Messages in this thread | | | Date | Wed, 6 Aug 2014 13:05:06 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH v2 4/7] fs/proc/task_mmu.c: shift mm_access() from m_start() to proc_maps_open() |
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On Tue, Aug 05, 2014 at 09:46:55PM +0200, Oleg Nesterov wrote: > A simple test-case from Kirill Shutemov > > cat /proc/self/maps >/dev/null > chmod +x /proc/self/net/packet > exec /proc/self/net/packet > > makes lockdep unhappy, cat/exec take seq_file->lock + cred_guard_mutex in > the opposite order. > > It's a false positive and probably we should not allow "chmod +x" on proc > files. Still I think that we should avoid mm_access() and cred_guard_mutex > in sys_read() paths, security checking should happen at open time. Besides, > this doesn't even look right if the task changes its ->mm between m_stop() > and m_start(). > > Add the new "mm_struct *mm" member into struct proc_maps_private and change > proc_maps_open() to initialize it using proc_mem_open(). Change m_start() to > use priv->mm if atomic_inc_not_zero(mm_users) succeeds or return NULL (eof) > otherwise. > > The only complication is that proc_maps_open() users should additionally do > mmdrop() in fop->release(), add the new proc_map_release() helper for that. > > Note: this is the user-visible change, if the task execs after open("maps") > the new ->mm won't be visible via this file. I hope this is fine, and this > matches /proc/pid/mem bahaviour. > > Reported-by: "Kirill A. Shutemov" <kirill@shutemov.name> > Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> -- Kirill A. Shutemov
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