Bug#343140: libc6: resolver always checks search list in /etc/resolv.conf
tag 343140 + fixed-upstream
close 343140 2.9-1
found 343140 2.9-6
thanks
On Mon, Dec 12, 2005 at 09:13:13PM -0800, Edward Buck wrote:
> Package: libc6
> Version: 2.3.2.ds1-22
> Severity: important
>
> I originally posted a bug report for postfix detailing the problem but I
> can reproduce the bug outside of postfix. Here's the postfix bug
> report in case you're interested:
>
> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=314891
>
> In a nutshell, when using 'search' lines in /etc/resolv.conf, the
> resolver always appends listed search domains to a hostname lookup even
> when the host being searched is fully-qualified (contains one or more dots).
> This results in a LOT of needless DNS traffic. On a busy mail server,
> it makes using the 'search' lines extremely expensive (because DNS traffic
> increases exponentially).
>
> Here's an strace of 'telnet mx1.hotmail.com 25'. Oddly, it seems to do
> the right thing initially but the fully-qualified lookup must always
> fail, resulting in subsequent lookups using the search list.
>
> $ cat /etc/resolv.conf
> nameserver 69.51.81.36
> nameserver 69.51.78.68
> search ul.aspextra.net aspextra.net
>
> $ strace telnet mx1.hotmail.com 25
> ...
> open("/etc/resolv.conf", O_RDONLY) = 3
> fstat64(3, {st_mode=S_IFREG|0644, st_size=274, ...}) = 0
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40018000
> read(3, "# Dynamic resolv.conf(5) file fo"..., 4096) = 274
> read(3, "", 4096) = 0
> close(3) = 0
> munmap(0x40018000, 4096) = 0
> socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 3
> connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("69.51.81.36")}, 28) = 0
> send(3, "\n\177\1\0\0\1\0\0\0\0\0\0\3mx1\7hotmail\3com\0\0\34\0"..., 33, 0) = 33
> gettimeofday({1134449292, 353764}, NULL) = 0
> poll([{fd=3, events=POLLIN, revents=POLLIN}], 1, 5000) = 1
> ioctl(3, FIONREAD, [98]) = 0
> recvfrom(3, "\n\177\201\200\0\1\0\0\0\1\0\0\3mx1\7hotmail\3com\0\0\34"..., 1024, 0, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("69.51.81.36")}, [16]) = 98
> close(3) = 0
> socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 3
> connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("69.51.81.36")}, 28) = 0
> send(3, "\n\200\1\0\0\1\0\0\0\0\0\0\3mx1\7hotmail\3com\2ul\10"..., 49, 0) = 49
> gettimeofday({1134449292, 357407}, NULL) = 0
> poll([{fd=3, events=POLLIN, revents=POLLIN}], 1, 5000) = 1
> ioctl(3, FIONREAD, [49]) = 0
> recvfrom(3, "\n\200\201\205\0\1\0\0\0\0\0\0\3mx1\7hotmail\3com\2ul\10"..., 1024, 0, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("69.51.81.36")}, [16]) = 49
> close(3) = 0
> socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 3
> connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("69.51.78.68")}, 28) = 0
> send(3, "\n\200\1\0\0\1\0\0\0\0\0\0\3mx1\7hotmail\3com\2ul\10"..., 49, 0) = 49
> gettimeofday({1134449292, 361191}, NULL) = 0
> poll([{fd=3, events=POLLIN, revents=POLLIN}], 1, 3000) = 1
> ioctl(3, FIONREAD, [100]) = 0
> recvfrom(3, "\n\200\201\203\0\1\0\0\0\1\0\0\3mx1\7hotmail\3com\2ul\10"..., 1024, 0, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("69.51.78.68")}, [16]) = 100
> close(3) = 0
> socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 3
> connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("69.51.81.36")}, 28) = 0
> send(3, "\n\201\1\0\0\1\0\0\0\0\0\0\3mx1\7hotmail\3com\10asp"..., 46, 0) = 46
> gettimeofday({1134449292, 364427}, NULL) = 0
> poll([{fd=3, events=POLLIN, revents=POLLIN}], 1, 5000) = 1
> ioctl(3, FIONREAD, [97]) = 0
> recvfrom(3, "\n\201\201\203\0\1\0\0\0\1\0\0\3mx1\7hotmail\3com\10as"..., 1024, 0, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("69.51.81.36")}, [16]) = 97
> close(3) = 0
> socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 3
> connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("69.51.81.36")}, 28) = 0
> send(3, "\n\202\1\0\0\1\0\0\0\0\0\0\3mx1\7hotmail\3com\0\0\1\0"..., 33, 0) = 33
> gettimeofday({1134449292, 367710}, NULL) = 0
> poll([{fd=3, events=POLLIN, revents=POLLIN}], 1, 5000) = 1
> ioctl(3, FIONREAD, [195]) = 0
> recvfrom(3, "\n\202\201\200\0\1\0\4\0\5\0\0\3mx1\7hotmail\3com\0\0\1"..., 1024, 0, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("69.51.81.36")}, [16]) = 195
> close(3) = 0
> socket(PF_FILE, SOCK_STREAM, 0) = 3
> connect(3, {sa_family=AF_FILE, path="/var/run/.nscd_socket"}, 110) = -1 ENOENT (No such file or directory)
> close(3) = 0
> gettimeofday({1134449292, 371589}, NULL) = 0
> getpid() = 15269
> open("/etc/resolv.conf", O_RDONLY) = 3
> ...
>
This bug is fixed by unified IPv6 and IPv4 lookup since glibc 2.9-1.
Unfortunately we had to disable this feature in glibc 2.9-6 due to
broken SOHO routers. See bug#516218.
--
Aurelien Jarno GPG: 1024D/F1BCDB73
aurelien@aurel32.net http://www.aurel32.net
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