Thread: CREATE TEXT SEARCH DICTIONARY segfaulting on 9.6+
Hi,
over in pgsql-bugs [1] we got a report about CREATE TEXT SEARCH
DICTIONARY causing segfaults on 12.0. Simply running
CREATE TEXT SEARCH DICTIONARY hunspell_num (Template=ispell,
DictFile=hunspell_sample_num, AffFile=hunspell_sample_long);
does trigger a crash, 100% of the time. The crash was reported on 12.0,
but it's in fact present since 9.6.
On 9.5 the example does not work, because that version does not (a)
include the hunspell dictionaries used in the example, and (b) it does
not support long flags. So even after copying the dictionaries and
tweaking them a bit it still passes without a crash.
Looking at the commit history of spell.c, there seems to be a bunch of
commits in 2016 (e.g. f4ceed6ceba3) touching exactly this part of the
code (hunspell), and it also correlates quite nicely with the affected
branches (9.6+). So my best guess is it's a bug in those changes.
A complete backtrace looks like this:
Program received signal SIGSEGV, Segmentation fault.
0x00000000008fca10 in getCompoundAffixFlagValue (Conf=0x20dd3b8, s=0x7f7f7f7f7f7f7f7f <error: Cannot access memory at
address0x7f7f7f7f7f7f7f7f>) at spell.c:1126
1126 while (*flagcur)
(gdb) bt
#0 0x00000000008fca10 in getCompoundAffixFlagValue (Conf=0x20dd3b8, s=0x7f7f7f7f7f7f7f7f <error: Cannot access memory
ataddress 0x7f7f7f7f7f7f7f7f>) at spell.c:1126
#1 0x00000000008fdd1c in makeCompoundFlags (Conf=0x20dd3b8, affix=303) at spell.c:1608
#2 0x00000000008fe04e in mkSPNode (Conf=0x20dd3b8, low=0, high=1, level=3) at spell.c:1680
#3 0x00000000008fe113 in mkSPNode (Conf=0x20dd3b8, low=0, high=1, level=2) at spell.c:1692
#4 0x00000000008fde89 in mkSPNode (Conf=0x20dd3b8, low=0, high=4, level=1) at spell.c:1652
#5 0x00000000008fde89 in mkSPNode (Conf=0x20dd3b8, low=0, high=9, level=0) at spell.c:1652
#6 0x00000000008fe50b in NISortDictionary (Conf=0x20dd3b8) at spell.c:1785
#7 0x00000000008f9e14 in dispell_init (fcinfo=0x7ffdda6abc90) at dict_ispell.c:89
#8 0x0000000000a6210a in FunctionCall1Coll (flinfo=0x7ffdda6abcf0, collation=0, arg1=34478896) at fmgr.c:1140
#9 0x0000000000a62c72 in OidFunctionCall1Coll (functionId=3731, collation=0, arg1=34478896) at fmgr.c:1418
#10 0x00000000006c2dcb in verify_dictoptions (tmplId=3733, dictoptions=0x20e1b30) at tsearchcmds.c:402
#11 0x00000000006c2f4c in DefineTSDictionary (names=0x20ba278, parameters=0x20ba458) at tsearchcmds.c:463
#12 0x00000000008eb274 in ProcessUtilitySlow (pstate=0x20db518, pstmt=0x20bab88, queryString=0x20b97a8 "CREATE TEXT
SEARCHDICTIONARY hunspell_num (Template=ispell,\nDictFile=hunspell_sample_num, AffFile=hunspell_sample_long);",
context=PROCESS_UTILITY_TOPLEVEL,params=0x0, queryEnv=0x0, dest=0x20bac80,
completionTag=0x7ffdda6ac540 "") at utility.c:1272
#13 0x00000000008ea7e5 in standard_ProcessUtility (pstmt=0x20bab88, queryString=0x20b97a8 "CREATE TEXT SEARCH
DICTIONARYhunspell_num (Template=ispell,\nDictFile=hunspell_sample_num, AffFile=hunspell_sample_long);",
context=PROCESS_UTILITY_TOPLEVEL,params=0x0, queryEnv=0x0, dest=0x20bac80,
completionTag=0x7ffdda6ac540 "") at utility.c:927
#14 0x00000000008e991a in ProcessUtility (pstmt=0x20bab88, queryString=0x20b97a8 "CREATE TEXT SEARCH DICTIONARY
hunspell_num(Template=ispell,\nDictFile=hunspell_sample_num, AffFile=hunspell_sample_long);",
context=PROCESS_UTILITY_TOPLEVEL,params=0x0, queryEnv=0x0, dest=0x20bac80, completionTag=0x7ffdda6ac540 "")
at utility.c:360
#15 0x00000000008e88e1 in PortalRunUtility (portal=0x2121368, pstmt=0x20bab88, isTopLevel=true, setHoldSnapshot=false,
dest=0x20bac80,completionTag=0x7ffdda6ac540 "") at pquery.c:1175
