[nsd-users] nsd-zonec SIGSEGV when record is longer than 255 characters

Ilya Bakulin Ilya_Bakulin at genua.de
Mon Aug 27 14:02:18 UTC 2012

We have found incorrect processing of long records by nsd-zonec.
Suppose we have such record in zone file:
longrecord                             TXT     "aaa....aaa"
where "aaa...aaa" is longer than 255 characters. Then by parsing this zone 
file nsd-zonec prints error message and then segfaults:

root at ggd114:# nsd-zonec -c /cage/nsd/etc/nsd-auth_policy.conf
/cage/nsd/var/nsd/zones/second_zone.zone:15: error: text string is longer than 
255 characters, try splitting it into multiple parts
Segmentation fault (core dumped)

gdb output:
$ gdb obj/nsd-zonec nsd-zonec.core                                                                       
GNU gdb 6.3
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There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i386-unknown-openbsd5.1"...
Core was generated by `nsd-zonec'.
Program terminated with signal 11, Segmentation fault.
Reading symbols from /usr/lib/libcrypto.so.20.1...done.
Loaded symbols for /usr/lib/libcrypto.so.20.1
Reading symbols from /usr/lib/libc.so.62.0...done.
Loaded symbols for /usr/lib/libc.so.62.0
Reading symbols from /usr/libexec/ld.so...done.
Loaded symbols for /usr/libexec/ld.so
#0  0x1c016d3d in zadd_rdata_txt_wireformat (data=0x0, first=1) 
at /data/home/ibaku/nsd/zonec.c:970
970             if ((size_t)rd->data[0] + (size_t)data[0] > 65535) {
(gdb) bt
#0  0x1c016d3d in zadd_rdata_txt_wireformat (data=0x0, first=1) 
at /data/home/ibaku/nsd/zonec.c:970
#1  0x1c01b3ad in yyparse () at zparser.y:337
#2  0x1c016392 in zone_read (name=0x88904350 "zone2", 
    zonefile=0x88904384 "/cage/nsd/var/nsd/zones/second_zone.zone", 
    at /data/home/ibaku/nsd/zonec.c:1418
#3  0x1c016980 in main (argc=0, argv=0x0) at /data/home/ibaku/nsd/zonec.c:1605

The real problem is that the function zparser_conv_text() returns NULL pointer 
when it tries to process this long string. This is then used without further 
checks at zonec.c:970, that causes null pointer dereference.

I'm not sure how to better fix this, but probably it's safe to return _some_ 
valid pointer to let nsd-zonec scan file to the end and produce error output 
without coredumping. I have tested this and it works.


Best regards,
Ilya Bakulin

Gesellschaft fuer Netzwerk- und Unix-Administration mbH
Domagkstrasse 7, 85551 Kirchheim bei Muenchen
tel +49 89 991950-0, fax -999, www.genua.de
Geschaeftsfuehrer: Dr. Magnus Harlander, Dr. Michaela Harlander,
Bernhard Schneck. Amtsgericht Muenchen HRB 98238
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