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SubjectRe: [PATCH -V7 09/26] vfs: Add delete child and delete self permission flags
On Tue, Oct 18, 2011 at 09:02:44PM +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()
>
> Acked-by: David Howells <dhowells@redhat.com>
> Signed-off-by: Andreas Gruenbacher <agruen@kernel.org>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> ---
> fs/namei.c | 42 ++++++++++++++++++++++++++++--------------
> include/linux/fs.h | 2 ++
> 2 files changed, 30 insertions(+), 14 deletions(-)
>
> diff --git a/fs/namei.c b/fs/namei.c
> index f6184b8..7bf42e8 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)
> {
> @@ -1853,7 +1853,7 @@ 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;
> }
>
> /*
> @@ -1875,30 +1875,44 @@ 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;
> + struct inode *inode = victim->d_inode;
> + int mask, replace_mask = 0, error, is_sticky;
> +
>
> - 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;
> + is_sticky = check_sticky(dir, inode);
> + error = inode_permission(dir, mask | replace_mask);
> + if ((error || is_sticky) && IS_RICHACL(inode) &&
> + (inode_permission(dir, MAY_EXEC | replace_mask) == 0) &&
> + (inode_permission(inode, MAY_DELETE_SELF) == 0))
> + error = 0;
> + else if (!error && is_sticky &&
> + !ns_capable(inode_userns(inode), CAP_FOWNER))
> + error = -EPERM;

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.

--b.

commit 7fe4b12ba6b914167ed1f1bc617af04eecbce7d1
Author: Andreas Gruenbacher <agruen@kernel.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@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruen@kernel.org>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

diff --git a/fs/namei.c b/fs/namei.c
index f6184b8..f0cccd9 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 +1835,18 @@ static int user_path_parent(int dfd, const char __user *path,
return error;
}

+static bool richacl_may_delete(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 +1858,8 @@ static inline int check_sticky(struct inode *dir, struct inode *inode)
return 0;
if (dir->i_uid == fsuid)
return 0;
-
+ if (richacl_may_delete(dir, inode, replace_mask))
+ return 0;
other_userns:
return !ns_capable(inode_userns(inode), CAP_FOWNER);
}
@@ -1875,30 +1883,38 @@ 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;
+ struct inode *inode = victim->d_inode;
+ int mask, replace_mask = 0, error;
+

- 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);
- if (error)
+ 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_delete(dir, inode, replace_mask))
return error;
+ if (check_sticky(dir, inode, replace_mask))
+ return -EPERM;
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;
@@ -2605,7 +2621,7 @@ 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 +2716,7 @@ 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 +3112,14 @@ 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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