[PATCH 01/23] rearrange may_open() to be r/o friendly

Dave Hansen
2007-07-12T00:18:33Z

may_open() calls vfs_permission() before it does checks for
IS_RDONLY(inode). It checks _again_ inside of vfs_permission().

The check inside of vfs_permission() is going away eventually.
With the mnt_want/drop_write() functions, all of the r/o
checks (except for this one) are consistently done before
calling permission(). Because of this, I'd like to use
permission() to hold a debugging check to make sure that
the mnt_want/drop_write() calls are actually being made.

So, to do this:
1. remove the IS_RDONLY() check from permission()
2. enforce that you must mnt_want_write() before
even calling permission()
3. enable a debugging in permission()

We need to rearrange may_open(). Here's the patch.

---

lxc-dave/fs/namei.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)

diff -puN fs/namei.c~rearrange-permission-and-ro-checks-in-may_open fs/namei.c
--- lxc/fs/namei.c~rearrange-permission-and-ro-checks-in-may_open 2007-07-10 12:46:01.000000000 -0700
+++ lxc-dave/fs/namei.c 2007-07-10 12:46:01.000000000 -0700
@@ -228,6 +228,10 @@ int permission(struct inode *inode, int
{
umode_t mode = inode->i_mode;
int retval, submask;
+ struct vfsmount *mnt = NULL;
+
+ if (nd)
+ mnt = nd->mnt;

if (mask & MAY_WRITE) {

@@ -252,7 +256,7 @@ int permission(struct inode *inode, int
* the fs is mounted with the "noexec" flag.
*/
if ((mask & MAY_EXEC) && S_ISREG(mode) && (!(mode & S_IXUGO) ||
- (nd && nd->mnt && (nd->mnt->mnt_flags & MNT_NOEXEC))))
+ (mnt && (mnt->mnt_flags & MNT_NOEXEC))))
return -EACCES;

/* Ordinary permission routines do not understand MAY_APPEND. */
@@ -1546,10 +1550,6 @@ int may_open(struct nameidata *nd, int a
if (S_ISDIR(inode->i_mode) && (flag & FMODE_WRITE))
return -EISDIR;

- error = vfs_permission(nd, acc_mode);
- if (error)
- return error;
-
/*
* FIFO's, sockets and device files are special: they don't
* actually live on the filesystem itself, and as such you
@@ -1564,6 +1564,10 @@ int may_open(struct nameidata *nd, int a
flag &= ~O_TRUNC;
} else if (IS_RDONLY(inode) && (flag & FMODE_WRITE))
return -EROFS;
+
+ error = vfs_permission(nd, acc_mode);
+ if (error)
+ return error;
/*
* An append-only file must be opened in append mode for writing.
*/
_