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authorDavid Herrmann <dh.herrmann@gmail.com>2014-08-08 14:25:25 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-08-08 15:57:31 -0700
commit4bb5f5d9395bc112d93a134d8f5b05611eddc9c0 (patch)
tree68af5a8a8cc65375c51c25bff678d0f9825d86af /include/linux/fs.h
parent935e9f02e798051d2923d59f6025cd74f59aa0e1 (diff)
mm: allow drivers to prevent new writable mappings
This patch (of 6): The i_mmap_writable field counts existing writable mappings of an address_space. To allow drivers to prevent new writable mappings, make this counter signed and prevent new writable mappings if it is negative. This is modelled after i_writecount and DENYWRITE. This will be required by the shmem-sealing infrastructure to prevent any new writable mappings after the WRITE seal has been set. In case there exists a writable mapping, this operation will fail with EBUSY. Note that we rely on the fact that iff you already own a writable mapping, you can increase the counter without using the helpers. This is the same that we do for i_writecount. Signed-off-by: David Herrmann <dh.herrmann@gmail.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Ryan Lortie <desrt@desrt.ca> Cc: Lennart Poettering <lennart@poettering.net> Cc: Daniel Mack <zonque@gmail.com> Cc: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/fs.h')
-rw-r--r--include/linux/fs.h29
1 files changed, 27 insertions, 2 deletions
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 1ab6c6913040..f0890e4a7c25 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -387,7 +387,7 @@ struct address_space {
struct inode *host; /* owner: inode, block_device */
struct radix_tree_root page_tree; /* radix tree of all pages */
spinlock_t tree_lock; /* and lock protecting it */
- unsigned int i_mmap_writable;/* count VM_SHARED mappings */
+ atomic_t i_mmap_writable;/* count VM_SHARED mappings */
struct rb_root i_mmap; /* tree of private and shared mappings */
struct list_head i_mmap_nonlinear;/*list VM_NONLINEAR mappings */
struct mutex i_mmap_mutex; /* protect tree, count, list */
@@ -470,10 +470,35 @@ static inline int mapping_mapped(struct address_space *mapping)
* Note that i_mmap_writable counts all VM_SHARED vmas: do_mmap_pgoff
* marks vma as VM_SHARED if it is shared, and the file was opened for
* writing i.e. vma may be mprotected writable even if now readonly.
+ *
+ * If i_mmap_writable is negative, no new writable mappings are allowed. You
+ * can only deny writable mappings, if none exists right now.
*/
static inline int mapping_writably_mapped(struct address_space *mapping)
{
- return mapping->i_mmap_writable != 0;
+ return atomic_read(&mapping->i_mmap_writable) > 0;
+}
+
+static inline int mapping_map_writable(struct address_space *mapping)
+{
+ return atomic_inc_unless_negative(&mapping->i_mmap_writable) ?
+ 0 : -EPERM;
+}
+
+static inline void mapping_unmap_writable(struct address_space *mapping)
+{
+ atomic_dec(&mapping->i_mmap_writable);
+}
+
+static inline int mapping_deny_writable(struct address_space *mapping)
+{
+ return atomic_dec_unless_positive(&mapping->i_mmap_writable) ?
+ 0 : -EBUSY;
+}
+
+static inline void mapping_allow_writable(struct address_space *mapping)
+{
+ atomic_inc(&mapping->i_mmap_writable);
}
/*