Re: [PATCH 3/5] net: Set fput_needed iff FDPUT_FPUT is set

Re: [PATCH 3/5] net: Set fput_needed iff FDPUT_FPUT is set

[linmiaohe]

Al Viro <viro@zeniv.linux.org.uk> wrote:
>On Thu, Aug 06, 2020 at 12:59:16PM +0100, Al Viro wrote:
>> On Thu, Aug 06, 2020 at 07:53:16PM +0800, linmiaohe wrote:
>> > From: Miaohe Lin <linmiaohe@huawei.com>
>> > 
>> > We should fput() file iff FDPUT_FPUT is set. So we should set 
>> > fput_needed accordingly.
>> > 
>> > Fixes: 00e188ef6a7e ("sockfd_lookup_light(): switch to fdget^W^Waway 
>> > from fget_light")
>> 
>> Explain, please.  We are getting it from fdget(); what else can we get in flags there?
>
>FWIW, struct fd ->flags may have two bits set: FDPUT_FPUT and FDPUT_POS_UNLOCK.
>The latter is set only by __fdget_pos() and its callers, and that only for regular files and directories.
>
>Nevermind that sockfd_lookup_light() does *not* use ..._pos() family of primitives, even if it started to use e.g. fdget_pos() it *still* would not end up with anything other than FDPUT_FPUT to deal with on that path - it checks that what it got is a socket.  Anything else is dropped right there, without leaving fput() to caller.
>
>So could you explain what exactly the bug is - if you are seeing some breakage and this patch fixes it, something odd is definitely going on and it would be nice to figure out what that something is.

I'am sorry, but I did not find something odd. I do this because this would make code more clear and consistent. It's pure a clean up patch.
Maybe Fixes tag makes this looks like a bugfix.

Thanks for your reply and detailed explaination. :)

And sorry for my rookie mistake, I wasn't meant to make these as a patch set...

Re: [PATCH 3/5] net: Set fput_needed iff FDPUT_FPUT is set

[David Miller]

From: linmiaohe <linmiaohe@huawei.com>
Date: Thu, 6 Aug 2020 19:53:16 +0800

> From: Miaohe Lin <linmiaohe@huawei.com>
> 
> We should fput() file iff FDPUT_FPUT is set. So we should set fput_needed
> accordingly.
> 
> Fixes: 00e188ef6a7e ("sockfd_lookup_light(): switch to fdget^W^Waway from fget_light")
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>

Applied.

Re: [PATCH 3/5] net: Set fput_needed iff FDPUT_FPUT is set

[Al Viro]

On Thu, Aug 06, 2020 at 12:59:16PM +0100, Al Viro wrote:
> On Thu, Aug 06, 2020 at 07:53:16PM +0800, linmiaohe wrote:
> > From: Miaohe Lin <linmiaohe@huawei.com>
> > 
> > We should fput() file iff FDPUT_FPUT is set. So we should set fput_needed
> > accordingly.
> > 
> > Fixes: 00e188ef6a7e ("sockfd_lookup_light(): switch to fdget^W^Waway from fget_light")
> 
> Explain, please.  We are getting it from fdget(); what else can we get in flags there?

FWIW, struct fd ->flags may have two bits set: FDPUT_FPUT and FDPUT_POS_UNLOCK.
The latter is set only by __fdget_pos() and its callers, and that only for
regular files and directories.

Nevermind that sockfd_lookup_light() does *not* use ..._pos() family of
primitives, even if it started to use e.g. fdget_pos() it *still* would
not end up with anything other than FDPUT_FPUT to deal with on that
path - it checks that what it got is a socket.  Anything else is dropped
right there, without leaving fput() to caller.

So could you explain what exactly the bug is - if you are seeing some
breakage and this patch fixes it, something odd is definitely going on
and it would be nice to figure out what that something is.

Re: [PATCH 3/5] net: Set fput_needed iff FDPUT_FPUT is set

[Al Viro]

On Thu, Aug 06, 2020 at 07:53:16PM +0800, linmiaohe wrote:
> From: Miaohe Lin <linmiaohe@huawei.com>
> 
> We should fput() file iff FDPUT_FPUT is set. So we should set fput_needed
> accordingly.
> 
> Fixes: 00e188ef6a7e ("sockfd_lookup_light(): switch to fdget^W^Waway from fget_light")

Explain, please.  We are getting it from fdget(); what else can we get in flags there?

[PATCH 3/5] net: Set fput_needed iff FDPUT_FPUT is set

[linmiaohe]

From: Miaohe Lin <linmiaohe@huawei.com>

We should fput() file iff FDPUT_FPUT is set. So we should set fput_needed
accordingly.

Fixes: 00e188ef6a7e ("sockfd_lookup_light(): switch to fdget^W^Waway from fget_light")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 net/socket.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/socket.c b/net/socket.c
index 6aff5aeb6728..ee9c9dac4728 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -500,7 +500,7 @@ static struct socket *sockfd_lookup_light(int fd, int *err, int *fput_needed)
 	if (f.file) {
 		sock = sock_from_file(f.file, err);
 		if (likely(sock)) {
-			*fput_needed = f.flags;
+			*fput_needed = f.flags & FDPUT_FPUT;
 			return sock;
 		}
 		fdput(f);
-- 
2.19.1