On Fri, Nov 6, 2015 at 9:58 PM, Andreas Dilger <adil...@dilger.ca> wrote:
> I thought you proposed adding an enum for these parameters, and possibly
> making them a single parameter flag, to make the code in the caller more
> readable.

No, the result would just be different but not any better; vfs_rename would
become messy.  I've played with this patch some more, and I find the approach
below which splits may_delete into may_delete and may_replace much better.
What do you think?

Thanks,
Andreas

---------- 8< ----------

Richacls distinguish between creating non-directories and directories. To
support that, add an isdir parameter to may_create(). When checking
inode_permission() for create permission, pass in an additional
MAY_CREATE_FILE or MAY_CREATE_DIR mask flag.

Add may_replace() to allow checking for delete and create access when
replacing an existing file in vfs_rename().

Signed-off-by: Andreas Gruenbacher <agrue...@redhat.com>
Reviewed-by: J. Bruce Fields <bfie...@redhat.com>
---
 fs/namei.c         | 49 +++++++++++++++++++++++++++++++++----------------
 include/linux/fs.h |  2 ++
 2 files changed, 35 insertions(+), 16 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 224ecf1..4e5dc2f 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -453,7 +453,9 @@ static int sb_permission(struct super_block *sb, struct 
inode *inode, int mask)
  * this, letting us set arbitrary permissions for filesystem access without
  * changing the "normal" UIDs which are used for other things.
  *
- * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask.
+ * MAY_WRITE must be set in @mask whenever MAY_APPEND, MAY_CREATE_FILE, or
+ * MAY_CREATE_DIR are set.  That way, file systems that don't support these
+ * permissions will check for MAY_WRITE instead.
  */
 int inode_permission(struct inode *inode, int mask)
 {
@@ -2549,7 +2551,8 @@ EXPORT_SYMBOL(__check_sticky);
  * 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, bool isdir)
+static int may_delete_replace(struct inode *dir, struct dentry *victim,
+                             bool isdir, int mask)
 {
        struct inode *inode = d_backing_inode(victim);
        int error;
@@ -2561,7 +2564,7 @@ static int may_delete(struct inode *dir, struct dentry 
*victim, bool isdir)
        BUG_ON(victim->d_parent->d_inode != dir);
        audit_inode_child(dir, victim, AUDIT_TYPE_CHILD_DELETE);
 
-       error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
+       error = inode_permission(dir, mask | MAY_WRITE | MAY_EXEC);
        if (error)
                return error;
        if (IS_APPEND(dir))
@@ -2584,6 +2587,18 @@ static int may_delete(struct inode *dir, struct dentry 
*victim, bool isdir)
        return 0;
 }
 
+static int may_delete(struct inode *dir, struct dentry *victim, bool isdir)
+{
+       return may_delete_replace(dir, victim, isdir, 0);
+}
+
+static int may_replace(struct inode *dir, struct dentry *victim, bool isdir)
+{
+       int mask = isdir ? MAY_CREATE_DIR : MAY_CREATE_FILE;
+
+       return may_delete_replace(dir, victim, isdir, mask);
+}
+
 /*     Check whether we can create an object with dentry child in directory
  *  dir.
  *  1. We can't do it if child already exists (open has special treatment for
@@ -2592,14 +2607,16 @@ static int may_delete(struct inode *dir, struct dentry 
*victim, bool isdir)
  *  3. We should have write and exec permissions on dir
  *  4. We can't do it if dir is immutable (done in permission())
  */
-static inline int may_create(struct inode *dir, struct dentry *child)
+static inline int may_create(struct inode *dir, struct dentry *child, bool 
isdir)
 {
+       int mask = isdir ? MAY_CREATE_DIR : MAY_CREATE_FILE;
+
        audit_inode_child(dir, child, AUDIT_TYPE_CHILD_CREATE);
        if (child->d_inode)
                return -EEXIST;
        if (IS_DEADDIR(dir))
                return -ENOENT;
-       return inode_permission(dir, MAY_WRITE | MAY_EXEC);
+       return inode_permission(dir, MAY_WRITE | MAY_EXEC | mask);
 }
 