#16 0x00000000008e8afe in PortalRunMulti (portal=0x2121368, isTopLevel=true, setHoldSnapshot=false, dest=0x20bac80,
altdest=0x20bac80,completionTag=0x7ffdda6ac540 "") at pquery.c:1321
#17 0x00000000008e8032 in PortalRun (portal=0x2121368, count=9223372036854775807, isTopLevel=true, run_once=true,
dest=0x20bac80,altdest=0x20bac80, completionTag=0x7ffdda6ac540 "") at pquery.c:796
#18 0x00000000008e1f51 in exec_simple_query (query_string=0x20b97a8 "CREATE TEXT SEARCH DICTIONARY hunspell_num
(Template=ispell,\nDictFile=hunspell_sample_num,AffFile=hunspell_sample_long);") at postgres.c:1215
#19 0x00000000008e6243 in PostgresMain (argc=1, argv=0x20e54f8, dbname=0x20e5340 "test", username=0x20b53e8 "user") at
postgres.c:4236
#20 0x000000000083c5e2 in BackendRun (port=0x20dd980) at postmaster.c:4437
#21 0x000000000083bdb3 in BackendStartup (port=0x20dd980) at postmaster.c:4128
#22 0x00000000008381d7 in ServerLoop () at postmaster.c:1704
#23 0x0000000000837a83 in PostmasterMain (argc=3, argv=0x20b3350) at postmaster.c:1377
#24 0x0000000000759507 in main (argc=3, argv=0x20b3350) at main.c:228
(gdb) up
#1 0x00000000008fdd1c in makeCompoundFlags (Conf=0x20dd3b8, affix=303) at spell.c:1608
1608 return (getCompoundAffixFlagValue(Conf, str) & FF_COMPOUNDFLAGMASK);
(gdb) p *Conf
$1 = {maffixes = 16, naffixes = 10, Affix = 0x2181fd0, Suffix = 0x0, Prefix = 0x0, Dictionary = 0x0, AffixData =
0x20e1fa8,lenAffixData = 12, nAffixData = 12, useFlagAliases = true, CompoundAffix = 0x0, usecompound = true, flagMode
=FM_LONG, CompoundAffixFlags = 0x217d328, nCompoundAffixFlag = 6,
mCompoundAffixFlag = 10, buildCxt = 0x217cf20, Spell = 0x7bd99b4f6050, nspell = 9, mspell = 20480, firstfree =
0x217f1b8"", avail = 7608}
(gdb) p affix
$2 = 303
So the affix value is rather strange, because it's clearly outside the
set of flags in Conf (it only has 12 items, so 303 is waaaay too high).
I don't have time to investigate this further and I'm getting lost in
spell.c, so I'm adding Teodor who committed f4ceed6ceba3 in 2016. One
interesting fact is that this is likely due to some discrepancy between
the dictfile and afffile - the segfaulting command appers to mix
hunspell_sample_num and hunspell_sample_long:
CREATE TEXT SEARCH DICTIONARY hunspell_num (Template=ispell,
DictFile=hunspell_sample_num, AffFile=hunspell_sample_long);
But when using the "same" group for both dictfile and afffile, it seems
to work just fine.
[1] https://www.postgresql.org/message-id/flat/16050-024ae722464ab604%40postgresql.org
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
I spent a bit of time investigating this, and it seems the new code is
somewhat too trusting when it comes to data from the affix/dict files.
In this particular case, it boils down to this code in NISortDictionary:
if (Conf->useFlagAliases)
{
for (i = 0; i < Conf->nspell; i++)
{
char *end;
if (*Conf->Spell[i]->p.flag != '\0')
{
curaffix = strtol(Conf->Spell[i]->p.flag, &end, 10);
if (Conf->Spell[i]->p.flag == end || errno == ERANGE)
ereport(ERROR,
(errcode(ERRCODE_CONFIG_FILE_ERROR),
errmsg("invalid affix alias \"%s\"",
Conf->Spell[i]->p.flag)));
}
...
Conf->Spell[i]->p.d.affix = curaffix;
...
}
...
}
So it simply grabs whatever it finds in the dict file, parses it and
then (later) we use it as index to access the AffixData array, even if
the value is way out of bounds.
For example in the example, hunspell_sample_long.affix contains about
10 affixes, but then we parse the hunspell_sample_num.dict file, and we
stumble upon
book/302,301,202,303
and we parse the flags as integers, and interpret them as indexes in the
AffixData array. Clearly, 303 is waaaay out of bounds, triggering the
segfault crash.
