Messages in this thread | | | Date | Wed, 1 Dec 2004 01:00:13 +0000 (GMT) | From | Hugh Dickins <> | Subject | Re: [PATCH] shmtcl SHM_LOCK perms |
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On Tue, 30 Nov 2004, Chris Wright wrote: > * Hugh Dickins (hugh@veritas.com) wrote: > > Michael Kerrisk has observed that at present any process can SHM_LOCK > > any shm segment of size within process RLIMIT_MEMLOCK, despite having no > > permissions on the segment: surprising, though not obviously evil. And > > any process can SHM_UNLOCK any shm segment, despite no permissions on it: > > that is surely wrong. > > You may be neither the owner, nor the creator of a segment but have read > access to it. In which case you could simply copy the contents of the > segment anywhere you like, which has similar effect to SHM_UNLOCK from > the point of view of paging out sensitive data.
True, and if securing sensitive data against pageout were the only reason for SHM_LOCK, then I guess it might be an argument for letting anyone with read permission do SHM_UNLOCK.
But that's not the only reason for SHM_LOCK, and all you're telling us there is that the owner of sensitive data should be careful who they give read permission to - indeed! So I still tend to agree with Michael, that the most natural restriction is to owner or creator - relax that if some app actually has a good case for relaxing it.
Hugh
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