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    SubjectRe: [RFC v6 02/40] vfs: Add MAY_CREATE_FILE and MAY_CREATE_DIR permission flags
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    On Tue, Aug 04, 2015 at 01:53:00PM +0200, Andreas Gruenbacher wrote:
    > 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.
    >
    > To allow checking for delete *and* create access when replacing an existing
    > file via vfs_rename(), add a replace parameter to may_delete().
    >
    > Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
    > ---
    > fs/namei.c | 42 ++++++++++++++++++++++++------------------
    > include/linux/fs.h | 2 ++
    > 2 files changed, 26 insertions(+), 18 deletions(-)
    >
    > diff --git a/fs/namei.c b/fs/namei.c
    > index 8f3db24..3504d36 100644
    > --- a/fs/namei.c
    > +++ b/fs/namei.c
    > @@ -453,7 +453,8 @@ 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.
    > + * When checking for MAY_APPEND, MAY_CREATE_FILE, MAY_CREATE_DIR,
    > + * MAY_WRITE must also be set in @mask.

    Why? (Also: written as a simple list like that, it's a ambiguous how to
    parse that comment: I think you mean that MAY_WRITE must be set whenever
    MAY_APPEND, MAY_CREATE_FILE, or MAY_CREATE_DIR are set.)

    --b.

    > */
    > int inode_permission(struct inode *inode, int mask)
    > {
    > @@ -2522,10 +2523,11 @@ 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(struct inode *dir, struct dentry *victim,
    > + bool isdir, bool replace)
    > {
    > struct inode *inode = d_backing_inode(victim);
    > - int error;
    > + int error, mask = MAY_WRITE | MAY_EXEC;
    >
    > if (d_is_negative(victim))
    > return -ENOENT;
    > @@ -2534,7 +2536,9 @@ 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);
    > + if (replace)
    > + mask |= isdir ? MAY_CREATE_DIR : MAY_CREATE_FILE;
    > + error = inode_permission(dir, mask);
    > if (error)
    > return error;
    > if (IS_APPEND(dir))
    > @@ -2565,14 +2569,16 @@ 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);
    > }
    >
    > /*
    > @@ -2622,7 +2628,7 @@ 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;
    >
    > @@ -3467,7 +3473,7 @@ 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;
    > @@ -3559,7 +3565,7 @@ 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)
    > @@ -3640,7 +3646,7 @@ 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, false);
    >
    > if (error)
    > return error;
    > @@ -3762,7 +3768,7 @@ 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, false);
    >
    > if (error)
    > return error;
    > @@ -3896,7 +3902,7 @@ 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;
    > @@ -3979,7 +3985,7 @@ 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;
    >
    > @@ -4167,19 +4173,19 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
    > if (source == target)
    > return 0;
    >
    > - error = may_delete(old_dir, old_dentry, is_dir);
    > + error = may_delete(old_dir, old_dentry, is_dir, false);
    > if (error)
    > 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_delete(new_dir, new_dentry, is_dir, true);
    > else
    > - error = may_delete(new_dir, new_dentry, new_is_dir);
    > + error = may_delete(new_dir, new_dentry, new_is_dir, true);
    > }
    > if (error)
    > return error;
    > @@ -4442,7 +4448,7 @@ 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 44e696e..9c44f27 100644
    > --- a/include/linux/fs.h
    > +++ b/include/linux/fs.h
    > @@ -81,6 +81,8 @@ 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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