 /*
@@ -2649,7 +2666,7 @@ EXPORT_SYMBOL(unlock_rename);
 int vfs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
                bool want_excl)
 {
-       int error = may_create(dir, dentry);
+       int error = may_create(dir, dentry, false);
        if (error)
                return error;
 
@@ -3494,7 +3511,7 @@ EXPORT_SYMBOL(user_path_create);
 
 int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t 
dev)
 {
-       int error = may_create(dir, dentry);
+       int error = may_create(dir, dentry, false);
 
        if (error)
                return error;
@@ -3586,7 +3603,7 @@ 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);
+       int error = may_create(dir, dentry, true);
        unsigned max_links = dir->i_sb->s_max_links;
 
        if (error)
@@ -3667,7 +3684,7 @@ EXPORT_SYMBOL(dentry_unhash);
 
 int vfs_rmdir(struct inode *dir, struct dentry *dentry)
 {
-       int error = may_delete(dir, dentry, 1);
+       int error = may_delete(dir, dentry, true);
 
        if (error)
                return error;
@@ -3789,7 +3806,7 @@ SYSCALL_DEFINE1(rmdir, const char __user *, pathname)
 int vfs_unlink(struct inode *dir, struct dentry *dentry, struct inode 
**delegated_inode)
 {
        struct inode *target = dentry->d_inode;
-       int error = may_delete(dir, dentry, 0);
+       int error = may_delete(dir, dentry, false);
 
        if (error)
                return error;
@@ -3923,7 +3940,7 @@ SYSCALL_DEFINE1(unlink, const char __user *, pathname)
 
 int vfs_symlink(struct inode *dir, struct dentry *dentry, const char *oldname)
 {
-       int error = may_create(dir, dentry);
+       int error = may_create(dir, dentry, false);
 
        if (error)
                return error;
@@ -4006,7 +4023,7 @@ int vfs_link(struct dentry *old_dentry, struct inode 
*dir, struct dentry *new_de
        if (!inode)
                return -ENOENT;
 
-       error = may_create(dir, new_dentry);
+       error = may_create(dir, new_dentry, false);
        if (error)
                return error;
 
@@ -4199,14 +4216,14 @@ int vfs_rename(struct inode *old_dir, struct dentry 
*old_dentry,
                return error;
 
        if (!target) {
-               error = may_create(new_dir, new_dentry);
+               error = may_create(new_dir, new_dentry, is_dir);
        } else {
                new_is_dir = d_is_dir(new_dentry);
 
                if (!(flags & RENAME_EXCHANGE))
-                       error = may_delete(new_dir, new_dentry, is_dir);
+                       error = may_replace(new_dir, new_dentry, is_dir);
                else
-                       error = may_delete(new_dir, new_dentry, new_is_dir);
+                       error = may_replace(new_dir, new_dentry, new_is_dir);
        }
        if (error)
                return error;
@@ -4469,7 +4486,7 @@ SYSCALL_DEFINE2(rename, const char __user *, oldname, 
const char __user *, newna
 
 int vfs_whiteout(struct inode *dir, struct dentry *dentry)
 {
-       int error = may_create(dir, dentry);
+       int error = may_create(dir, dentry, false);
        if (error)
                return error;
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 4efa435..d6e2330 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -82,6 +82,8 @@ typedef void (dax_iodone_t)(struct buffer_head *bh_map, int 
uptodate);
 #define MAY_CHDIR              0x00000040
 /* called from RCU mode, don't block */
 #define MAY_NOT_BLOCK          0x00000080
+#define MAY_CREATE_FILE                0x00000100
+#define MAY_CREATE_DIR         0x00000200
 
 /*
  * flags in file.f_mode.  Note that FMODE_READ and FMODE_WRITE must correspond
-- 
2.5.0

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