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Subject[PATCH 09/10] VFS: Remove read-only checks from dentry_permission
It is not sufficient to depend on the the "filesystem is readonly"
tests in dentry_permission as it does not check if the vfsmnt is
readonly.
All call sites already call mnt_want_write or __mnt_is_readonly which
includes the test on MS_RDONLY.

So remove this test from dentry_permission as it simply duplicates
tests done elsewhere.

This allows ovl_permission to be significantly simplified.


Cc: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: NeilBrown <neilb@suse.de>
---
fs/namei.c | 15 +--------------
fs/overlayfs/overlayfs.c | 26 ++------------------------
2 files changed, 3 insertions(+), 38 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index 6042564..291a839 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -254,22 +254,9 @@ int dentry_permission(struct dentry *dentry, int mask)
struct inode *inode = dentry->d_inode;
int retval;

- if (mask & MAY_WRITE) {
- umode_t mode = inode->i_mode;
-
- /*
- * Nobody gets write access to a read-only fs.
- */
- if (IS_RDONLY(inode) &&
- (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
- return -EROFS;
-
- /*
- * Nobody gets write access to an immutable file.
- */
+ if (mask & MAY_WRITE)
if (IS_IMMUTABLE(inode))
return -EACCES;
- }

if (inode->i_op->permission)
retval = inode->i_op->permission(dentry, mask);
diff --git a/fs/overlayfs/overlayfs.c b/fs/overlayfs/overlayfs.c
index cdeafa7..749109a 100644
--- a/fs/overlayfs/overlayfs.c
+++ b/fs/overlayfs/overlayfs.c
@@ -1127,31 +1127,9 @@ static int ovl_dir_getattr(struct vfsmount *mnt, struct dentry *dentry,
static int ovl_permission(struct dentry *dentry, int mask)
{
struct ovl_entry *ue = dentry->d_fsdata;
- struct inode *inode;
- int err;
-
- if (ue->upperpath.dentry)
- return dentry_permission(ue->upperpath.dentry, mask);
-
- inode = ue->lowerpath.dentry->d_inode;
- if (!(mask & MAY_WRITE) || special_file(inode->i_mode))
- return dentry_permission(ue->lowerpath.dentry, mask);
-
- /* Don't check for read-only fs */
- if (mask & MAY_WRITE) {
- if (IS_IMMUTABLE(inode))
- return -EACCES;
- }
-
- if (inode->i_op->permission)
- err = inode->i_op->permission(ue->lowerpath.dentry, mask);
- else
- err = generic_permission(inode, mask, inode->i_op->check_acl);
-
- if (err)
- return err;
+ struct path *realpath = ovl_path(ue);

- return security_inode_permission(inode, mask);
+ return dentry_permission(realpath->dentry, mask);
}

static int ovl_create_object(struct dentry *dentry, int mode, dev_t rdev,



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