On Sat, May 26, 2018 at 07:30:47PM +0200, Salvatore Mesoraca wrote: > 2018-05-26 17:48 GMT+02:00 Alexey Dobriyan <adobriyan@xxxxxxxxx>: > > On Sat, May 26, 2018 at 04:50:46PM +0200, Salvatore Mesoraca wrote: > >> Prevent a task from opening, in "write" mode, any /proc/*/mem > >> file that operates on the task's mm. > >> /proc/*/mem is mainly a debugging means and, as such, it shouldn't > >> be used by the inspected process itself. > >> Current implementation always allow a task to access its own > >> /proc/*/mem file. > >> A process can use it to overwrite read-only memory, making > >> pointless the use of security_file_mprotect() or other ways to > >> enforce RO memory. > > > > You can do it in security_ptrace_access_check() > > No, because that hook is skipped when mm == current->mm: > https://elixir.bootlin.com/linux/v4.17-rc6/source/kernel/fork.c#L1111 OK > > or security_file_open() > > This is true, but it looks a bit overkill to me, especially since many of > the macros/functions used to handle proc's files won't be in scope > for an external LSM. > Is there any particular reason why you prefer it done via LSM? Well, it exists to implement all kinds of non-standard restrictions. You're probably blacklisting mprotect() and worry that compromised program might use /proc/self/mem instead. But you need to blacklist much more that mprotect(). I think forking a dummy "worker" process to open your /proc/*/mem and pass a descriptor back should still work with your patch.
