device-dax: fix private mapping restriction, permit read-only
authorDan Williams <dan.j.williams@intel.com>
Wed, 7 Dec 2016 01:03:35 +0000 (17:03 -0800)
committerDan Williams <dan.j.williams@intel.com>
Wed, 7 Dec 2016 01:42:37 +0000 (17:42 -0800)
commit325896ffdf90f7cbd59fb873b7ba20d60d1ddf3c
treed71d337b3a5b9858907c6a4a0797ced074302590
parenta7de92dac9f0dbf01deb56fe1d661d7baac097e1
device-dax: fix private mapping restriction, permit read-only

Hugh notes in response to commit 4cb19355ea19 "device-dax: fail all
private mapping attempts":

  "I think that is more restrictive than you intended: haven't tried, but I
  believe it rejects a PROT_READ, MAP_SHARED, O_RDONLY fd mmap, leaving no
  way to mmap /dev/dax without write permission to it."

Indeed it does restrict read-only mappings, switch to checking
VM_MAYSHARE, not VM_SHARED.

Cc: <stable@vger.kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Pawel Lebioda <pawel.lebioda@intel.com>
Fixes: 4cb19355ea19 ("device-dax: fail all private mapping attempts")
Reported-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
drivers/dax/dax.c