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Date: Wed, 2 Sep 2015 14:53:00 -0400
From: bfields@...ldses.org (J. Bruce Fields)
To: Andreas Gruenbacher <andreas.gruenbacher@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-nfs@...r.kernel.org, linux-api@...r.kernel.org,
linux-cifs@...r.kernel.org, linux-security-module@...r.kernel.org,
Andreas Gruenbacher <agruenba@...hat.com>
Subject: Re: [RFC v6 02/40] vfs: Add MAY_CREATE_FILE and MAY_CREATE_DIR
permission flags
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@...hat.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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