[PATCH] do not use gethostbyname() for hostname -s

Mon Dec 16 06:48:26 UTC 2013

On Monday 16 December 2013 03:29:01 Denys Vlasenko wrote:
> On Monday 09 December 2013 18:56, Michael Tokarev wrote:
> > There's no reason to call gethostbyname() on the value returned
> > by uname() when asked just for a short name of a host.  This may
> > also be wrong, when uname is set to one value, but in /etc/hosts
> > (or elsewhere) the "canonical" name is different.  This is often
> > the case for localhost entry in /etc/hosts:
> > 
> >   127.0.0.1	localhost	myname
> > 
> > With this content of /etc/hosts, and uname being set to myname,
> > busybox hostname -s will return localhost, while regular
> > hostname utility returns myname.
> 
> Can you send strace of regular hostname's run?
> I would like to see whether it does any name resolution...
> 
> 
Hi,
attached strace for hostname and hostname -s.

Ciao,
Tito
-------------- next part --------------
execve("/bin/hostname", ["hostname", "-s"], [/* 43 vars */]) = 0
brk(0)                                  = 0x872d000
uname({sys="Linux", node="debian", ...}) = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7778000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY)      = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=139871, ...}) = 0
mmap2(NULL, 139871, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7755000
close(3)                                = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/i386-linux-gnu/i686/cmov/libnsl.so.1", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0P1\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0644, st_size=79728, ...}) = 0
mmap2(NULL, 92136, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb773e000
mmap2(0xb7751000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x12) = 0xb7751000
mmap2(0xb7753000, 6120, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb7753000
close(3)                                = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/i386-linux-gnu/i686/cmov/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\240o\1\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=1437864, ...}) = 0
mmap2(NULL, 1452408, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb75db000
mprotect(0xb7737000, 4096, PROT_NONE)   = 0
mmap2(0xb7738000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x15c) = 0xb7738000
mmap2(0xb773b000, 10616, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb773b000
close(3)                                = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb75da000
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb75d9000
set_thread_area({entry_number:-1 -> 6, base_addr:0xb75dab40, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0
mprotect(0xb7738000, 8192, PROT_READ)   = 0
mprotect(0xb7751000, 4096, PROT_READ)   = 0
mprotect(0x804b000, 4096, PROT_READ)    = 0
mprotect(0xb7796000, 4096, PROT_READ)   = 0
munmap(0xb7755000, 139871)              = 0
brk(0)                                  = 0x872d000
brk(0x874e000)                          = 0x874e000
uname({sys="Linux", node="debian", ...}) = 0
fstat64(1, {st_mode=S_IFCHR|0600, st_rdev=makedev(136, 1), ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7777000
write(1, "debian\n", 7)                 = 7
exit_group(0)                           = ?
-------------- next part --------------
execve("/bin/hostname", ["hostname"], [/* 43 vars */]) = 0
brk(0)                                  = 0x8b9b000
uname({sys="Linux", node="debian", ...}) = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb76f4000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY)      = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=139871, ...}) = 0
mmap2(NULL, 139871, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb76d1000
close(3)                                = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/i386-linux-gnu/i686/cmov/libnsl.so.1", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0P1\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0644, st_size=79728, ...}) = 0
mmap2(NULL, 92136, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb76ba000
mmap2(0xb76cd000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x12) = 0xb76cd000
mmap2(0xb76cf000, 6120, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb76cf000
close(3)                                = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/i386-linux-gnu/i686/cmov/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\240o\1\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=1437864, ...}) = 0
mmap2(NULL, 1452408, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7557000
mprotect(0xb76b3000, 4096, PROT_NONE)   = 0
mmap2(0xb76b4000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x15c) = 0xb76b4000
mmap2(0xb76b7000, 10616, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb76b7000
close(3)                                = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7556000
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7555000
set_thread_area({entry_number:-1 -> 6, base_addr:0xb7556b40, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0
mprotect(0xb76b4000, 8192, PROT_READ)   = 0
mprotect(0xb76cd000, 4096, PROT_READ)   = 0
mprotect(0x804b000, 4096, PROT_READ)    = 0
mprotect(0xb7712000, 4096, PROT_READ)   = 0
munmap(0xb76d1000, 139871)              = 0
brk(0)                                  = 0x8b9b000
brk(0x8bbc000)                          = 0x8bbc000
uname({sys="Linux", node="debian", ...}) = 0
fstat64(1, {st_mode=S_IFCHR|0600, st_rdev=makedev(136, 1), ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb76f3000
write(1, "debian\n", 7)                 = 7
exit_group(0)                           = ?