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Message-Id: <1446918268-858-1-git-send-email-agruenba@redhat.com>
Date: Sat, 7 Nov 2015 18:44:28 +0100
From: Andreas Gruenbacher <agruenba@...hat.com>
To: Andreas Dilger <adilger@...ger.ca>
Cc: Andreas Gruenbacher <agruenba@...hat.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
"Theodore Ts'o" <tytso@....edu>,
"J. Bruce Fields" <bfields@...ldses.org>,
Jeff Layton <jlayton@...chiereds.net>,
Trond Myklebust <trond.myklebust@...marydata.com>,
Anna Schumaker <anna.schumaker@...app.com>,
Dave Chinner <david@...morbit.com>, linux-ext4@...r.kernel.org,
xfs@....sgi.com, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
linux-cifs@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [PATCH v14 02/22] vfs: Add MAY_CREATE_FILE and MAY_CREATE_DIR permission flags
On Fri, Nov 6, 2015 at 9:58 PM, Andreas Dilger <adilger@...ger.ca> 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?
Thanks,
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@...hat.com>
Reviewed-by: J. Bruce Fields <bfields@...hat.com>
---
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
--
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