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Date: Thu, 20 Oct 2011 04:11:47 -0400
From: "J. Bruce Fields" <bfields@...ldses.org>
To: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc: agruen@...nel.org, akpm@...ux-foundation.org,
viro@...iv.linux.org.uk, dhowells@...hat.com,
linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V7 09/26] vfs: Add delete child and delete self
permission flags
On Thu, Oct 20, 2011 at 01:05:26PM +0530, Aneesh Kumar K.V wrote:
> On Wed, 19 Oct 2011 18:09:15 -0400, "J. Bruce Fields" <bfields@...ldses.org> wrote:
> > Maybe I'm dense, but that big if-else-if is still giving me a headache.
> >
> > The point is just to delay the ns_capable() check to avoid setting
> > PF_SUPERPRIV in cases where we weren't before?
> >
> > How about putting using a helper function for the richacl check, and
> > calling it from check_sticky instead? That makes the above:
> >
> > error = inode_permission(dir, mask | replace_mask);
> > if (error && !richacl_may_delete(dir, inode, replace_mask))
> > return error;
> > if (check_sticky(dir, inode, replace_mask))
> > return -EPERM;
> >
> > (As in the following--totally untested and possibly wrong.)
> >
> > Also: the comment before may_delete() needs updating.
> >
>
> Thanks for the suggestion. That made the code simpler. Updated patch
> below.
Looks good to me if it passes your tests, thanks! Feel free to add
Reviewed-by or Acked-by for "J. Bruce Fields" <bfields@...hat.com>.
--b.
>
> commit 3c92363ce2dee22aa174327c21726f8f02cbcd6e
> Author: Andreas Gruenbacher <agruen@...nel.org>
> Date: Tue Oct 18 15:17:50 2011 +0530
>
> vfs: Add delete child and delete self permission flags
>
> 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()
>
> Acked-by: David Howells <dhowells@...hat.com>
> Signed-off-by: Andreas Gruenbacher <agruen@...nel.org>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
>
> diff --git a/fs/namei.c b/fs/namei.c
> index f6184b8..044b6d1 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)
> {
> @@ -1835,11 +1835,25 @@ static int user_path_parent(int dfd, const char __user *path,
> return error;
> }
>
> +
> +/*
> + * We should have exec permission on directory and MAY_DELETE_SELF
> + * on the object being deleted.
> + */
> +static int richacl_may_selfdelete(struct inode *dir,
> + struct inode *inode, int replace_mask)
> +{
> + return (IS_RICHACL(inode) &&
> + (inode_permission(dir, MAY_EXEC | replace_mask) == 0) &&
> + (inode_permission(inode, MAY_DELETE_SELF) == 0));
> +}
> +
> /*
> * It's inline, so penalty for filesystems that don't use sticky bit is
> * minimal.
> */
> -static inline int check_sticky(struct inode *dir, struct inode *inode)
> +static inline int check_sticky(struct inode *dir,
> + struct inode *inode, int replace_mask)
> {
> uid_t fsuid = current_fsuid();
>
> @@ -1851,7 +1865,8 @@ static inline int check_sticky(struct inode *dir, struct inode *inode)
> return 0;
> if (dir->i_uid == fsuid)
> return 0;
> -
> + if (richacl_may_selfdelete(dir, inode, replace_mask))
> + return 0;
> other_userns:
> return !ns_capable(inode_userns(inode), CAP_FOWNER);
> }
> @@ -1875,30 +1890,38 @@ 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, replace_mask = 0, error;
> + 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)
> + replace_mask = S_ISDIR(inode->i_mode) ?
> + MAY_CREATE_DIR : MAY_CREATE_FILE;
> + error = inode_permission(dir, mask | replace_mask);
> + if (error && richacl_may_selfdelete(dir, inode, replace_mask))
> + error = 0;
> 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 (check_sticky(dir, inode, replace_mask) || 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;
> @@ -2605,7 +2628,7 @@ 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;
> @@ -2700,7 +2723,7 @@ 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;
> @@ -3096,14 +3119,14 @@ 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 60361c6..ccece40 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
>
--
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