2021-10-29 03:31:46

by Muchun Song

Subject: [PATCH] seq_file: fix passing wrong private data

DEFINE_PROC_SHOW_ATTRIBUTE() is supposed to be used to define a series
of functions and variables to register proc file easily. And the users
can use proc_create_data() to pass their own private data and get it
via seq->private in the callback. Unfortunately, the proc file system
use PDE_DATA() to get private data instead of inode->i_private. So fix
it. Fortunately, there only one user of it which does not pass any
private data, so this bug does not break any in-tree codes.

Fixes: 97a32539b956 ("proc: convert everything to "struct proc_ops"")
Signed-off-by: Muchun Song <[email protected]>
---
include/linux/seq_file.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
index 103776e18555..72dbb44a4573 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -209,7 +209,7 @@ static const struct file_operations __name ## _fops = { \
#define DEFINE_PROC_SHOW_ATTRIBUTE(__name) \
static int __name ## _open(struct inode *inode, struct file *file) \
{ \
- return single_open(file, __name ## _show, inode->i_private); \
+ return single_open(file, __name ## _show, PDE_DATA(inode)); \
} \
\
static const struct proc_ops __name ## _proc_ops = { \
--
2.11.0

2021-10-29 08:30:45

by Christian Brauner

Subject: Re: [PATCH] seq_file: fix passing wrong private data

On Fri, Oct 29, 2021 at 11:26:38AM +0800, Muchun Song wrote:
> DEFINE_PROC_SHOW_ATTRIBUTE() is supposed to be used to define a series
> of functions and variables to register proc file easily. And the users
> can use proc_create_data() to pass their own private data and get it
> via seq->private in the callback. Unfortunately, the proc file system
> use PDE_DATA() to get private data instead of inode->i_private. So fix
> it. Fortunately, there only one user of it which does not pass any
> private data, so this bug does not break any in-tree codes.
>
> Fixes: 97a32539b956 ("proc: convert everything to "struct proc_ops"")
> Signed-off-by: Muchun Song <[email protected]>
> ---
> include/linux/seq_file.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
> index 103776e18555..72dbb44a4573 100644
> --- a/include/linux/seq_file.h
> +++ b/include/linux/seq_file.h
> @@ -209,7 +209,7 @@ static const struct file_operations __name ## _fops = { \
> #define DEFINE_PROC_SHOW_ATTRIBUTE(__name) \
> static int __name ## _open(struct inode *inode, struct file *file) \
> { \
> - return single_open(file, __name ## _show, inode->i_private); \
> + return single_open(file, __name ## _show, PDE_DATA(inode)); \
> } \
> \
> static const struct proc_ops __name ## _proc_ops = { \

Hm, after your change DEFINE_SHOW_ATTRIBUTE() and
DEFINE_PROC_SHOW_ATTRIBUTE() macros do exactly the same things, right?:

#define DEFINE_SHOW_ATTRIBUTE(__name) \
static int __name ## _open(struct inode *inode, struct file *file) \
{ \
return single_open(file, __name ## _show, inode->i_private); \
} \
\
static const struct file_operations __name ## _fops = { \
.owner = THIS_MODULE, \
.open = __name ## _open, \
.read = seq_read, \
.llseek = seq_lseek, \
.release = single_release, \
}

#define DEFINE_PROC_SHOW_ATTRIBUTE(__name) \
static int __name ## _open(struct inode *inode, struct file *file) \
{ \
return single_open(file, __name ## _show, inode->i_private); \
} \

Can't you just replace the single instance where
DEFINE_PROC_SHOW_ATTRIBUTE with DEFINE_SHOW_ATTRIBUTE() and remove
DEFINE_PROC_SHOW_ATTRIBUTE completely?

