Joakim Tjernlund/Transmode wrote on 2014/07/18 15:49:17:
>
> Richard Weinberger <[email protected]> wrote on 2014/07/18
14:58:30:
> >
> > On Thu, Jul 17, 2014 at 1:18 PM, Joakim Tjernlund
> > <[email protected]> wrote:
> > > Trying to real /proc/<pid>/exe I noticed I could not read links not
> > > belonging to my user such as:
> > > jocke > ls -l /proc/1/exe
> > > ls: cannot read symbolic link /proc/1/exe: Permission
denied
> > >
> > > Is this expected?
> >
> > Why do you think this is unexpected?
> It only shows the full path to the executable, compare with comm which
shows basename(app).
>
> I have an idea for qemu-user which needs to identify which processes
> are running /usr/bin/qemu-<arch> and which are not so it knows how
> to munge different /proc/ files.
Just to be clear, I expect to read where /proc/1/exe points, not the
contents of the file
pointed to.
It seems that any and all symlinks are forbidden:
> ls -l /proc/1
ls: cannot read symbolic link /proc/1/cwd: Permission denied
ls: cannot read symbolic link /proc/1/root: Permission denied
ls: cannot read symbolic link /proc/1/exe: Permission denied
Jocke
Am 18.07.2014 17:05, schrieb Joakim Tjernlund:
> Joakim Tjernlund/Transmode wrote on 2014/07/18 15:49:17:
>>
>> Richard Weinberger <[email protected]> wrote on 2014/07/18
> 14:58:30:
>>>
>>> On Thu, Jul 17, 2014 at 1:18 PM, Joakim Tjernlund
>>> <[email protected]> wrote:
>>>> Trying to real /proc/<pid>/exe I noticed I could not read links not
>>>> belonging to my user such as:
>>>> jocke > ls -l /proc/1/exe
>>>> ls: cannot read symbolic link /proc/1/exe: Permission
> denied
>>>>
>>>> Is this expected?
>>>
>>> Why do you think this is unexpected?
>
>> It only shows the full path to the executable, compare with comm which
> shows basename(app).
>>
>> I have an idea for qemu-user which needs to identify which processes
>> are running /usr/bin/qemu-<arch> and which are not so it knows how
>> to munge different /proc/ files.
>
> Just to be clear, I expect to read where /proc/1/exe points, not the
> contents of the file
> pointed to.
>
> It seems that any and all symlinks are forbidden:
>> ls -l /proc/1
> ls: cannot read symbolic link /proc/1/cwd: Permission denied
> ls: cannot read symbolic link /proc/1/root: Permission denied
> ls: cannot read symbolic link /proc/1/exe: Permission denied
Because they all share the same implementation.
See proc_pid_link_inode_operations() in fs/proc/base.c
Happy hacking. :-)
Thanks,
//richard