vfs: check i_nlink limits in vfs_{mkdir,rename_dir,link}

New field of struct super_block - ->s_max_links.  Maximal allowed
value of ->i_nlink or 0; in the latter case all checks still need
to be done in ->link/->mkdir/->rename instances.  Note that this
limit applies both to directoris and to non-directories.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 13 insertions, 0 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 46ea9cc16647..a0b82762e8fc 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2569,6 +2569,7 @@ SYSCALL_DEFINE3(mknod, const char __user *, filename, umode_t, mode, unsigned, d
 int vfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 {
         int error = may_create(dir, dentry);
+        unsigned max_links = dir->i_sb->s_max_links;
 
         if (error)
                 return error;
@@ -2581,6 +2582,9 @@ int vfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
         if (error)
                 return error;
 
+        if (max_links && dir->i_nlink >= max_links)
+                return -EMLINK;
+
         error = dir->i_op->mkdir(dir, dentry, mode);
         if (!error)
                 fsnotify_mkdir(dir, dentry);
@@ -2911,6 +2915,7 @@ SYSCALL_DEFINE2(symlink, const char __user *, oldname, const char __user *, newn
 int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry)
 {
         struct inode *inode = old_dentry->d_inode;
+        unsigned max_links = dir->i_sb->s_max_links;
         int error;
 
         if (!inode)
@@ -2941,6 +2946,8 @@ int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_de
         /* Make sure we don't allow creating hardlink to an unlinked file */
         if (inode->i_nlink == 0)
                 error =  -ENOENT;
+        else if (max_links && inode->i_nlink >= max_links)
+                error = -EMLINK;
         else
                 error = dir->i_op->link(old_dentry, dir, new_dentry);
         mutex_unlock(&inode->i_mutex);
@@ -3050,6 +3057,7 @@ static int vfs_rename_dir(struct inode *old_dir, struct dentry *old_dentry,
 {
         int error = 0;
         struct inode *target = new_dentry->d_inode;
+        unsigned max_links = new_dir->i_sb->s_max_links;
 
         /*
          * If we are going to change the parent - check write permissions,
@@ -3073,6 +3081,11 @@ static int vfs_rename_dir(struct inode *old_dir, struct dentry *old_dentry,
         if (d_mountpoint(old_dentry) || d_mountpoint(new_dentry))
                 goto out;
 
+        error = -EMLINK;
+        if (max_links && !target && new_dir != old_dir &&
+            new_dir->i_nlink >= max_links)
+                goto out;
+
         if (target)
                 shrink_dcache_parent(new_dentry);
         error = old_dir->i_op->rename(old_dir, old_dentry, new_dir, new_dentry);