Re: [PATCH v14 02/22] vfs: Add MAY_CREATE_FILE and MAY_CREATE_DIR permission flags

Andreas Dilger
2015-11-08T08:18:55Z

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On Nov 7, 2015, at 10:44 AM, Andreas Gruenbacher <agruenba-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
>
> On Fri, Nov 6, 2015 at 9:58 PM, Andreas Dilger <adilger-m1MBpc4rdrD3fQ9qLvQP4Q@public.gmane.org> 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?

This is definitely better than the previous patch. You can add:

Reviewed-by: Andreas Dilger <adilger-m1MBpc4rdrD3fQ9qLvQP4Q@public.gmane.org>

Cheers, 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 <agruenba-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> Reviewed-by: J. Bruce Fields <bfields-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
> 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
>

Cheers, Andreas

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