untoast_attr((structvarlena*)datafield);
381-
pfreeit= true;
382-
}
383-
lastbyte=data->pageno*LOBLKSIZE+getbytealen(datafield);
401+
getdatafield(data,&datafield,&len,&pfreeit);
402+
lastbyte=data->pageno*LOBLKSIZE+len;
384403
if (pfreeit)
385404
pfree(datafield);
386405
}
@@ -495,15 +514,7 @@ inv_read(LargeObjectDesc *obj_desc, char *buf, int nbytes)
495514
off= (int) (obj_desc->offset-pageoff);
496515
Assert(off >=0&&off<LOBLKSIZE);
497516

498-
datafield=&(data->data);/* see note at top of file */
499-
pfreeit= false;
500-
if (VARATT_IS_EXTENDED(datafield))
501-
{
502-
datafield= (bytea*)
503-
heap_tuple_untoast_attr((structvarlena*)datafield);
504-
pfreeit= true;
505-
}
506-
len=getbytealen(datafield);
517+
getdatafield(data,&datafield,&len,&pfreeit);
507518
if (len>off)
508519
{
509520
n=len-off;
@@ -622,16 +633,7 @@ inv_write(LargeObjectDesc *obj_desc, const char *buf, int nbytes)
622633
*
623634
* First, load old data into workbuf
624635
*/
625-
datafield=&(olddata->data);/* see note at top of file */
626-
pfreeit= false;
627-
if (VARATT_IS_EXTENDED(datafield))
628-
{
629-
datafield= (bytea*)
630-
heap_tuple_untoast_attr((structvarlena*)datafield);
631-
pfreeit= true;
632-
}
633-
len=getbytealen(datafield);
634-
Assert(len <=LOBLKSIZE);
636+
getdatafield(olddata,&datafield,&len,&pfreeit);
635637
memcpy(workb,VARDATA(datafield),len);
636638
if (pfreeit)
637639
pfree(datafield);
@@ -807,19 +809,11 @@ inv_truncate(LargeObjectDesc *obj_desc, int len)
807809
if (olddata!=NULL&&olddata->pageno==pageno)
808810
{
809811
/* First, load old data into workbuf */
810-
bytea*datafield=&(olddata->data);/* see note at top of
811-
* file */
812-
boolpfreeit= false;
812+
bytea*datafield;
813813
intpagelen;
814+
boolpfreeit;
814815

815-
if (VARATT_IS_EXTENDED(datafield))
816-
{
817-
datafield= (bytea*)
818-
heap_tuple_untoast_attr((structvarlena*)datafield);
819-
pfreeit= true;
820-
}
821-
pagelen=getbytealen(datafield);
822-
Assert(pagelen <=LOBLKSIZE);
816+
getdatafield(olddata,&datafield,&pagelen,&pfreeit);
823817
memcpy(workb,VARDATA(datafield),pagelen);
824818
if (pfreeit)
825819
pfree(datafield);

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