[clue-tech] Parallel port access as non root user?
Jim Ockers
ockers at ockers.net
Thu Sep 21 11:48:24 MDT 2006
Hi Ed,
Can you please recompile your program so it opens the correct device?
You wrote:
> > open("/dev/port", O_RDWR) = -1 EACCES (Permission denied)
As you can see your process is trying to open /dev/port with major 1
minor 4 and permissions crw-------. The open is failing with EACCES.
It seems you believe that your process is trying to open one of the
parallel port devices with major 6. These are not the same device
class. Major 1 is for memory devices according to /proc/devices.
There is a device handler registered in the kernel for devices with
major 6 ("lp") according to /proc/devices, so opening one of the lp
devices would probably work.
Incidentally your /dev/parport devices are major 99 and are probably
handled by the parport_pc device but for some reason it doesn't show
up in /proc/devices. (It doesn't on my PC either.)
Anyway I think the answer to your problem is that your program is
opening /dev/port which is not the device you think it is opening.
Hope this helps,
Jim
Ed wrote:
>
> Here ya go Jim. The lp device is loaded according to the /proc table.
> This is a RH ES4 system. I threw in a call to lsmod at the bottom.
> Sorry about the html before.
>
> Thanks a ton.
>
> Ed
>
> [root at denali ed]# ls -al /dev/port
> crw------- 1 root kmem 1, 4 Sep 20 09:26 /dev/port
> [root at denali ed]# ls -al /dev/lp*
> crw-rw-rw- 1 root lp 6, 0 Sep 20 09:26 /dev/lp0
> crw-rw-rw- 1 root lp 6, 1 Sep 20 09:26 /dev/lp1
> crw-rw-rw- 1 root lp 6, 2 Sep 20 09:26 /dev/lp2
> crw-rw-rw- 1 root lp 6, 3 Sep 20 09:26 /dev/lp3
> [root at denali ed]# ls -al /dev/parport*
> crw-rw-rw- 1 root lp 99, 0 Sep 20 09:26 /dev/parport0
> crw-rw-rw- 1 root lp 99, 1 Sep 20 09:26 /dev/parport1
> crw-rw-rw- 1 root lp 99, 2 Sep 20 09:26 /dev/parport2
> crw-rw-rw- 1 root lp 99, 3 Sep 20 09:26 /dev/parport3
> [root at denali ed]# cat /proc/devices
> Character devices:
> 1 mem
> 4 /dev/vc/0
> 4 tty
> 4 ttyS
> 5 /dev/tty
> 5 /dev/console
> 5 /dev/ptmx
> 6 lp
> 7 vcs
> 10 misc
> 13 input
> 14 sound
> 29 fb
> 36 netlink
> 89 i2c
> 116 alsa
> 128 ptm
> 136 pts
> 162 raw
> 180 usb
> 226 drm
>
> Block devices:
> 1 ramdisk
> 3 ide0
> 8 sd
> 9 md
> 65 sd
> 66 sd
> 67 sd
> 68 sd
> 69 sd
> 70 sd
> 71 sd
> 128 sd
> 129 sd
> 130 sd
> 131 sd
> 132 sd
> 133 sd
> 134 sd
> 135 sd
> 253 device-mapper
> 254 mdp
>
> [root at denali ed]# /sbin/lsmod
> Module Size Used by
> i915 81541 2
> parport_pc 27905 1
> lp 15405 0
> parport 37641 2 parport_pc,lp
> autofs4 22597 0
> i2c_dev 14273 0
> i2c_core 25921 1 i2c_dev
> sunrpc 142757 1
> button 10449 0
> battery 12869 0
> ac 8773 0
> md5 8001 1
> ipv6 240225 64
> joydev 14209 0
> uhci_hcd 32729 0
> ehci_hcd 31813 0
> hw_random 9557 0
> snd_intel8x0 34921 2
> snd_ac97_codec 65169 1 snd_intel8x0
> snd_pcm_oss 52345 0
> snd_mixer_oss 21825 2 snd_pcm_oss
> snd_pcm 91973 2 snd_intel8x0,snd_pcm_oss
> snd_timer 27973 1 snd_pcm
> snd_page_alloc 13641 2 snd_intel8x0,snd_pcm
> snd_mpu401_uart 11329 1 snd_intel8x0
> snd_rawmidi 27749 1 snd_mpu401_uart
> snd_seq_device 11849 1 snd_rawmidi
> snd 56997 11
> snd_intel8x0,snd_ac97_codec,snd_pcm_oss,snd_mixer_oss,snd_pcm,snd_timer,snd_mpu401_uart,snd_rawmidi,snd_seq_device
> soundcore 12961 2 snd
> tg3 95173 0
> dm_snapshot 20837 0
> dm_zero 6337 0
> dm_mirror 28449 0
> ext3 118729 2
> jbd 59481 1 ext3
> dm_mod 59973 6 dm_snapshot,dm_zero,dm_mirror
> ata_piix 13381 2
> libata 57885 1 ata_piix
