Re: [PATCH] security: split proc ptrace checking into read vs. attach

[Chris Wright <chrisw@sous-sol.org>]

* Stephen Smalley (sds@tycho.nsa.gov) wrote:
> Enable security modules to distinguish reading of process state via
> proc from full ptrace access by renaming ptrace_may_attach to
> ptrace_may_access and adding a mode argument indicating whether only
> read access or full attach access is requested.  This allows security
> modules to permit access to reading process state without granting
> full ptrace access.  The base DAC/capability checking remains unchanged.
> 
> Read access to /proc/pid/mem continues to apply a full ptrace attach
> check since check_mem_permission() already requires the current task
> to already be ptracing the target.  The other ptrace checks within
> proc for elements like environ, maps, and fds are changed to pass the
> read mode instead of attach.
> 
> In the SELinux case, we model such reading of process state as a
> reading of a proc file labeled with the target process' label.  This
> enables SELinux policy to permit such reading of process state without
> permitting control or manipulation of the target process, as there are
> a number of cases where programs probe for such information via proc
> but do not need to be able to control the target (e.g. procps,
> lsof, PolicyKit, ConsoleKit).  At present we have to choose between
> allowing full ptrace in policy (more permissive than required/desired)
> or breaking functionality (or in some cases just silencing the denials
> via dontaudit rules but this can hide genuine attacks).
> 
> This version of the patch incorporates comments from Casey Schaufler
> (change/replace existing ptrace_may_attach interface, pass access
> mode), and Chris Wright (provide greater consistency in the checking).
> 
> Note that like their predecessors __ptrace_may_attach and
> ptrace_may_attach, the __ptrace_may_access and ptrace_may_access
> interfaces use different return value conventions from each other (0
> or -errno vs. 1 or 0).  I retained this difference to avoid any
> changes to the caller logic but made the difference clearer by
> changing the latter interface to return a bool rather than an int and
> by adding a comment about it to ptrace.h for any future callers.
> 
> Signed-off-by:  Stephen Smalley <sds@tycho.nsa.gov>

Acked-by: Chris Wright <chrisw@sous-sol.org>