Network not functioning on an ARM Linux rootfs with fakeroot/fakechroot

Question

I have created a rootfs using buildroot, but using a crosstool-ng tool chain with glibc. This showed me the minimal set of files necessary. I then replaced all the libraries with ones pulled straight from the squeeze .deb packages for armel. I then added fakeroot and fakechroot to the mix (also from .deb packages). I also modified the resolv.conf, hosts, and nsswitch.conf files to my liking. After uploading this to my device, a lot is working. cd / takes me to the correct place. whoami returns root. But, anything DNS related is not working. For example ping google.com returns bad address. I have copied the libnss_* and libresolv libraries over and everything else I think is necessary. Entering the same setup, but using qemu and chroot on my host machine works, but I am trying to figure out what it is not working on my target device.

When I run strace ping google.com I get the following:

open("/data/local/target/bin/ping", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\2\0(\0\1\0\0\0\0\314\0\0004\0\0\0"..., 4094) = 4094
close(3)                                = 0
execve("/data/local/target/bin/ping", ["ping", "google.com"], [/* 20 vars */]) = 0
brk(0)                                  = 0xb5000
uname({sys="Linux", node="localhost", ...}) = 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) = 0x4001d000
open("/data/local/target/usr/lib/fakechroot/libfakechroot.so", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\364\32\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0666, st_size=45540, ...}) = 0
mmap2(NULL, 77628, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x40026000
mprotect(0x40031000, 28672, PROT_NONE)  = 0
mmap2(0x40038000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0xa) = 0x40038000
close(3)                                = 0
open("/data/local/target/usr/lib/libfakeroot/libfakeroot-sysv.so", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\340'\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0666, st_size=29092, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x4001f000
mmap2(NULL, 60672, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x40039000
mprotect(0x40040000, 28672, PROT_NONE)  = 0
mmap2(0x40047000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x6) = 0x40047000
close(3)                                = 0
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("tls/v7l/neon/vfp/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/lib/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\374V\1\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=1209660, ...}) = 0
mmap2(NULL, 1246468, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x40048000
mprotect(0x4016b000, 32768, PROT_NONE)  = 0
mmap2(0x40173000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x123) = 0x40173000
mmap2(0x40176000, 9476, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x40176000
close(3)                                = 0
open("tls/v7l/neon/vfp/libdl.so.2", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/lib/libdl.so.2", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0$\t\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=9808, ...}) = 0
mmap2(NULL, 41136, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x40179000
mprotect(0x4017b000, 28672, PROT_NONE)  = 0
mmap2(0x40182000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1) = 0x40182000
close(3)                                = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40020000
set_tls(0x40020170, 0x40020847, 0x40020848, 0x40020170, 0x40025000) = 0
mprotect(0x40182000, 4096, PROT_READ)   = 0
mprotect(0x40173000, 8192, PROT_READ)   = 0
mprotect(0xb1000, 4096, PROT_READ)      = 0
mprotect(0x40024000, 4096, PROT_READ)   = 0
brk(0)                                  = 0xb5000
brk(0xd6000)                            = 0xd6000
socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3)                                = 0
socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3)                                = 0
open("/etc/nsswitch.conf", O_RDONLY)    = -1 ENOENT (No such file or directory)
open("tls/v7l/neon/vfp/libnss_compat.so.2", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/lib/libnss_compat.so.2", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0|\r\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=26480, ...}) = 0
mmap2(NULL, 57952, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x40184000
mprotect(0x4018a000, 28672, PROT_NONE)  = 0
mmap2(0x40191000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x5) = 0x40191000
close(3)                                = 0
open("tls/v7l/neon/vfp/libnsl.so.1", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/lib/libnsl.so.1", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0x/\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=75732, ...}) = 0
mmap2(NULL, 116488, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x40193000
mprotect(0x401a5000, 28672, PROT_NONE)  = 0
mmap2(0x401ac000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x11) = 0x401ac000
mmap2(0x401ae000, 5896, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x401ae000
close(3)                                = 0
mprotect(0x401ac000, 4096, PROT_READ)   = 0
mprotect(0x40191000, 4096, PROT_READ)   = 0
open("/etc/nsswitch.conf", O_RDONLY)    = -1 ENOENT (No such file or directory)
open("tls/v7l/neon/vfp/libnss_nis.so.2", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/usr/lib/libnss_nis.so.2", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/data/local/target/lib/libnss_nis.so.2", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0X\30\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=38608, ...}) = 0
mmap2(NULL, 70236, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x401b0000
mprotect(0x401b9000, 28672, PROT_NONE)  = 0
mmap2(0x401c0000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x8) = 0x401c0000
close(3)                                = 0