> sd_mod 20545 3
> scsi_mod 116941 2 libata,sd_mod
>
> Ed
>
>
>
>
> On 9/21/06, Jim Ockers <ockers at ockers.net> wrote:
> > Ed,
> >
> > I'm top-posting on purpose. In the strace output below I saw this
> > line:
> >
> > open("/dev/port", O_RDWR) = -1 EACCES (Permission denied)
> >
> > Could you please issue the following commands for me:
> >
> > ls -al /dev/port
> > ls -al /dev/lp*
> > ls -al /dev/parport*
> > cat /proc/devices
> >
> > I want to see the major & minor device numbers for each of those. It
> > could be that your error message is due to opening a nonexistent
> > device or device for which the device driver is not loaded, or
> > something.
> >
> > By the way Ed can you just send text e-mails please? The HTML isn't
> > necessary.
> >
> > Thanks,
> > Jim
> >
> > Ed Young wrote:
> > >
> > > ------=_Part_13109_30312243.1158856981302
> > > Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> > > Content-Transfer-Encoding: 7bit
> > > Content-Disposition: inline
> > >
> > > Jim,
> > >
> > > I've set /dev/lp0-3 and /dev/parport0-3 up as 0x666 and added myself to the
> > > lp group in /etc/group
> > >
> > > Check it out:
> > >
> > > [ed at denali k74-1.0]$ strace ./k74 all set
> > > execve("./k74", ["./k74", "all", "set"], [/* 30 vars */]) = 0
> > > uname({sys="Linux", node="denali.comcast.com", ...}) = 0
> > > brk(0) = 0x9bfd000
> > > 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=98174, ...}) = 0
> > > old_mmap(NULL, 98174, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7f37000
> > > close(3) = 0
> > > open("/lib/tls/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\20_\251"..., 512) =
> > > 512
> > > fstat64(3, {st_mode=S_IFREG|0755, st_size=1454546, ...}) = 0
> > > old_mmap(0xa81000, 1219772, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE,
> > > 3, 0) = 0xa81000
> > > old_mmap(0xba5000, 16384, PROT_READ|PROT_WRITE,
> > > MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x124000) = 0xba5000
> > > old_mmap(0xba9000, 7356, PROT_READ|PROT_WRITE,
> > > MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xba9000
> > > close(3) = 0
> > > old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)
> > > = 0xb7f36000
> > > mprotect(0xba5000, 4096, PROT_READ) = 0
> > > mprotect(0xa7d000, 4096, PROT_READ) = 0
> > > set_thread_area({entry_number:-1 -> 6, base_addr:0xb7f36940, limit:1048575,
> > > seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1,
> > > seg_not_present:0, useable:1}) = 0
> > > munmap(0xb7f37000, 98174) = 0
> > > fstat64(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 6), ...}) = 0
> > > mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
> > > 0xb7f4e000
> > > write(1, "main start\n", 11main start
> > > ) = 11
> > > write(1, "OpenIO start\n", 13OpenIO start
> > > ) = 13
> > > open("/dev/port", O_RDWR) = -1 EACCES (Permission denied)
> > > write(1, "past open\n", 10past open
> > > ) = 10
> > > dup(2) = 3
> > > fcntl64(3, F_GETFL) = 0x8002 (flags O_RDWR|O_LARGEFILE)
> > > brk(0) = 0x9bfd000
> > > brk(0x9c1e000) = 0x9c1e000
> > > fstat64(3, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 6), ...}) = 0
> > > mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
> > > 0xb7f4d000
> > > _llseek(3, 0, 0xbffc81c0, SEEK_CUR) = -1 ESPIPE (Illegal seek)
> > > write(3, "/dev/port: Permission denied\n", 29/dev/port: Permission denied
> > > ) = 29
> > > close(3) = 0
> > > munmap(0xb7f4d000, 4096) = 0
> > > munmap(0xb7f4e000, 4096) = 0
> > > exit_group(29) = ?
