question about /proc/<PID>/mem in 2.4

[Tigran Aivazian]

Hello,

I noticed that in 2.4.x kernels the fs/proc/base.c:mem_read() function has 
this permission check:

        if (!MAY_PTRACE(task) || !may_ptrace_attach(task))
                return -ESRCH;

Are you sure it shouldn't be like this instead:

        if (!MAY_PTRACE(task) && !may_ptrace_attach(task))
                return -ESRCH;

Because, normally MAY_PTRACE() is 0 (i.e. for any process worth looking at :)
so may_ptrace_attach() is never even called.

Is there any reason for the above check on each read(2)? Shouldn't there 
be a simple check at ->open() time only? I assume this is to close some 
obscure "security hole" but I would like to see the explanation of how 
could any problem arise if a) such check wasn't done at all (except at 
open(2) time) or at least b) there was && instead of ||.

The 2.6.x situation is similar except the addition of the security stuff.

Kind regards
Tigran

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