open("tls/v7l/neon/vfp/libnss_files.so.2", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/lib/libnss_files.so.2", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\330\31\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=42688, ...}) = 0
mmap2(NULL, 74492, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x401c2000
mprotect(0x401cc000, 28672, PROT_NONE)  = 0
mmap2(0x401d3000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x9) = 0x401d3000
close(3)                                = 0
mprotect(0x401d3000, 4096, PROT_READ)   = 0
mprotect(0x401c0000, 4096, PROT_READ)   = 0
open("/data/local/target/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
fcntl64(3, F_GETFD)                     = 0x1 (flags FD_CLOEXEC)
_llseek(3, 0, [0], SEEK_CUR)            = 0
fstat64(3, {st_mode=S_IFREG|0666, st_size=596, ...}) = 0
mmap2(NULL, 596, PROT_READ, MAP_SHARED, 3, 0) = 0x40021000
_llseek(3, 596, [596], SEEK_SET)        = 0
munmap(0x40021000, 596)                 = 0
close(3)                                = 0
getpid()                                = 9034
socket(PF_NETLINK, SOCK_RAW, 0)         = 3
bind(3, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 0
getsockname(3, {sa_family=AF_NETLINK, pid=9034, groups=00000000}, [12]) = 0
gettimeofday({1366748508, 414909}, NULL) = 0
sendto(3, "\24\0\0\0\26\0\1\3\\\355vQ\0\0\0\0\0\0\0\0", 20, 0, {sa_family=AF_NETLINK,     pid=0, groups=00000000}, 12) = 20
recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"0\0\0\0\24\0\2\0\\\355vQJ#\0\0\2\10\200\376\1\0\0\0\10\0\1\0\177\0\0\1"..., 4096}], msg_controllen=0, msg_flags=0}, 0) = 108
recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"@\0\0\0\24\0\2\0\\\355vQJ#\0\0\n\200\200\376\1\0\0\0\24\0\1\0\0\0\0\0"..., 4096}], msg_controllen=0, msg_flags=0}, 0) = 128
recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"\24\0\0\0\3\0\2\0\\\355vQJ#\0\0\0\0\0\0\1\0\0\0\24\0\1\0\0\0\0\0"..., 4096}], msg_controllen=0, msg_flags=0}, 0) = 20
close(3)                                = 0
open("/etc/resolv.conf", O_RDONLY)      = -1 ENOENT (No such file or directory)
uname({sys="Linux", node="localhost", ...}) = 0
socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3)                                = 0
socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3)                                = 0
open("/etc/nsswitch.conf", O_RDONLY)    = -1 ENOENT (No such file or directory)
open("tls/v7l/neon/vfp/libnss_dns.so.2", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/lib/libnss_dns.so.2", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0000\v\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=18040, ...}) = 0
mmap2(NULL, 49316, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x401d5000
mprotect(0x401d9000, 28672, PROT_NONE)  = 0
mmap2(0x401e0000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x3) = 0x401e0000
close(3)                                = 0
open("tls/v7l/neon/vfp/libresolv.so.2", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/lib/libresolv.so.2", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0H$\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=71524, ...}) = 0
mmap2(NULL, 79772, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x401e2000
mmap2(0x401f2000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x10) = 0x401f2000
mmap2(0x401f4000, 6044, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x401f4000
close(3)                                = 0
mprotect(0x401f2000, 4096, PROT_READ)   = 0
mprotect(0x401e0000, 4096, PROT_READ)   = 0
open("/etc/host.conf", O_RDONLY)        = -1 ENOENT (No such file or directory)
stat64("/etc/resolv.conf", 0xbed0eee8)  = -1 ENOENT (No such file or directory)
gettimeofday({1366748508, 437074}, NULL) = 0
socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 3
connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
gettimeofday({1366748508, 438028}, NULL) = 0
poll([{fd=3, events=POLLOUT}], 1, 0)    = 1 ([{fd=3, revents=POLLOUT}])
send(3, "\234\32\1\0\0\1\0\0\0\0\0\0\6google\3com\0\0\1\0\1", 28, MSG_NOSIGNAL) = 28
poll([{fd=3, events=POLLIN}], 1, 5000)  = 1 ([{fd=3, revents=POLLERR}])
close(3)                                = 0
socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 3
connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
gettimeofday({1366748508, 440124}, NULL) = 0
poll([{fd=3, events=POLLOUT}], 1, 0)    = 1 ([{fd=3, revents=POLLOUT}])
send(3, "\234\32\1\0\0\1\0\0\0\0\0\0\6google\3com\0\0\1\0\1", 28, MSG_NOSIGNAL) = 28
poll([{fd=3, events=POLLIN}], 1, 5000)  = 1 ([{fd=3, revents=POLLERR}])
close(3)                                = 0
gettimeofday({1366748508, 441638}, NULL) = 0
socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 3
connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
gettimeofday({1366748508, 442345}, NULL) = 0
poll([{fd=3, events=POLLOUT}], 1, 0)    = 1 ([{fd=3, revents=POLLOUT}])
send(3, "\302\373\1\0\0\1\0\0\0\0\0\0\6google\3com\0\0\1\0\1", 28, MSG_NOSIGNAL) = 28
poll([{fd=3, events=POLLIN}], 1, 5000)  = 1 ([{fd=3, revents=POLLERR}])
close(3)                                = 0
socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 3
connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
gettimeofday({1366748508, 444280}, NULL) = 0
poll([{fd=3, events=POLLOUT}], 1, 0)    = 1 ([{fd=3, revents=POLLOUT}])
send(3, "\302\373\1\0\0\1\0\0\0\0\0\0\6google\3com\0\0\1\0\1", 28, MSG_NOSIGNAL) = 28
poll([{fd=3, events=POLLIN}], 1, 5000)  = 1 ([{fd=3, revents=POLLERR}])
close(3)                                = 0
open("/data/local/target/etc/hosts", O_RDONLY|O_CLOEXEC) = 3
fcntl64(3, F_GETFD)                     = 0x1 (flags FD_CLOEXEC)
fstat64(3, {st_mode=S_IFREG|0666, st_size=40, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40021000
read(3, "127.0.0.1\tlocalhost\n127.0.1.1\tbu"..., 4096) = 40
read(3, "", 4096)                       = 0
close(3)                                = 0
munmap(0x40021000, 4096)                = 0
write(2, "ping: bad address 'google.com'\n", 31) = 31
exit_group(1)                           = ?