> > > Process 7617 detached
> > >
> > > Thanks,
> > >
> > > Ed
> > >
> > >
> > > On 9/21/06, Jim Ockers <ockers at ockers.net> wrote:
> > > >
> > > > Hi Ed,
> > > >
> > > > > I'm trying to access the parallel port (/dev/lp0) from a non root
> > > > process.
> > > > >
> > > > > Basically I have a program that can only access the port if it runs as
> > > > root.
> > > > >
> > > > > Here's what happens when I run as root:
> > > > > root at falcon:~/src/k74- 1.0# ./pprxtx all set
> > > > > root at falcon:~/src/k74-1.0# ./pprxtx read
> > > > > 255
> > > > > root at falcon:~/src/k74-1.0# ./pprxtx all clear
> > > > > root at falcon:~/src/k74-1.0# ./pprxtx read
> > > > > 0
> > > > >
> > > > > Here's what happens when I run as a non root user (ed):
> > > > > ed at falcon:~/src/k74-1.0$ ./pprxtx all set
> > > > > /dev/port: Permission denied
> > > > > ed at falcon:~/src/k74-1.0$ ./pprxtx read
> > > > > /dev/port: Permission denied
> > > >
> > > > Could you please run your pprxtx inside strace (maybe strace -f if it
> > > > forks) and let us know what system call fails with an EPERM?
> > > >
> > > > > /dev/lp0 I thought that all I had to do was to add my non rootport user
> > > > to
> > > > > the device group (lp) in /etc/group and then that user would have
> > > > > permissions to read and write to that device.
> > > > > lp:x:7:cupsys, ed
> > > > >
> > > > > I also changed the device permissions to
> > > > > /dev:
> > > > > crw-rw-rw- 1 root lp 6, 0 2006-09-21 04:56 lp0
> > > > >
> > > > > I still can't access the port unless I run as root.
> > > > >
> > > > > If I change the /dev/port (I know,dangerously insecure) permissions to
> > > > > /dev:
> > > > > crw-rw-rw- 1 root kmem 1, 4 2006-09-21 04:56 port
> > > > >
> > > > > I then get:
> > > > > ed at falcon:~/src/k74-1.0$ ./pprxtx read
> > > > > /dev/port: Operation not permitted
> > > > > ed at falcon:~/src/k74-1.0$ ./pprxtx all set
> > > > > /dev/port: Operation not permitted
> > > >
> > > > Same for this - strace should expose the problem.
> > > >
> > > > --
> > > > Jim Ockers, P.Eng. (ockers at ockers.net)
> > > > Contact info: please see http://www.ockers.net/
> > > >
> > >
> > >
> > >
> > > --
> > > Ed
> > >
> > > ------=_Part_13109_30312243.1158856981302
> > > Content-Type: text/html; charset=ISO-8859-1
> > > Content-Transfer-Encoding: 7bit
> > > Content-Disposition: inline
> > >
> > > Jim, <br><br>I've set /dev/lp0-3 and /dev/parport0-3 up as 0x666 and added myself to the lp group in /etc/group<br><br>Check it out:<br><br>[ed at denali k74-1.0]$ strace ./k74 all set<br>execve("./k74", ["./k74", "all", "set"], [/* 30 vars */]) = 0
> > > <br>uname({sys="Linux", node="<a href="http://denali.comcast.com">denali.comcast.com</a>", ...}) = 0<br>brk(0) = 0x9bfd000<br>access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
> > > <br>open("/etc/ld.so.cache", O_RDONLY) = 3<br>fstat64(3, {st_mode=S_IFREG|0644, st_size=98174, ...}) = 0<br>old_mmap(NULL, 98174, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7f37000<br>close(3) = 0
> > > <br>open("/lib/tls/libc.so.6", O_RDONLY) = 3<br>read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\20_\251"..., 512) = 512<br>fstat64(3, {st_mode=S_IFREG|0755, st_size=1454546, ...}) = 0<br>old_mmap(0xa81000, 1219772, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xa81000
> > > <br>old_mmap(0xba5000, 16384, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x124000) = 0xba5000<br>old_mmap(0xba9000, 7356, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xba9000<br>
