Messages in this thread | | | Date | Thu, 29 Jan 2015 17:31:12 -0800 | Subject | Re: [PATCH] docs: procs -- Describe /proc/<pid>/map_files entry | From | Kees Cook <> |
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On Tue, Jan 27, 2015 at 1:20 PM, Cyrill Gorcunov <gorcunov@gmail.com> wrote: > On Tue, Jan 27, 2015 at 11:50:49AM -0800, Kees Cook wrote: >> > + >> > +The main purpose of map_files directory is to be able to retrieve a set of >> > +memory mapped files in a fast way instead of parsing /proc/<pid>/maps or >> > +/proc/<pid>/smaps which contain a way more records. Same time one can open(2) >> > +mappings from the listings of two processes and comparing inodes figure out >> > +which anonymous memory areas are actually shared. >> >> Thanks for details! I still don't understand how this is used for >> checkpoint/restore when the mmap offset isn't shown. Can't a process >> map, say 4K of a file, from different offsets, and it would show up >> as: >> >> 400000-401000 -> /some/file >> 401000-402000 -> /some/file >> >> but there'd be no way to know how to restore that mapping? > > In criu we use a few sources of information (ie we scan not only > map_files, but have to use /proc/pid/smaps as well which has > offset for mapping). So at the end we have all picture under > our hands. > >> Are these symlinks "regular" symlinks, or are they something more >> special that bypasses VFS? If it bypasses VFS, I think adding and open >> check with PTRACE_ATTACH is needed, since now you're able to _modify_ >> the memory space of the target process instead of just reading it. > > Opening them goes same way as open of /proc/pid/fd/ entries as > far as I can tell. This should be enough, or I miss something > obvious here? Otherwise opening /proc/pid/fd/ should use > PTRACE_ATTACH instead of PTRACE_MODE_READ (as in proc_fd_access_allowed).
I wouldn't object to enhancing the check to ATTACH from READ, but I worry what would break on the existing interface.
-Kees
-- Kees Cook Chrome OS Security
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