Christian

2021-10-29 08:47:09

by Muchun Song

Subject: Re: [PATCH] seq_file: fix passing wrong private data

On Fri, Oct 29, 2021 at 4:26 PM Christian Brauner
<[email protected]> wrote:
>
> On Fri, Oct 29, 2021 at 11:26:38AM +0800, Muchun Song wrote:
> > DEFINE_PROC_SHOW_ATTRIBUTE() is supposed to be used to define a series
> > of functions and variables to register proc file easily. And the users
> > can use proc_create_data() to pass their own private data and get it
> > via seq->private in the callback. Unfortunately, the proc file system
> > use PDE_DATA() to get private data instead of inode->i_private. So fix
> > it. Fortunately, there only one user of it which does not pass any
> > private data, so this bug does not break any in-tree codes.
> >
> > Fixes: 97a32539b956 ("proc: convert everything to "struct proc_ops"")
> > Signed-off-by: Muchun Song <[email protected]>
> > ---
> > include/linux/seq_file.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
> > index 103776e18555..72dbb44a4573 100644
> > --- a/include/linux/seq_file.h
> > +++ b/include/linux/seq_file.h
> > @@ -209,7 +209,7 @@ static const struct file_operations __name ## _fops = { \
> > #define DEFINE_PROC_SHOW_ATTRIBUTE(__name) \
> > static int __name ## _open(struct inode *inode, struct file *file) \
> > { \
> > - return single_open(file, __name ## _show, inode->i_private); \
> > + return single_open(file, __name ## _show, PDE_DATA(inode)); \
> > } \
> > \
> > static const struct proc_ops __name ## _proc_ops = { \
>
> Hm, after your change DEFINE_SHOW_ATTRIBUTE() and
> DEFINE_PROC_SHOW_ATTRIBUTE() macros do exactly the same things, right?:

Unfortunately, they are not the same. The difference is the
operation structure, namely "struct file_operations" and
"struct proc_ops".

DEFINE_SHOW_ATTRIBUTE() is usually used by
debugfs while DEFINE_SHOW_ATTRIBUTE() is
used by procfs.

Thanks.

>
> #define DEFINE_SHOW_ATTRIBUTE(__name) \
> static int __name ## _open(struct inode *inode, struct file *file) \
> { \
> return single_open(file, __name ## _show, inode->i_private); \
> } \
> \
> static const struct file_operations __name ## _fops = { \
> .owner = THIS_MODULE, \
> .open = __name ## _open, \
> .read = seq_read, \
> .llseek = seq_lseek, \
> .release = single_release, \
> }
>
> #define DEFINE_PROC_SHOW_ATTRIBUTE(__name) \
> static int __name ## _open(struct inode *inode, struct file *file) \
> { \
> return single_open(file, __name ## _show, inode->i_private); \
> } \
>
> Can't you just replace the single instance where
> DEFINE_PROC_SHOW_ATTRIBUTE with DEFINE_SHOW_ATTRIBUTE() and remove
> DEFINE_PROC_SHOW_ATTRIBUTE completely?
>
> Christian

2021-10-29 08:52:42

by Christian Brauner

Subject: Re: [PATCH] seq_file: fix passing wrong private data

On Fri, Oct 29, 2021 at 04:43:40PM +0800, Muchun Song wrote:
> On Fri, Oct 29, 2021 at 4:26 PM Christian Brauner
> <[email protected]> wrote:
> >
> > On Fri, Oct 29, 2021 at 11:26:38AM +0800, Muchun Song wrote:
> > > DEFINE_PROC_SHOW_ATTRIBUTE() is supposed to be used to define a series
> > > of functions and variables to register proc file easily. And the users
> > > can use proc_create_data() to pass their own private data and get it
> > > via seq->private in the callback. Unfortunately, the proc file system
> > > use PDE_DATA() to get private data instead of inode->i_private. So fix
> > > it. Fortunately, there only one user of it which does not pass any
> > > private data, so this bug does not break any in-tree codes.
> > >
> > > Fixes: 97a32539b956 ("proc: convert everything to "struct proc_ops"")
> > > Signed-off-by: Muchun Song <[email protected]>
> > > ---
> > > include/linux/seq_file.h | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
> > > index 103776e18555..72dbb44a4573 100644
> > > --- a/include/linux/seq_file.h
> > > +++ b/include/linux/seq_file.h
> > > @@ -209,7 +209,7 @@ static const struct file_operations __name ## _fops = { \
> > > #define DEFINE_PROC_SHOW_ATTRIBUTE(__name) \
> > > static int __name ## _open(struct inode *inode, struct file *file) \
> > > { \
> > > - return single_open(file, __name ## _show, inode->i_private); \
> > > + return single_open(file, __name ## _show, PDE_DATA(inode)); \
> > > } \
> > > \
> > > static const struct proc_ops __name ## _proc_ops = { \
> >
> > Hm, after your change DEFINE_SHOW_ATTRIBUTE() and
> > DEFINE_PROC_SHOW_ATTRIBUTE() macros do exactly the same things, right?:
>
> Unfortunately, they are not the same. The difference is the
> operation structure, namely "struct file_operations" and
> "struct proc_ops".
>
> DEFINE_SHOW_ATTRIBUTE() is usually used by
> debugfs while DEFINE_SHOW_ATTRIBUTE() is
> used by procfs.

