fs: introduce f_op->mmap_capabilities for nommu mmap support

Since "BDI: Provide backing device capability information [try #3]" the
backing_dev_info structure also provides flags for the kind of mmap
operation available in a nommu environment, which is entirely unrelated
to it's original purpose.

Introduce a new nommu-only file operation to provide this information to
the nommu mmap code instead.  Splitting this from the backing_dev_info
structure allows to remove lots of backing_dev_info instance that aren't
otherwise needed, and entirely gets rid of the concept of providing a
backing_dev_info for a character device.  It also removes the need for
the mtd_inodefs filesystem.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Tejun Heo <tj@kernel.org>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 6 insertions, 7 deletions

diff --git a/security/security.c b/security/security.c
index 18b35c63fc0c..a0442b20f001 100644
--- a/security/security.c
+++ b/security/security.c
@@ -726,16 +726,15 @@ static inline unsigned long mmap_prot(struct file *file, unsigned long prot)
                 return prot | PROT_EXEC;
         /*
          * ditto if it's not on noexec mount, except that on !MMU we need
-         * BDI_CAP_EXEC_MMAP (== VM_MAYEXEC) in this case
+         * NOMMU_MAP_EXEC (== VM_MAYEXEC) in this case
          */
         if (!(file->f_path.mnt->mnt_flags & MNT_NOEXEC)) {
 #ifndef CONFIG_MMU
-                unsigned long caps = 0;
-                struct address_space *mapping = file->f_mapping;
-                if (mapping && mapping->backing_dev_info)
-                        caps = mapping->backing_dev_info->capabilities;
-                if (!(caps & BDI_CAP_EXEC_MAP))
-                        return prot;
+                if (file->f_op->mmap_capabilities) {
+                        unsigned caps = file->f_op->mmap_capabilities(file);
+                        if (!(caps & NOMMU_MAP_EXEC))
+                                return prot;
+                }
 #endif
                 return prot | PROT_EXEC;
         }