Messages in this thread | | | Date | Sun, 29 Jan 2012 14:19:20 +0000 | From | Alan Cox <> | Subject | Re: /proc/[pid]/mem write implications |
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> > But I think that allowing arbitrary processes to write to **their own** > > memory via a file descriptor might in itself be problematic. Please, > > help me understand how this is safe. > > You will have a sysctl to control if it is writable.
The problem is not that the check is done in write, the problem is more fundamental - the open should bind to the memory of the executable image currently running, instead it effectively late binds each write to the image now being run. That is the root cause.
What's sad about this is that people went and re-introduced the bug and clearly didn't think to spend 2 minutes asking Google why the checks were there originally.
2006 thread
http://lkml.indiana.edu/hypermail/linux/kernel/0605.2/1359.html
2004 thread
http://lkml.indiana.edu/hypermail/linux/kernel/0407.0/1169.html
2002 thread
http://www.eros-os.org/pipermail/cap-talk/2002-May/000922.html
If you really want to fix this then you need to bind /proc/self/mem to the executable image in question, and you need to effectively revoke() that on exec so it can't be used to pin old images into memory.
Fix that and the rest falls out in the wash.
Alan
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