Re: [BUGS] 回复： [BUGS] BUG #13762: server will crash after superuser alter function and set client_encoding

On Tue, Nov 10, 2015 at 9:51 AM, 笑见江湖 <funnyxj@qq.com> wrote:
> Although its is in the category of "don't do that",  but server crashed is
> dangerous. If I alter a function to "set work_mem = '4MB'", it should be no
> problem and reasonable.

ALTERing a system function reserved for encoding is not that much a
good idea, following Tom's point.

> Sorry, the correct statements which make server crash is:
>
> 1. alter function koi8r_to_utf8(integer, integer, cstring, internal,
> integer) set work_mem = '4MB';
> 2. set client_encoding = 'koi8';
> 3. select 1;

This indeed crashes, and that's not limited to this particular
function, try for example iso8859_to_utf8 with ISO_8859_6 as
client_encoding on even a different parameter for the same result.
FWIW, here is a backtrace with assertions enabled:
    frame #2: 0x000000010b3a9949
postgres`ExceptionalCondition(conditionName=0x000000010b4a9b13,
errorType=0x000000010b417495, fileName=0x000000010b4cd1cf,
lineNumber=1127) + 137 at assert.c:54
    frame #3: 0x000000010b383709
postgres`SearchCatCache(cache=0x00007fa36985e5f8, v1=12262, v2=0,
v3=0, v4=0) + 89 at catcache.c:1127
    frame #4: 0x000000010b39dc0c postgres`SearchSysCache(cacheId=42,
key1=12262, key2=0, key3=0, key4=0) + 172 at syscache.c:981
    frame #5: 0x000000010b3b4333
postgres`fmgr_info_cxt_security(functionId=12262,
finfo=0x00007fa369872a88, mcxt=0x00007fa369404610,
ignore_security='\x01') + 227 at fmgr.c:215
    frame #6: 0x000000010b3b92a3
postgres`fmgr_security_definer(fcinfo=0x00007fff54e7c8a8) + 115 at
fmgr.c:905
    frame #7: 0x000000010b3b664c
postgres`FunctionCall5Coll(flinfo=0x00007fa369872e60, collation=0,
arg1=26, arg2=6, arg3=140339826604600, arg4=140339826606696, arg5=9) +
220 at fmgr.c:1404
    frame #8: 0x000000010b3c810e
postgres`perform_default_encoding_conversion(src=0x00007fa369833a38,
len=9, is_client_to_server='\x01') + 382 at mbutils.c:715
    frame #9: 0x000000010b3c7f5b
postgres`pg_any_to_server(s=0x00007fa369833a38, len=9, encoding=26) +
459 at mbutils.c:619
    frame #10: 0x000000010b3c7d85
postgres`pg_client_to_server(s=0x00007fa369833a38, len=9) + 37 at
mbutils.c:558

frame #3: 0x000000010b383709
postgres`SearchCatCache(cache=0x00007fa36985e5f8, v1=12262, v2=0,
v3=0, v4=0) + 89 at catcache.c:1127
   1124        HeapTuple    ntp;
   1125
   1126        /* Make sure we're in an xact, even if this ends up
being a cache hit */
-> 1127        Assert(IsTransactionState());

This is basically trying to do a relcache lookup without being in a
transaction block, so well... That's really in the category of don't
do that. Encoding conversions are not aimed at happening within a
transaction context.
--
Michael