linux-kernel - Re: [PATCH] loop: fix backing file reference leak on validation error

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Message-ID: <199958bca6a.7ea76c7c550787.2798726002425326647@linux.beauty>
Date: Mon, 29 Sep 2025 20:56:30 +0800
From: Li Chen <me@...ux.beauty>
To: "Yu Kuai" <yukuai1@...weicloud.com>
Cc: "Jens Axboe" <axboe@...nel.dk>,
	"linux-block" <linux-block@...r.kernel.org>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"yukuai" <yukuai3@...wei.com>
Subject: Re: [PATCH] loop: fix backing file reference leak on validation
 error

Hi Yu,

 ---- On Mon, 29 Sep 2025 09:11:04 +0800  Yu Kuai <yukuai1@...weicloud.com> wrote --- 
 > Hi,
 > 
 > 在 2025/09/26 20:12, Li Chen 写道:
 > > loop_change_fd() and loop_configure() call loop_check_backing_file()
 > > to validate the new backing file. If validation fails, the reference
 > > acquired by fget() was not dropped, leaking a file reference.
 > > 
 > > Fix this by calling fput(file) before returning the error.
 > > 
 > > Signed-off-by: Li Chen <chenl311@...natelecom.cn>
 > > ---
 > >   drivers/block/loop.c | 8 ++++++--
 > >   1 file changed, 6 insertions(+), 2 deletions(-)
 > > 
 > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c
 > > index 053a086d547e..94ec7f747f36 100644
 > > --- a/drivers/block/loop.c
 > > +++ b/drivers/block/loop.c
 > > @@ -551,8 +551,10 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
 > >           return -EBADF;
 > >   
 > >       error = loop_check_backing_file(file);
 > > -    if (error)
 > > +    if (error) {
 > > +        fput(file);
 > >           return error;
 > > +    }
 > >   
 > >       /* suppress uevents while reconfiguring the device */
 > >       dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 1);
 > > @@ -993,8 +995,10 @@ static int loop_configure(struct loop_device *lo, blk_mode_t mode,
 > >           return -EBADF;
 > >   
 > >       error = loop_check_backing_file(file);
 > > -    if (error)
 > > +    if (error) {
 > > +        fput(file);
 > >           return error;
 > > +    }
 > >   
 > >       is_loop = is_loop_device(file);
 > >   
 > > 
 > 
 > The changes look correct, however, I'll prefer to change the error path
 > to the reverse order and add a new error tag.

Thanks, but I will switch to scope-based resource management in v2, as suggested by Markus.

Regards,
Li