A lot went right. It knew to add /data/local/target to the path when searching for executables and libraries. You can see it finds the various libnss_* libraries and it figured out that the host file wasn't simply at /etc/hosts, but why do you think it didn't look in the correct location for nsswitch.conf and resolv.conf? This seems like a fakechroot issue or an issue with how I am using it.

Try `ping 8.8.8.8`; does that work? It did try `/etc/resolv.conf`. Also, `/etc/host.conf` says whether you can use a resolver. You need that one. Are you saying these files should be in */data/local/...* or are you expecting to search */etc/*? Also, you might appreciate *eglibc* if you build your compiler again. — artless noise, Apr 23 '13 at 22:42
Good question and something I should have included as I already tried that. ping 8.8.8.8 works fine, or other ip addresses work fine. I think it should have tried looking under /data/local/target/etc instead of /etc. Which for some reason it did for trying to find the /data/local/target/hosts and some other things, but not certain key files related to this. — corbin, Apr 23 '13 at 22:49
Yes, uClibc and eglibc handle this differently, but I really want debian packages to install nicely and even eventually run debootstrap which will also create something glibc based and would encounter the same issue (I have tried and most worked, but not DNS). — corbin, Apr 23 '13 at 23:32
Sorry, misunderstanding about eglibc. Yes, actually, I am already using it (as mentioned, pulled straight from debian packages). I was thinking of uClibc and musl C library which are not dependent on the libnss* files. I thought that is what you were getting at. — corbin, Apr 23 '13 at 23:58
Looks like the use of fopen in other libraries/executables can be intercepted by the use of LD_PRELOAD pointing at libfakechroot, but not fopen called from within eglibc itself. I think I will have to manually edit the eglibc source and build it. Looks like they did a good job making this easy. — corbin, Apr 24 '13 at 17:29

score 0 · Accepted Answer · answered May 14 '13 at 16:53

Looks like the use of fopen in other libraries/executables can be intercepted by the use of LD_PRELOAD pointing at libfakechroot, but not fopen called from within eglibc itself. You will have to manually edit the eglibc source and build it. Looks like they did a good job making this easy.

This has been tested and works.

Network not functioning on an ARM Linux rootfs with fakeroot/fakechroot

1 Answers1