So I think we need some sort of cross-check here. We certainly need to
make NISortDictionary() check the affix value is within AffixData
bounds, and error out when the index is non-sensical (maybe negative
and/or exceeding nAffixData). Maybe there's a simple way to check if the
affix/dict files match. The failing affix has
FLAG num
while with
FLAG long
it works just fine. But I'm not sure that's actually possible, because I
don't see anything in hunspell_sample_num.dict that would allow us to
decide that it expects "FLAG num" and not "FLAG long". Furthermore, we
certainly can't rely on this - we still need to check the range.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Hello Tomas, On 2019/10/13 10:26, Tomas Vondra wrote: > over in pgsql-bugs [1] we got a report about CREATE TEXT SEARCH > DICTIONARY causing segfaults on 12.0. Simply running > > CREATE TEXT SEARCH DICTIONARY hunspell_num (Template=ispell, > DictFile=hunspell_sample_num, AffFile=hunspell_sample_long); > > does trigger a crash, 100% of the time. The crash was reported on 12.0, > but it's in fact present since 9.6. > > On 9.5 the example does not work, because that version does not (a) > include the hunspell dictionaries used in the example, and (b) it does > not support long flags. So even after copying the dictionaries and > tweaking them a bit it still passes without a crash. This crash is not because of long flags, but because of aliases (more thoughts below). > Looking at the commit history of spell.c, there seems to be a bunch of > commits in 2016 (e.g. f4ceed6ceba3) touching exactly this part of the > code (hunspell), and it also correlates quite nicely with the affected > branches (9.6+). So my best guess is it's a bug in those changes. Yeah, there was a lot changes. > So it simply grabs whatever it finds in the dict file, parses it and > then (later) we use it as index to access the AffixData array, even if > the value is way out of bounds. Yes, we enter this code if an affix file defines aliases (AF parameter). AffixData array is used to store those aliases. More about hunspell format you can find here: https://linux.die.net/man/4/hunspell In the example we have the following aliases: AF 11 AF cZ #1 AF cL #2 ... AF sB #11 And in the dictionary file we should use their indexes (from 1 to 11). These aliases defines set of flags and in the dict file we can use only single index: book/3 book/11 but not: book/3,4 book/2,11 I added checking of this last case in the attached patch. PostgreSQL will raise an error if it sees non-numeric and non-whitespace character after the index. Aliases can be used with all flag types: 'default' (i.e. FM_CHAR), 'long', and if I'm not mistaken 'num'. > So I think we need some sort of cross-check here. We certainly need to > make NISortDictionary() check the affix value is within AffixData > bounds, and error out when the index is non-sensical (maybe negative > and/or exceeding nAffixData). I agree, I attached the patch which do this. I also added couple asserts, tests and fixed condition in getAffixFlagSet(): - if (curaffix > 0 && curaffix <= Conf->nAffixData) + if (curaffix > 0 && curaffix < Conf->nAffixData) I think it could be a bug, because curaffix can't be equal to Conf->nAffixData. > Maybe there's a simple way to check if the affix/dict files match. I'm not sure how to properly fix this either. The only thing we could check is commas in affix flags in a dict file: book/302,301,202,303 FM_CHAR and FM_LONG dictionaries can't have commas. They should have the following affix flags: book/sGsJpUsS # 4 affixes for FM_LONG book/GJUS # 4 affixes for FM_CHAR But I guess they could have numbers in flags (as help says "Set flag type. Default type is the extended ASCII (8-bit) character.") and other non alphanumeric characters (as some language dictionaries have): book/s1s2s3s4 # 4 affixes for FM_LONG -- Artur
Attachment
Arthur Zakirov <zaartur@gmail.com> writes:
> On 2019/10/13 10:26, Tomas Vondra wrote:
>> So I think we need some sort of cross-check here. We certainly need to
>> make NISortDictionary() check the affix value is within AffixData
>> bounds, and error out when the index is non-sensical (maybe negative
>> and/or exceeding nAffixData).
> I agree, I attached the patch which do this. I also added couple
> asserts, tests and fixed condition in getAffixFlagSet():
> - if (curaffix > 0 && curaffix <= Conf->nAffixData)
> + if (curaffix > 0 && curaffix < Conf->nAffixData)
Looks reasonable to me, and we need to get something done before
the upcoming releases, so I pushed this. Perhaps there's more
that could be done later.
regards, tom lane
On Sun, Nov 3, 2019 at 5:48 AM Tom Lane <tgl@sss.pgh.pa.us> wrote: > > Arthur Zakirov <zaartur@gmail.com> writes: > > On 2019/10/13 10:26, Tomas Vondra wrote: > >> So I think we need some sort of cross-check here. We certainly need to > >> make NISortDictionary() check the affix value is within AffixData > >> bounds, and error out when the index is non-sensical (maybe negative > >> and/or exceeding nAffixData). > > > I agree, I attached the patch which do this. I also added couple > > asserts, tests and fixed condition in getAffixFlagSet(): > > > - if (curaffix > 0 && curaffix <= Conf->nAffixData) > > + if (curaffix > 0 && curaffix < Conf->nAffixData) > > Looks reasonable to me, and we need to get something done before > the upcoming releases, so I pushed this. Perhaps there's more > that could be done later. Great, thank you! -- Artur