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SubjectRe: [PATCH -V6 09/26] vfs: Add delete child and delete self permission flags
On Mon, Sep 05, 2011 at 10:55:31PM +0530, Aneesh Kumar K.V wrote:
> From: Andreas Gruenbacher <agruen@kernel.org>
>
> 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@kernel.org>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> ---
> fs/namei.c | 41 +++++++++++++++++++++++++++--------------
> include/linux/fs.h | 2 ++
> 2 files changed, 29 insertions(+), 14 deletions(-)
>
> diff --git a/fs/namei.c b/fs/namei.c
> index d52a4cd..eacb530 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -337,7 +337,7 @@ static inline int do_inode_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)
> {
> @@ -1862,7 +1862,7 @@ static inline int check_sticky(struct inode *dir, struct inode *inode)
> return 0;
>
> other_userns:
> - return !ns_capable(inode_userns(inode), CAP_FOWNER);
> + return 1;
> }
>
> /*
> @@ -1884,30 +1884,43 @@ other_userns:
> * 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)
> {
> - int error;
> + int mask, error, is_sticky;
> + struct inode *inode = victim->d_inode;
>
> - 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;

I'm having trouble understanding this next bit:

> + is_sticky = check_sticky(dir, inode);
> + error = inode_permission(dir, mask);
> + if ((error || is_sticky) && IS_RICHACL(inode) &&
> + !inode_permission(dir, mask & ~(MAY_WRITE | MAY_DELETE_CHILD)) &&
> + !inode_permission(inode, MAY_DELETE_SELF))
> + error = 0;

OK, so we can ignore the lack of write or delete permissions on the
parent if we have delete_self permissions on the child. I guess that's
right.

Why the "|| is_sticky" above?
Is there some less complicated why to write this?

--b.

> + else if (!error && is_sticky &&
> + !ns_capable(inode_userns(inode), CAP_FOWNER))
> + 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;
> @@ -2614,7 +2627,7 @@ 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;
> @@ -2707,7 +2720,7 @@ 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;
> @@ -3101,14 +3114,14 @@ 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 8707f43..c5c98c5 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -69,6 +69,8 @@ struct inodes_stat_t {
> #define MAY_NOT_BLOCK 0x00000080
> #define MAY_CREATE_FILE 0x00000100
> #define MAY_CREATE_DIR 0x00000200
> +#define MAY_DELETE_CHILD 0x00000400
> +#define MAY_DELETE_SELF 0x00000800
>
> /*
> * flags in file.f_mode. Note that FMODE_READ and FMODE_WRITE must correspond
> --
> 1.7.4.1
>


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