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Re: [PATCH v2] gdbserver: linux_low: elf_64_file_p cache results


On 08/24/2017 03:42 PM, Pedro Alves wrote:

> I'm still mystified about why can't gdbserver read
> the file after "droproot" has changed user.
> I assume gdbserver is running as root?  Why wouldn't
> a gdbserver running as root be able to read "jringle"'s
> /proc file?
> 
> Does CAP_PTRACE make a difference?

FAOD, I meant CAP_SYS_PTRACE.

See for example here:
http://man7.org/linux/man-pages/man5/proc.5.html

~~~
/proc/[pid]/exe
...
              Permission to dereference or read (readlink(2)) this symbolic
              link is governed by a ptrace access mode
              PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
~~~

[and follow on to ptrace(2).]

> 
> I have to wonder whether there's a better way to do this..
> gdbserver needs to read other /proc files, some not cacheable.
> I fear that you may have run into just one case so far, and
> that we may run into problems if we take this route.

Thanks,
Pedro Alves


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