[PATCH -V4 09/11] vfs: Add delete child and delete self permission flags

[Aneesh Kumar K.V]

From: Andreas Gruenbacher <agruen@xxxxxxx>

Normally, deleting a file requires write access to the parent directory.
Some permission models use a different permission on the parent
directory to indicate delete access.  In addition, a process can have
per-file delete access even without delete access on the parent
directory.

Introduce two new inode_permission() mask flags and use them in
may_delete()

Signed-off-by: Andreas Gruenbacher <agruen@xxxxxxx>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
---
 fs/namei.c         |   36 ++++++++++++++++++++++++------------
 include/linux/fs.h |    2 ++
 2 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index ed786b2..24c1e8c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -254,7 +254,7 @@ int generic_permission(struct inode *inode, int mask,
  * are used for other things.
  *
  * When checking for MAY_APPEND, MAY_CREATE_FILE, MAY_CREATE_DIR,
- * MAY_WRITE must also be set in @mask.
+ * MAY_DELETE_CHILD, MAY_DELETE_SELF, MAY_WRITE must also be set in @mask.
  */
 int inode_permission(struct inode *inode, int mask)
 {
@@ -1298,30 +1298,42 @@ static inline int check_sticky(struct inode *dir, struct inode *inode)
  * 10. We don't allow removal of NFS sillyrenamed files; it's handled by
  *     nfs_async_unlink().
  */
-static int may_delete(struct inode *dir,struct dentry *victim,int isdir)
+static int may_delete(struct inode *dir, struct dentry *victim,
+		      int isdir, int replace)
 {
+	struct inode *inode = victim->d_inode;
+	int mask;
 	int error;
 
-	if (!victim->d_inode)
+	if (!inode)
 		return -ENOENT;
 
 	BUG_ON(victim->d_parent->d_inode != dir);
 	audit_inode_child(victim, dir);
 
-	error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
+	mask = MAY_WRITE | MAY_EXEC | MAY_DELETE_CHILD;
+	if (replace)
+		mask |= S_ISDIR(inode->i_mode) ?
+			MAY_CREATE_DIR : MAY_CREATE_FILE;
+	error = inode_permission(dir, mask);
+	if (error && IS_RICHACL(inode) &&
+	    !inode_permission(dir, MAY_EXEC) &&
+	    !inode_permission(inode, MAY_WRITE | MAY_DELETE_SELF))
+		error = 0;
+	else if (!error && check_sticky(dir, inode))
+		error = -EPERM;
 	if (error)
 		return error;
 	if (IS_APPEND(dir))
 		return -EPERM;
-	if (check_sticky(dir, victim->d_inode)||IS_APPEND(victim->d_inode)||
-	    IS_IMMUTABLE(victim->d_inode) || IS_SWAPFILE(victim->d_inode))
+	if (IS_APPEND(inode) || IS_IMMUTABLE(inode) || IS_SWAPFILE(inode))
 		return -EPERM;
 	if (isdir) {
-		if (!S_ISDIR(victim->d_inode->i_mode))
+		if (!S_ISDIR(inode->i_mode))
 			return -ENOTDIR;
 		if (IS_ROOT(victim))
 			return -EBUSY;
-	} else if (S_ISDIR(victim->d_inode->i_mode))
+	} else if (S_ISDIR(inode->i_mode))
 		return -EISDIR;
 	if (IS_DEADDIR(dir))
 		return -ENOENT;
@@ -2150,7 +2162,7 @@ void dentry_unhash(struct dentry *dentry)
 
 int vfs_rmdir(struct inode *dir, struct dentry *dentry)
 {
-	int error = may_delete(dir, dentry, 1);
+	int error = may_delete(dir, dentry, 1, 0);
 
 	if (error)
 		return error;
@@ -2237,7 +2249,7 @@ SYSCALL_DEFINE1(rmdir, const char __user *, pathname)
 
 int vfs_unlink(struct inode *dir, struct dentry *dentry)
 {
-	int error = may_delete(dir, dentry, 0);
+	int error = may_delete(dir, dentry, 0, 0);
 
 	if (error)
 		return error;
@@ -2629,14 +2641,14 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 	if (old_dentry->d_inode == new_dentry->d_inode)
  		return 0;
  
-	error = may_delete(old_dir, old_dentry, is_dir);
+	error = may_delete(old_dir, old_dentry, is_dir, 0);
 	if (error)
 		return error;
 
 	if (!new_dentry->d_inode)
 		error = may_create(new_dir, new_dentry, is_dir);
 	else
-		error = may_delete(new_dir, new_dentry, is_dir);
+		error = may_delete(new_dir, new_dentry, is_dir, 1);
 	if (error)
 		return error;
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 5dc1ebd..845a930 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -57,6 +57,8 @@ struct inodes_stat_t {
 #define MAY_CHDIR 64
 #define MAY_CREATE_FILE 128
 #define MAY_CREATE_DIR 256
+#define MAY_DELETE_CHILD 512
+#define MAY_DELETE_SELF 1024
 
 /*
  * flags in file.f_mode.  Note that FMODE_READ and FMODE_WRITE must correspond
-- 
1.7.0.4

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