proc 1/2: do PDE usecounting even for ->read_proc, ->write_proc

struct proc_dir_entry::owner is going to be removed. Now it's only necessary
to protect PDEs which are using ->read_proc, ->write_proc hooks.

However, ->owner assignments are racy and make it very easy for someone to switch
->owner on live PDE (as some subsystems do) without fixing refcounts and so on.

http://bugzilla.kernel.org/show_bug.cgi?id=12454

So, ->owner is on death row.

Proxy file operations exist already (proc_file_operations), just bump usecount
when necessary.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 8c68bbe..fa678ab 100644 (file)
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -37,7 +37,7 @@ static int proc_match(int len, const char *name, struct proc_dir_entry *de)
 #define PROC_BLOCK_SIZE        (PAGE_SIZE - 1024)
 
 static ssize_t
-proc_file_read(struct file *file, char __user *buf, size_t nbytes,
+__proc_file_read(struct file *file, char __user *buf, size_t nbytes,
               loff_t *ppos)
 {
        struct inode * inode = file->f_path.dentry->d_inode;
@@ -182,20 +182,48 @@ proc_file_read(struct file *file, char __user *buf, size_t nbytes,
        return retval;
 }
 
+static ssize_t
+proc_file_read(struct file *file, char __user *buf, size_t nbytes,
+              loff_t *ppos)
+{
+       struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
+       ssize_t rv = -EIO;
+
+       spin_lock(&pde->pde_unload_lock);
+       if (!pde->proc_fops) {
+               spin_unlock(&pde->pde_unload_lock);
+               return rv;
+       }
+       pde->pde_users++;
+       spin_unlock(&pde->pde_unload_lock);
+
+       rv = __proc_file_read(file, buf, nbytes, ppos);
+
+       pde_users_dec(pde);
+       return rv;
+}
+
 static ssize_t
 proc_file_write(struct file *file, const char __user *buffer,
                size_t count, loff_t *ppos)
 {
-       struct inode *inode = file->f_path.dentry->d_inode;
-       struct proc_dir_entry * dp;
-       
-       dp = PDE(inode);
-
-       if (!dp->write_proc)
-               return -EIO;
+       struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
+       ssize_t rv = -EIO;
+
+       if (pde->write_proc) {
+               spin_lock(&pde->pde_unload_lock);
+               if (!pde->proc_fops) {
+                       spin_unlock(&pde->pde_unload_lock);
+                       return rv;
+               }
+               pde->pde_users++;
+               spin_unlock(&pde->pde_unload_lock);
 
-       /* FIXME: does this routine need ppos?  probably... */
-       return dp->write_proc(file, buffer, count, dp->data);
+               /* FIXME: does this routine need ppos?  probably... */
+               rv = pde->write_proc(file, buffer, count, pde->data);
+               pde_users_dec(pde);
+       }
+       return rv;
 }
 
 

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index d8bb5c6..e11dc22 100644 (file)
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -127,7 +127,7 @@ static void __pde_users_dec(struct proc_dir_entry *pde)
                complete(pde->pde_unload_completion);
 }
 
-static void pde_users_dec(struct proc_dir_entry *pde)
+void pde_users_dec(struct proc_dir_entry *pde)
 {
        spin_lock(&pde->pde_unload_lock);
        __pde_users_dec(pde);

diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index cd53ff8..f6db961 100644 (file)
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -91,3 +91,4 @@ struct pde_opener {
        int (*release)(struct inode *, struct file *);
        struct list_head lh;
 };
+void pde_users_dec(struct proc_dir_entry *pde);