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Message-ID: <87mxcw5d4x.fsf@linux.vnet.ibm.com>
Date: Thu, 20 Oct 2011 13:05:26 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To: "J. Bruce Fields" <bfields@...ldses.org>
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 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.
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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