Ugh, right, thanks for pointing that out. I overlooked the _proc_ops
appendix. Not sure what's right here. There seem to have been earlier
callers to DEFINE_PROC_SHOW_ATTRIBUTE() that relied on PDE_DATA() but
there's only one caller so that change wouldn't be too bad, I guess.

2021-10-29 09:20:10

by Muchun Song

Subject: Re: [PATCH] seq_file: fix passing wrong private data

On Fri, Oct 29, 2021 at 4:50 PM Christian Brauner
<[email protected]> wrote:
>
> On Fri, Oct 29, 2021 at 04:43:40PM +0800, Muchun Song wrote:
> > On Fri, Oct 29, 2021 at 4:26 PM Christian Brauner
> > <[email protected]> wrote:
> > >
> > > On Fri, Oct 29, 2021 at 11:26:38AM +0800, Muchun Song wrote:
> > > > DEFINE_PROC_SHOW_ATTRIBUTE() is supposed to be used to define a series
> > > > of functions and variables to register proc file easily. And the users
> > > > can use proc_create_data() to pass their own private data and get it
> > > > via seq->private in the callback. Unfortunately, the proc file system
> > > > use PDE_DATA() to get private data instead of inode->i_private. So fix
> > > > it. Fortunately, there only one user of it which does not pass any
> > > > private data, so this bug does not break any in-tree codes.
> > > >
> > > > Fixes: 97a32539b956 ("proc: convert everything to "struct proc_ops"")
> > > > Signed-off-by: Muchun Song <[email protected]>
> > > > ---
> > > > include/linux/seq_file.h | 2 +-
> > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
> > > > index 103776e18555..72dbb44a4573 100644
> > > > --- a/include/linux/seq_file.h
> > > > +++ b/include/linux/seq_file.h
> > > > @@ -209,7 +209,7 @@ static const struct file_operations __name ## _fops = { \
> > > > #define DEFINE_PROC_SHOW_ATTRIBUTE(__name) \
> > > > static int __name ## _open(struct inode *inode, struct file *file) \
> > > > { \
> > > > - return single_open(file, __name ## _show, inode->i_private); \
> > > > + return single_open(file, __name ## _show, PDE_DATA(inode)); \
> > > > } \
> > > > \
> > > > static const struct proc_ops __name ## _proc_ops = { \
> > >
> > > Hm, after your change DEFINE_SHOW_ATTRIBUTE() and
> > > DEFINE_PROC_SHOW_ATTRIBUTE() macros do exactly the same things, right?:
> >
> > Unfortunately, they are not the same. The difference is the
> > operation structure, namely "struct file_operations" and
> > "struct proc_ops".
> >
> > DEFINE_SHOW_ATTRIBUTE() is usually used by
> > debugfs while DEFINE_SHOW_ATTRIBUTE() is
> > used by procfs.
>
> Ugh, right, thanks for pointing that out. I overlooked the _proc_ops
> appendix. Not sure what's right here. There seem to have been earlier
> callers to DEFINE_PROC_SHOW_ATTRIBUTE() that relied on PDE_DATA() but
> there's only one caller so that change wouldn't be too bad, I guess.

From my point of view, I think the macro is useful which can
simplify the code. However there is only one user of it. I suppose
few people know about it. For instance, the following ops can
become the user of it.

cifs_mount_params_proc_ops
nfsd_proc_ops
rpc_proc_ops

Thanks.