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Commit5ac0d93

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Fix failure to zero-pad the result of bitshiftright().
If the bitstring length is not a multiple of 8, we'd shift therightmost bits into the pad space, which must be zeroes --- bit_cmp,for one, depends on that. This'd lead to the result failing tocompare equal to what it should compare equal to, as reported inbug #16013 from Daryl Waycott.This is, if memory serves, not the first such bug in the bitstringfunctions. In hopes of making it the last one, do a bit more workthan minimally necessary to fix the bug:* Add assertion checks to bit_out() and varbit_out() to complain ifthey are given incorrectly-padded input. This will improve theodds that manual testing of any new patch finds problems.* Encapsulate the padding-related logic in macros to make iteasier to use.Also, remove unnecessary padding logic from bit_or() and bitxor().Somebody had already noted that we need not re-pad the result ofbit_and() since the inputs are required to be the same length,but failed to extrapolate that to the other two.Also, move a comment block that once was near the head of varbit.c(but people kept putting other stuff in front of it), to put it inthe header block.Note for the release notes: if anyone has inconsistent data as aresult of saving the output of bitshiftright() in a table, it'spossible to fix it with something likeUPDATE mytab SET bitcol = ~(~bitcol) WHERE bitcol != ~(~bitcol);This has been broken since day one, so back-patch to all supportedbranches.Discussion:https://postgr.es/m/16013-c2765b6996aacae9@postgresql.org
1 parent0a2f894 commit5ac0d93

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4 files changed

+154
-89
lines changed

4 files changed

+154
-89
lines changed

‎src/backend/utils/adt/varbit.c

Lines changed: 77 additions & 88 deletions
Original file line numberDiff line numberDiff line change
@@ -3,6 +3,21 @@
33
* varbit.c
44
* Functions for the SQL datatypes BIT() and BIT VARYING().
55
*
6+
* The data structure contains the following elements:
7+
* header -- length of the whole data structure (incl header)
8+
* in bytes (as with all varying length datatypes)
9+
* data section -- private data section for the bits data structures
10+
* bitlength -- length of the bit string in bits
11+
* bitdata -- bit string, most significant byte first
12+
*
13+
* The length of the bitdata vector should always be exactly as many
14+
* bytes as are needed for the given bitlength. If the bitlength is
15+
* not a multiple of 8, the extra low-order padding bits of the last
16+
* byte must be zeroes.
17+
*
18+
* attypmod is defined as the length of the bit string in bits, or for
19+
* varying bits the maximum length.
20+
*
621
* Code originally contributed by Adriaan Joubert.
722
*
823
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
@@ -27,6 +42,40 @@
2742

2843
#defineHEXDIG(z) ((z)<10 ? ((z)+'0') : ((z)-10+'A'))
2944

45+
/* Mask off any bits that should be zero in the last byte of a bitstring */
46+
#defineVARBIT_PAD(vb) \
47+
do { \
48+
int32pad_ = VARBITPAD(vb); \
49+
Assert(pad_ >= 0 && pad_ < BITS_PER_BYTE); \
50+
if (pad_ > 0) \
51+
*(VARBITS(vb) + VARBITBYTES(vb) - 1) &= BITMASK << pad_; \
52+
} while (0)
53+
54+
/*
55+
* Many functions work byte-by-byte, so they have a pointer handy to the
56+
* last-plus-one byte, which saves a cycle or two.
57+
*/
58+
#defineVARBIT_PAD_LAST(vb,ptr) \
59+
do { \
60+
int32pad_ = VARBITPAD(vb); \
61+
Assert(pad_ >= 0 && pad_ < BITS_PER_BYTE); \
62+
if (pad_ > 0) \
63+
*((ptr) - 1) &= BITMASK << pad_; \
64+
} while (0)
65+
66+
/* Assert proper padding of a bitstring */
67+
#ifdefUSE_ASSERT_CHECKING
68+
#defineVARBIT_CORRECTLY_PADDED(vb) \
69+
do { \
70+
int32pad_ = VARBITPAD(vb); \
71+
Assert(pad_ >= 0 && pad_ < BITS_PER_BYTE); \
72+
Assert(pad_ == 0 || \
73+
(*(VARBITS(vb) + VARBITBYTES(vb) - 1) & ~(BITMASK << pad_)) == 0); \
74+
} while (0)
75+
#else
76+
#defineVARBIT_CORRECTLY_PADDED(vb) ((void) 0)
77+
#endif
78+
3079
staticVarBit*bit_catenate(VarBit*arg1,VarBit*arg2);
3180
staticVarBit*bitsubstring(VarBit*arg,int32s,int32l,
3281
boollength_not_specified);
@@ -87,24 +136,6 @@ anybit_typmodout(int32 typmod)
87136
}
88137

