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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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