anonfd: Allow making anon files read-only

It seems a couple places such as arch/ia64/kernel/perfmon.c and
drivers/infiniband/core/uverbs_main.c could use anon_inode_getfile()
instead of a private pseudo-fs + alloc_file(), if only there were a way
to get a read-only file.  So provide this by having anon_inode_getfile()
create a read-only file if we pass O_RDONLY in flags.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

5 files changed, 14 insertions, 6 deletions

diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 2c994591f4d7..598237e97221 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -89,11 +89,19 @@ struct file *anon_inode_getfile(const char *name,
         struct qstr this;
         struct path path;
         struct file *file;
+        fmode_t mode;
         int error;
 
         if (IS_ERR(anon_inode_inode))
                 return ERR_PTR(-ENODEV);
 
+        switch (flags & O_ACCMODE) {
+        case O_RDONLY: mode = FMODE_READ;               break;
+        case O_WRONLY: mode = FMODE_WRITE;              break;
+        case O_RDWR:   mode = FMODE_READ | FMODE_WRITE; break;
+        default:       return ERR_PTR(-EINVAL);
+        }
+
         if (fops->owner && !try_module_get(fops->owner))
                 return ERR_PTR(-ENOENT);
 
@@ -121,13 +129,13 @@ struct file *anon_inode_getfile(const char *name,
         d_instantiate(path.dentry, anon_inode_inode);
 
         error = -ENFILE;
-        file = alloc_file(&path, FMODE_READ | FMODE_WRITE, fops);
+        file = alloc_file(&path, mode, fops);
         if (!file)
                 goto err_dput;
         file->f_mapping = anon_inode_inode->i_mapping;
 
         file->f_pos = 0;
-        file->f_flags = O_RDWR | (flags & O_NONBLOCK);
+        file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
         file->f_version = 0;
         file->private_data = priv;
 
diff --git a/fs/eventfd.c b/fs/eventfd.c
index 8b47e4200e65..d26402ff06ea 100644
--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -339,7 +339,7 @@ struct file *eventfd_file_create(unsigned int count, int flags)
         ctx->flags = flags;
 
         file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx,
-                                  flags & EFD_SHARED_FCNTL_FLAGS);
+                                  O_RDWR | (flags & EFD_SHARED_FCNTL_FLAGS));
         if (IS_ERR(file))
                 eventfd_free_ctx(ctx);
 
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 366c503f9657..bd056a5b4efc 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1206,7 +1206,7 @@ SYSCALL_DEFINE1(epoll_create1, int, flags)
          * a file structure and a free file descriptor.
          */
         error = anon_inode_getfd("[eventpoll]", &eventpoll_fops, ep,
-                                 flags & O_CLOEXEC);
+                                 O_RDWR | (flags & O_CLOEXEC));
         if (error < 0)
                 ep_free(ep);
 
diff --git a/fs/signalfd.c b/fs/signalfd.c
index b07565c94386..1dabe4ee02fe 100644
--- a/fs/signalfd.c
+++ b/fs/signalfd.c
@@ -236,7 +236,7 @@ SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
                  * anon_inode_getfd() will install the fd.
                  */
                 ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
-                                       flags & (O_CLOEXEC | O_NONBLOCK));
+                                       O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
                 if (ufd < 0)
                         kfree(ctx);
         } else {
diff --git a/fs/timerfd.c b/fs/timerfd.c
index b042bd7034b1..1bfc95ad5f71 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -200,7 +200,7 @@ SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
         hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
 
         ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
-                               flags & TFD_SHARED_FCNTL_FLAGS);
+                               O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
         if (ufd < 0)
                 kfree(ctx);