89138

90-
/*----------
91-
*attypmod -- contains the length of the bit string in bits, or for
92-
* varying bits the maximum length.
93-
*
94-
*The data structure contains the following elements:
95-
* header -- length of the whole data structure (incl header)
96-
* in bytes. (as with all varying length datatypes)
97-
* data section -- private data section for the bits data structures
98-
*bitlength -- length of the bit string in bits
99-
*bitdata -- bit string, most significant byte first
100-
*
101-
*The length of the bitdata vector should always be exactly as many
102-
*bytes as are needed for the given bitlength. If the bitlength is
103-
*not a multiple of 8, the extra low-order padding bits of the last
104-
*byte must be zeroes.
105-
*----------
106-
*/
107-
108139
/*
109140
* bit_in -
110141
* converts a char string to the internal representation of a bitstring.
@@ -264,6 +295,9 @@ bit_out(PG_FUNCTION_ARGS)
264295
len,
265296
bitlen;
266297

298+
/* Assertion to help catch any bit functions that don't pad correctly */
299+
VARBIT_CORRECTLY_PADDED(s);
300+
267301
bitlen=VARBITLEN(s);
268302
len= (bitlen+3) /4;
269303
result= (char*)palloc(len+2);
@@ -304,8 +338,6 @@ bit_recv(PG_FUNCTION_ARGS)
304338
VarBit*result;
305339
intlen,
306340
bitlen;
307-
intipad;
308-
bits8mask;
309341

310342
bitlen=pq_getmsgint(buf,sizeof(int32));
311343
if (bitlen<0||bitlen>VARBITMAXLEN)
@@ -330,13 +362,8 @@ bit_recv(PG_FUNCTION_ARGS)
330362

331363
pq_copymsgbytes(buf, (char*)VARBITS(result),VARBITBYTES(result));
332364

333-
/* Make sure last byte is zero-padded if needed */
334-
ipad=VARBITPAD(result);
335-
if (ipad>0)
336-
{
337-
mask=BITMASK <<ipad;
338-
*(VARBITS(result)+VARBITBYTES(result)-1) &=mask;
339-
}
365+
/* Make sure last byte is correctly zero-padded */
366+
VARBIT_PAD(result);
340367

341368
PG_RETURN_VARBIT_P(result);
342369
}
@@ -367,8 +394,6 @@ bit(PG_FUNCTION_ARGS)
367394
boolisExplicit=PG_GETARG_BOOL(2);
368395
VarBit*result;
369396
intrlen;
370-
intipad;
371-
bits8mask;
372397

373398
/* No work if typmod is invalid or supplied data matches it already */
374399
if (len <=0||len>VARBITMAXLEN||len==VARBITLEN(arg))
@@ -394,12 +419,7 @@ bit(PG_FUNCTION_ARGS)
394419
* if source data was shorter than target length (we assume the last byte
395420
* of the source data was itself correctly zero-padded).
396421
*/
397-
ipad=VARBITPAD(result);
398-
if (ipad>0)
399-
{
400-
mask=BITMASK <<ipad;
401-
*(VARBITS(result)+VARBITBYTES(result)-1) &=mask;
402-
}
422+
VARBIT_PAD(result);
403423

404424
PG_RETURN_VARBIT_P(result);
405425
}
@@ -574,6 +594,9 @@ varbit_out(PG_FUNCTION_ARGS)
574594
k,
575595
len;
576596

