linux-kernel - Re: procfs: introduce the /proc/<pid>/map

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Date:	Tue, 20 Mar 2012 15:18:16 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Jan Engelhardt <jengelh@...ozas.de>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: procfs: introduce the /proc/<pid>/map_files/ directory

On 03/19/2012 09:19 PM, Jan Engelhardt wrote:
> Hi,
> 
> 
> I tried out the map_files directory in v3.3, stumbling upon a few 
> things:
> 
> /proc> echo $$
> 1724
> /proc> cd 1724/map_files/
> /proc/1724/map_files> ls
> ls: reading directory .: Permission denied
> /proc/1724/map_files> ls -dl .
> dr-x------ 2 jengelh users 0 Mar 19 12:54 .
> 
> By all means, I have the permission - according to stat.

All this code is CAP_SYS_ADMIN protected.

> Also, not all mappings - in particular, anonymous mappings - seem to be 
> represented:
> 
> 00400000-0049b000 r-xp 00000000 08:02 10425                              /bin/ba
> 0069a000-0069b000 r--p 0009a000 08:02 10425                              /bin/ba
> 0069b000-0069f000 rw-p 0009b000 08:02 10425                              /bin/ba
> 0069f000-006a9000 rw-p 00000000 00:00 0 
> 01a90000-01bf8000 rw-p 00000000 00:00 0                                  [heap]
> 7f87eb3be000-7f87eb559000 r-xp 00000000 08:02 980                        /lib64/
> 7f87eb559000-7f87eb758000 ---p 0019b000 08:02 980                        /lib64/
> 7f87eb758000-7f87eb75c000 r--p 0019a000 08:02 980                        /lib64/
> 7f87eb75c000-7f87eb75e000 rw-p 0019e000 08:02 980                        /lib64/
> 7f87eb75e000-7f87eb762000 rw-p 00000000 00:00 0 
> [...]
> 7f87ebffd000-7f87ebffe000 rw-p 00021000 08:02 71                         /lib64/ld-2.15.so
> 7f87ebffe000-7f87ebfff000 rw-p 00000000 00:00 0
> 7fffb9f1e000-7fffb9f3f000 rw-p 00000000 00:00 0                          [stack]
> 7fffb9fb5000-7fffb9fb6000 r-xp 00000000 00:00 0                          [vdso]
> ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]
> 
> /proc/1724/map_files # ls -alog
> total 0
> dr-x------ 2  0 Mar 19 12:54 .
> dr-xr-xr-x 9  0 Mar 19 12:54 ..
> lr-------- 1 64 Mar 19 12:54 400000-49b000 -> /bin/bash
> lr-------- 1 64 Mar 19 12:54 69a000-69b000 -> /bin/bash
> lr-------- 1 64 Mar 19 12:54 69b000-69f000 -> /bin/bash
> lr-------- 1 64 Mar 19 12:54 7f87eb3be000-7f87eb559000 -> /lib64/libc-2.15.so
> lr-------- 1 64 Mar 19 12:54 7f87eb559000-7f87eb758000 -> /lib64/libc-2.15.so
> lr-------- 1 64 Mar 19 12:54 7f87eb758000-7f87eb75c000 -> /lib64/libc-2.15.so
> lr-------- 1 64 Mar 19 12:54 7f87eb75c000-7f87eb75e000 -> /lib64/libc-2.15.so
> lr-------- 1 64 Mar 19 12:54 7f87eb762000-7f87eb764000 -> /lib64/libdl-2.15.so
> lr-------- 1 64 Mar 19 12:54 7f87eb764000-7f87eb964000 -> /lib64/libdl-2.15.so
> lr-------- 1 64 Mar 19 12:54 7f87eb964000-7f87eb965000 -> /lib64/libdl-2.15.so
> lr-------- 1 64 Mar 19 12:54 7f87eb965000-7f87eb966000 -> /lib64/libdl-2.15.so
> lr-------- 1 64 Mar 19 12:54 7f87eb966000-7f87eb98f000 -> /lib64/libtinfo.so.5.9
> lr-------- 1 64 Mar 19 12:54 7f87eb98f000-7f87ebb8e000 -> /lib64/libtinfo.so.5.9
> lr-------- 1 64 Mar 19 12:54 7f87ebb8e000-7f87ebb92000 -> /lib64/libtinfo.so.5.9
> lr-------- 1 64 Mar 19 12:54 7f87ebb92000-7f87ebb97000 -> /lib64/libtinfo.so.5.9
> lr-------- 1 64 Mar 19 12:54 7f87ebb98000-7f87ebbd3000 -> /lib64/libreadline.so.6.2
> lr-------- 1 64 Mar 19 12:54 7f87ebbd3000-7f87ebdd3000 -> /lib64/libreadline.so.6.2
> lr-------- 1 64 Mar 19 12:54 7f87ebdd3000-7f87ebdd5000 -> /lib64/libreadline.so.6.2
> lr-------- 1 64 Mar 19 12:54 7f87ebdd5000-7f87ebddb000 -> /lib64/libreadline.so.6.2
> lr-------- 1 64 Mar 19 12:54 7f87ebddc000-7f87ebdfd000 -> /lib64/ld-2.15.so
> lr-------- 1 64 Mar 19 12:54 7f87ebffc000-7f87ebffd000 -> /lib64/ld-2.15.so
> lr-------- 1 64 Mar 19 12:54 7f87ebffd000-7f87ebffe000 -> /lib64/ld-2.15.so
> 
> Having symlinks into anonmaps would provide for an interesting type
> of debug/insight without having to resort to ptracting, just as
> /proc/X/fd/Y is when the file behind Y is nlink=0.
> .

What should happen when you try to open() this link?
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