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SubjectRe: [PATCH -V14 04/11] vfs: Allow handle based open on symlinks
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On Thu, 8 Jul 2010 02:48:59 +1000, Nick Piggin <npiggin@suse.de> wrote:
> On Tue, Jun 15, 2010 at 10:42:54PM +0530, Aneesh Kumar K.V wrote:
> > The patch update may_open to allow handle based open on symlinks.
> > The file handle based API use file descritor returned from open_by_handle_at
> > to do different file system operations. To find the link target name we
> > need to get a file descriptor on symlinks.
> >
> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> > ---
> > fs/namei.c | 17 ++++++++++++++---
> > 1 files changed, 14 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/namei.c b/fs/namei.c
> > index c2d19c7..417bf53 100644
> > --- a/fs/namei.c
> > +++ b/fs/namei.c
> > @@ -1422,7 +1422,7 @@ int vfs_create(struct inode *dir, struct dentry *dentry, int mode,
> > return error;
> > }
> >
> > -int may_open(struct path *path, int acc_mode, int flag)
> > +static int __may_open(struct path *path, int acc_mode, int flag, int handle)
> > {
> > struct dentry *dentry = path->dentry;
> > struct inode *inode = dentry->d_inode;
> > @@ -1433,7 +1433,13 @@ int may_open(struct path *path, int acc_mode, int flag)
> >
> > switch (inode->i_mode & S_IFMT) {
> > case S_IFLNK:
> > - return -ELOOP;
> > + /*
> > + * For file handle based open we should allow
> > + * open of symlink.
> > + */
> > + if (!handle)
> > + return -ELOOP;
> > + break;
> > case S_IFDIR:
> > if (acc_mode & MAY_WRITE)
> > return -EISDIR;
> > @@ -1473,6 +1479,11 @@ int may_open(struct path *path, int acc_mode, int flag)
> > return break_lease(inode, flag);
> > }
> >
> > +int may_open(struct path *path, int acc_mode, int flag)
> > +{
> > + return __may_open(path, acc_mode, flag, 0);
> > +}
>
> Why don't you just add MAY_OPEN_LNK instead of this ugliness?
>

Something like the below ?

commit 69787f5ed6c8a7a63ad21ef5d7de0b62f124ff0a
Author: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Date: Tue Jul 6 23:25:57 2010 +0530

vfs: Allow handle based open on symlinks

The patch update may_open to allow handle based open on symlinks.
The file handle based API use file descritor returned from open_by_handle_at
to do different file system operations. To find the link target name we
need to get a file descriptor on symlinks.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

diff --git a/fs/namei.c b/fs/namei.c
index de40312..2ea5c79 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1456,7 +1456,15 @@ int may_open(struct path *path, int acc_mode, int flag)

switch (inode->i_mode & S_IFMT) {
case S_IFLNK:
- return -ELOOP;
+ /*
+ * Allow only if acc_mode contain
+ * open link request and read request.
+ */
+ if (acc_mode != (MAY_OPEN_LINK | MAY_READ))
+ return -ELOOP;
+ if (flag != O_RDONLY)
+ return -ELOOP;
+ break;
case S_IFDIR:
if (acc_mode & MAY_WRITE)
return -EISDIR;
diff --git a/fs/open.c b/fs/open.c
index daf2534..a58837a 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1266,8 +1266,15 @@ static long do_sys_open_by_handle(int mountdirfd,
*/
if (open_flag & __O_SYNC)
open_flag |= O_DSYNC;
+ /*
+ * Handle based API allow open on a symlink
+ */
+ if (S_ISLNK(path->dentry->d_inode->i_mode))
+ acc_mode = MAY_OPEN_LINK;
+ else
+ acc_mode = MAY_OPEN;

- acc_mode = MAY_OPEN | ACC_MODE(open_flag);
+ acc_mode |= ACC_MODE(open_flag);

/* O_TRUNC implies we need access checks for write permissions */
if (open_flag & O_TRUNC)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index cbff4ca..eaf13d1 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -53,6 +53,7 @@ struct inodes_stat_t {
#define MAY_APPEND 8
#define MAY_ACCESS 16
#define MAY_OPEN 32
+#define MAY_OPEN_LINK 64

/*
* flags in file.f_mode. Note that FMODE_READ and FMODE_WRITE must correspond

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