597+
/* Assertion to help catch any bit functions that don't pad correctly */
598+
VARBIT_CORRECTLY_PADDED(s);
599+
577600
len=VARBITLEN(s);
578601
result= (char*)palloc(len+1);
579602
sp=VARBITS(s);
@@ -620,8 +643,6 @@ varbit_recv(PG_FUNCTION_ARGS)
620643
VarBit*result;
621644
intlen,
622645
bitlen;
623-
intipad;
624-
bits8mask;
625646

626647
bitlen=pq_getmsgint(buf,sizeof(int32));
627648
if (bitlen<0||bitlen>VARBITMAXLEN)
@@ -646,13 +667,8 @@ varbit_recv(PG_FUNCTION_ARGS)
646667

647668
pq_copymsgbytes(buf, (char*)VARBITS(result),VARBITBYTES(result));
648669

649-
/* Make sure last byte is zero-padded if needed */
650-
ipad=VARBITPAD(result);
651-
if (ipad>0)
652-
{
653-
mask=BITMASK <<ipad;
654-
*(VARBITS(result)+VARBITBYTES(result)-1) &=mask;
655-
}
670+
/* Make sure last byte is correctly zero-padded */
671+
VARBIT_PAD(result);
656672

657673
PG_RETURN_VARBIT_P(result);
658674
}
@@ -729,8 +745,6 @@ varbit(PG_FUNCTION_ARGS)
729745
boolisExplicit=PG_GETARG_BOOL(2);
730746
VarBit*result;
731747
intrlen;
732-
intipad;
733-
bits8mask;
734748

735749
/* No work if typmod is invalid or supplied data matches it already */
736750
if (len <=0||len >=VARBITLEN(arg))
@@ -749,13 +763,8 @@ varbit(PG_FUNCTION_ARGS)
749763

750764
memcpy(VARBITS(result),VARBITS(arg),VARBITBYTES(result));
751765

752-
/* Make sure last byte is zero-padded if needed */
753-
ipad=VARBITPAD(result);
754-
if (ipad>0)
755-
{
756-
mask=BITMASK <<ipad;
757-
*(VARBITS(result)+VARBITBYTES(result)-1) &=mask;
758-
}
766+
/* Make sure last byte is correctly zero-padded */
767+
VARBIT_PAD(result);
759768

760769
PG_RETURN_VARBIT_P(result);
761770
}
@@ -1013,6 +1022,8 @@ bit_catenate(VarBit *arg1, VarBit *arg2)
10131022
}
10141023
}
10151024

1025+
/* The pad bits should be already zero at this point */
1026+
10161027
returnresult;
10171028
}
10181029

@@ -1046,14 +1057,12 @@ bitsubstring(VarBit *arg, int32 s, int32 l, bool length_not_specified)
10461057
intbitlen,
10471058
rbitlen,
10481059
len,
1049-
ipad=0,
10501060
ishift,
10511061
i;
10521062
inte,
10531063
s1,
10541064
e1;
1055-
bits8mask,
1056-
*r,
1065+
bits8*r,
10571066
*ps;
10581067

10591068
bitlen=VARBITLEN(arg);
@@ -1118,13 +1127,9 @@ bitsubstring(VarBit *arg, int32 s, int32 l, bool length_not_specified)
11181127
r++;
11191128
}
11201129
}
1121-
/* Do we need to pad at the end? */
1122-
ipad=VARBITPAD(result);
1123-
if (ipad>0)
1124-
{
1125-
mask=BITMASK <<ipad;
1126-
*(VARBITS(result)+len-1) &=mask;
1127-
}
1130+
1131+
/* Make sure last byte is correctly zero-padded */
1132+
VARBIT_PAD(result);
11281133
}
11291134

11301135
returnresult;
@@ -1246,7 +1251,7 @@ bit_and(PG_FUNCTION_ARGS)
12461251
for (i=0;i<VARBITBYTES(arg1);i++)
12471252
*r++=*p1++&*p2++;
12481253

1249-
/* Padding is not needed as & of 0pad is 0 */
1254+
/* Padding is not needed as & of 0pads is 0 */
12501255

