[PATCH 0/6] enable writing to /proc/pid/mem

[Stephen Wilson]

For a long time /proc/pid/mem has provided a read-only interface, at least
since 2.4.0.  However, a write capability has existed "forever" in tree via the
function mem_write(), disabled with an #ifdef along with the comment "this is a
security hazard".  Currently, the main problem with mem_write() is that between
the time permissions are checked and the actual write the target task could
exec a setuid-root binary.

This patch series enables safe writes to /proc/pid/mem.  The principle strategy
is to get a reference to the target task's mm before the permission check, and
to hold that reference until after the write completes.

This patch is useful as it gives debuggers a simple and efficient mechanism to
manipulate a processes address space.  Memory can be read and written using
single calls to pread(2) and pwrite(2) instead of iteratively calling
into ptrace(2).  In addition, /proc/pid/mem has always had write permissions
enabled, so clearly it *wants* to be written to. 

This series builds off previous work up for review here:

   http://lkml.org/lkml/2011/3/8/409

The general approach used was suggested to me by Alexander Viro, but any
mistakes present in these patches are entirely my own.


--
steve


Stephen Wilson (6):
      mm: use mm_struct to resolve gate vma's in __get_user_pages
      mm: factor out main logic of access_process_vm
      mm: implement access_remote_vm
      proc: disable mem_write after exec
      proc: make check_mem_permission() return an mm_struct on success
      proc: enable writing to /proc/pid/mem


 fs/proc/base.c     |   61 ++++++++++++++++++++++++++-------------------
 include/linux/mm.h |    2 +
 mm/memory.c        |   69 +++++++++++++++++++++++++++++++++++++++-------------
 3 files changed, 89 insertions(+), 43 deletions(-)



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