> > > close(3) = 0<br>old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7f36000<br>mprotect(0xba5000, 4096, PROT_READ) = 0<br>mprotect(0xa7d000, 4096, PROT_READ) = 0
> > > <br>set_thread_area({entry_number:-1 -> 6, base_addr:0xb7f36940, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0<br>munmap(0xb7f37000, 98174) = 0
> > > <br>fstat64(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 6), ...}) = 0<br>mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7f4e000<br>write(1, "main start\n", 11main start<br>) = 11
> > > <br>write(1, "OpenIO start\n", 13OpenIO start<br>) = 13<br>open("/dev/port", O_RDWR) = -1 EACCES (Permission denied)<br>write(1, "past open\n", 10past open<br>) = 10
> > > <br>dup(2) = 3<br>fcntl64(3, F_GETFL) = 0x8002 (flags O_RDWR|O_LARGEFILE)<br>brk(0) = 0x9bfd000<br>brk(0x9c1e000) = 0x9c1e000
> > > <br>fstat64(3, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 6), ...}) = 0<br>mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7f4d000<br>_llseek(3, 0, 0xbffc81c0, SEEK_CUR) = -1 ESPIPE (Illegal seek)
> > > <br>write(3, "/dev/port: Permission denied\n", 29/dev/port: Permission denied<br>) = 29<br>close(3) = 0<br>munmap(0xb7f4d000, 4096) = 0<br>munmap(0xb7f4e000, 4096) = 0
> > > <br>exit_group(29) = ?<br>Process 7617 detached<br><br>Thanks, <br><br>Ed<br><br><br><div><span class="gmail_quote">On 9/21/06, <b class="gmail_sendername">Jim Ockers</b> <<a href="mailto:ockers at ockers.net">
> > > ockers at ockers.net</a>> wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Hi Ed,<br><br>> I'm trying to access the parallel port (/dev/lp0) from a non root process.
> > > <br>><br>> Basically I have a program that can only access the port if it runs as root.<br>><br>> Here's what happens when I run as root:<br>> root at falcon:~/src/k74- 1.0# ./pprxtx all set<br>> root at falcon
> > > :~/src/k74-1.0# ./pprxtx read<br>> 255<br>> root at falcon:~/src/k74-1.0# ./pprxtx all clear<br>> root at falcon:~/src/k74-1.0# ./pprxtx read<br>> 0<br>><br>> Here's what happens when I run as a non root user (ed):
> > > <br>> ed at falcon:~/src/k74-1.0$ ./pprxtx all set<br>> /dev/port: Permission denied<br>> ed at falcon:~/src/k74-1.0$ ./pprxtx read<br>> /dev/port: Permission denied<br><br>Could you please run your pprxtx inside strace (maybe strace -f if it
> > > <br>forks) and let us know what system call fails with an EPERM?<br><br>> /dev/lp0 I thought that all I had to do was to add my non rootport user to<br>> the device group (lp) in /etc/group and then that user would have
> > > <br>> permissions to read and write to that device.<br>> lp:x:7:cupsys, ed<br>><br>> I also changed the device permissions to<br>> /dev:<br>> crw-rw-rw- 1 root lp 6, 0 2006-09-21 04:56 lp0<br>><br>
> > > > I still can't access the port unless I run as root.<br>><br>> If I change the /dev/port (I know,dangerously insecure) permissions to<br>> /dev:<br>> crw-rw-rw- 1 root kmem 1, 4 2006-09-21 04:56 port<br>
> > > ><br>> I then get:<br>> ed at falcon:~/src/k74-1.0$ ./pprxtx read<br>> /dev/port: Operation not permitted<br>> ed at falcon:~/src/k74-1.0$ ./pprxtx all set<br>> /dev/port: Operation not permitted<br><br>Same for this - strace should expose the problem.
> > > <br><br>--<br>Jim Ockers, P.Eng. (<a href="mailto:ockers at ockers.net">ockers at ockers.net</a>)<br>Contact info: please see <a href="http://www.ockers.net/">http://www.ockers.net/</a><br></blockquote></div><br><br clear="all">
> > > <br>-- <br>Ed
> > >
> > > ------=_Part_13109_30312243.1158856981302--
> > >
> >
> >
>
>
>
> --
> Ed
>
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