12511256
PG_RETURN_VARBIT_P(result);
12521257
}
@@ -1268,7 +1273,6 @@ bit_or(PG_FUNCTION_ARGS)
12681273
bits8*p1,
12691274
*p2,
12701275
*r;
1271-
bits8mask;
12721276

12731277
bitlen1=VARBITLEN(arg1);
12741278
bitlen2=VARBITLEN(arg2);
@@ -1287,13 +1291,7 @@ bit_or(PG_FUNCTION_ARGS)
12871291
for (i=0;i<VARBITBYTES(arg1);i++)
12881292
*r++=*p1++ |*p2++;
12891293

1290-
/* Pad the result */
1291-
mask=BITMASK <<VARBITPAD(result);
1292-
if (mask)
1293-
{
1294-
r--;
1295-
*r &=mask;
1296-
}
1294+
/* Padding is not needed as | of 0 pads is 0 */
12971295

12981296
PG_RETURN_VARBIT_P(result);
12991297
}
@@ -1315,7 +1313,6 @@ bitxor(PG_FUNCTION_ARGS)
13151313
bits8*p1,
13161314
*p2,
13171315
*r;
1318-
bits8mask;
13191316

13201317
bitlen1=VARBITLEN(arg1);
13211318
bitlen2=VARBITLEN(arg2);
@@ -1335,13 +1332,7 @@ bitxor(PG_FUNCTION_ARGS)
13351332
for (i=0;i<VARBITBYTES(arg1);i++)
13361333
*r++=*p1++ ^*p2++;
13371334

1338-
/* Pad the result */
1339-
mask=BITMASK <<VARBITPAD(result);
1340-
if (mask)
1341-
{
1342-
r--;
1343-
*r &=mask;
1344-
}
1335+
/* Padding is not needed as ^ of 0 pads is 0 */
13451336

13461337
PG_RETURN_VARBIT_P(result);
13471338
}
@@ -1357,7 +1348,6 @@ bitnot(PG_FUNCTION_ARGS)
13571348
VarBit*result;
13581349
bits8*p,
13591350
*r;
1360-
bits8mask;
13611351

13621352
result= (VarBit*)palloc(VARSIZE(arg));
13631353
SET_VARSIZE(result,VARSIZE(arg));
@@ -1368,13 +1358,8 @@ bitnot(PG_FUNCTION_ARGS)
13681358
for (;p<VARBITEND(arg);p++)
13691359
*r++= ~*p;
13701360

1371-
/* Pad the result */
1372-
mask=BITMASK <<VARBITPAD(result);
1373-
if (mask)
1374-
{
1375-
r--;
1376-
*r &=mask;
1377-
}
1361+
/* Must zero-pad the result, because extra bits are surely 1's here */
1362+
VARBIT_PAD_LAST(result,r);
13781363

13791364
PG_RETURN_VARBIT_P(result);
13801365
}
@@ -1441,6 +1426,8 @@ bitshiftleft(PG_FUNCTION_ARGS)
14411426
*r=0;
14421427
}
14431428

1429+
/* The pad bits should be already zero at this point */
1430+
14441431
PG_RETURN_VARBIT_P(result);
14451432
}
14461433

@@ -1507,6 +1494,8 @@ bitshiftright(PG_FUNCTION_ARGS)
15071494
if ((++r)<VARBITEND(result))
15081495
*r= (*p << (BITS_PER_BYTE-ishift))&BITMASK;
15091496
}
1497+
/* We may have shifted 1's into the pad bits, so fix that */
1498+
VARBIT_PAD_LAST(result,r);
15101499
}
15111500

15121501
PG_RETURN_VARBIT_P(result);

‎src/include/utils/varbit.h

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -21,6 +21,11 @@
2121

2222
/*
2323
* Modeled on struct varlena from postgres.h, but data type is bits8.
24+
*
25+
* Caution: if bit_len is not a multiple of BITS_PER_BYTE, the low-order
26+
* bits of the last byte of bit_dat[] are unused and MUST be zeroes.
27+
* (This allows bit_cmp() to not bother masking the last byte.)
28+
* Also, there should not be any excess bytes counted in the header length.
2429
*/
2530
typedefstruct
2631
{

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