eCryptfs: Privileged kthread for lower file opens

eCryptfs would really like to have read-write access to all files in the
lower filesystem.  Right now, the persistent lower file may be opened
read-only if the attempt to open it read-write fails.  One way to keep
from having to do that is to have a privileged kthread that can open the
lower persistent file on behalf of the user opening the eCryptfs file;
this patch implements this functionality.

This patch will properly allow a less-privileged user to open the eCryptfs
file, followed by a more-privileged user opening the eCryptfs file, with
the first user only being able to read and the second user being able to
both read and write.  eCryptfs currently does this wrong; it will wind up
calling vfs_write() on a file that was opened read-only.  This is fixed in
this patch.

Signed-off-by: Michael Halcrow <mhalcrow@us.ibm.com>
Cc: Dave Kleikamp <shaggy@austin.ibm.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Cc: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 19 insertions, 0 deletions

diff --git a/fs/ecryptfs/ecryptfs_kernel.h b/fs/ecryptfs/ecryptfs_kernel.h
index c15c257..b4a0ccc 100644
--- a/fs/ecryptfs/ecryptfs_kernel.h
+++ b/fs/ecryptfs/ecryptfs_kernel.h
@@ -559,6 +559,20 @@ extern struct kmem_cache *ecryptfs_key_record_cache;
 extern struct kmem_cache *ecryptfs_key_sig_cache;
 extern struct kmem_cache *ecryptfs_global_auth_tok_cache;
 extern struct kmem_cache *ecryptfs_key_tfm_cache;
+extern struct kmem_cache *ecryptfs_open_req_cache;
+
+struct ecryptfs_open_req {
+#define ECRYPTFS_REQ_PROCESSED 0x00000001
+#define ECRYPTFS_REQ_DROPPED   0x00000002
+#define ECRYPTFS_REQ_ZOMBIE    0x00000004
+	u32 flags;
+	struct file **lower_file;
+	struct dentry *lower_dentry;
+	struct vfsmount *lower_mnt;
+	wait_queue_head_t wait;
+	struct mutex mux;
+	struct list_head kthread_ctl_list;
+};
 
 int ecryptfs_interpose(struct dentry *hidden_dentry,
 		       struct dentry *this_dentry, struct super_block *sb,
@@ -690,5 +704,10 @@ void ecryptfs_msg_ctx_alloc_to_free(struct ecryptfs_msg_ctx *msg_ctx);
 int
 ecryptfs_spawn_daemon(struct ecryptfs_daemon **daemon, uid_t euid,
 		      struct user_namespace *user_ns, struct pid *pid);
+int ecryptfs_init_kthread(void);
+void ecryptfs_destroy_kthread(void);
+int ecryptfs_privileged_open(struct file **lower_file,
+			     struct dentry *lower_dentry,
+			     struct vfsmount *lower_mnt);
 
 #endif /* #ifndef ECRYPTFS_KERNEL_H */