[PATCH] epoll: fix delayed initialization bug

Al found a potential problem in epoll_create(), where the
file->private_data member was set after fd_install().  This is obviously
wrong since another thread might do a close() on that fd# before we set the
file->private_data member.  This goes over 2.6.13 and passes a few basic
tests I've done here.

(akpm: snuck in a kzalloc() cleanup too)

Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 6ab1dd0..403b90a 100644 (file)
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -231,8 +231,9 @@ struct ep_pqueue {
 
 static void ep_poll_safewake_init(struct poll_safewake *psw);
 static void ep_poll_safewake(struct poll_safewake *psw, wait_queue_head_t *wq);
-static int ep_getfd(int *efd, struct inode **einode, struct file **efile);
-static int ep_file_init(struct file *file);
+static int ep_getfd(int *efd, struct inode **einode, struct file **efile,
+                   struct eventpoll *ep);
+static int ep_alloc(struct eventpoll **pep);
 static void ep_free(struct eventpoll *ep);
 static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd);
 static void ep_use_epitem(struct epitem *epi);
@@ -501,38 +502,37 @@ void eventpoll_release_file(struct file *file)
 asmlinkage long sys_epoll_create(int size)
 {
        int error, fd;
+       struct eventpoll *ep;
        struct inode *inode;
        struct file *file;
 
        DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d)\n",
                     current, size));
 
-       /* Sanity check on the size parameter */
+       /*
+        * Sanity check on the size parameter, and create the internal data
+        * structure ( "struct eventpoll" ).
+        */
        error = -EINVAL;
-       if (size <= 0)
+       if (size <= 0 || (error = ep_alloc(&ep)) != 0)
                goto eexit_1;
 
        /*
         * Creates all the items needed to setup an eventpoll file. That is,
         * a file structure, and inode and a free file descriptor.
         */
-       error = ep_getfd(&fd, &inode, &file);
-       if (error)
-               goto eexit_1;
-
-       /* Setup the file internal data structure ( "struct eventpoll" ) */
-       error = ep_file_init(file);
+       error = ep_getfd(&fd, &inode, &file, ep);
        if (error)
                goto eexit_2;
 
-
        DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d) = %d\n",
                     current, size, fd));
 
        return fd;
 
 eexit_2:
-       sys_close(fd);
+       ep_free(ep);
+       kfree(ep);
 eexit_1:
        DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d) = %d\n",
                     current, size, error));
@@ -706,7 +706,8 @@ eexit_1:
 /*
  * Creates the file descriptor to be used by the epoll interface.
  */
-static int ep_getfd(int *efd, struct inode **einode, struct file **efile)
+static int ep_getfd(int *efd, struct inode **einode, struct file **efile,
+                   struct eventpoll *ep)
 {
        struct qstr this;
        char name[32];
@@ -756,7 +757,7 @@ static int ep_getfd(int *efd, struct inode **einode, struct file **efile)
        file->f_op = &eventpoll_fops;
        file->f_mode = FMODE_READ;
        file->f_version = 0;
-       file->private_data = NULL;
+       file->private_data = ep;
 
        /* Install the new setup file into the allocated fd. */
        fd_install(fd, file);
@@ -777,14 +778,13 @@ eexit_1:
 }
 
 
-static int ep_file_init(struct file *file)
+static int ep_alloc(struct eventpoll **pep)
 {
-       struct eventpoll *ep;
+       struct eventpoll *ep = kzalloc(sizeof(*ep), GFP_KERNEL);
 
-       if (!(ep = kmalloc(sizeof(struct eventpoll), GFP_KERNEL)))
+       if (!ep)
                return -ENOMEM;
 
-       memset(ep, 0, sizeof(*ep));
        rwlock_init(&ep->lock);
        init_rwsem(&ep->sem);
        init_waitqueue_head(&ep->wq);
@@ -792,9 +792,9 @@ static int ep_file_init(struct file *file)
        INIT_LIST_HEAD(&ep->rdllist);
        ep->rbr = RB_ROOT;
 
-       file->private_data = ep;
+       *pep = ep;
 
-       DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_file_init() ep=%p\n",
+       DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_alloc() ep=%p\n",
                     current, ep));
        return 0;
 }