[PATCH 1/2] fs: unreference path on file close
Ahmad Fatoum
a.fatoum at pengutronix.de
Tue Jun 24 04:36:56 PDT 2025
Hi,
On 6/11/25 13:56, Sascha Hauer wrote:
> Since commit 83ffe89840e8 ("fs: use filename_create/filename_lookup
> instead of open-coding") we no longer open-code the file lookup during
> openat(). Unlike the open-coded variant filename_lookup() keeps a
> reference to the file which is now leaked and the filesystem cannot be
> unmounted anymore:
>
> umount: Device or resource busy
>
> Since commit a1da0079d162 ("fs: implement opendir in terms of fdopendir")
> this also happens when just a directory is opened.
>
> The original code was not quite correct: After calling terminate_walk()
> we no longer held a reference to the path for an opened file. Transfer
> the path to the already existing f_path in struct file and unreference
> it a close() time.
Unfortunately, this introduced a regression to v2025.06.0:
Before:
barebox at TI AM335x BeagleBone black:/ rm /mnt/mmc0.0/barebox.env
barebox at TI AM335x BeagleBone black:/ saveenv
saving environment to /mnt/mmc0.0/barebox.env
barebox at TI AM335x BeagleBone black:/ saveenv
saving environment to /mnt/mmc0.0/barebox.env
After:
barebox at TI AM335x BeagleBone black:/ rm /mnt/mmc0.0/barebox.env
barebox at TI AM335x BeagleBone black:/ saveenv
saving environment to /mnt/mmc0.0/barebox.env
could not open /mnt/mmc0.0/barebox.env: Invalid argument
saveenv: Invalid argument
barebox at TI AM335x BeagleBone black:/ saveenv
saving environment to /mnt/mmc0.0/barebox.env
The -EINVAL comes from fat_open being called with / as filename.
I am not yet sure what the proper fix is. At least we have a test
now to avoid the old regression from reocurring...
Cheers,
Ahmad
>
> Fixes: 83ffe89840e8 ("fs: use filename_create/filename_lookup instead of open-coding")
> Fixes: a1da0079d162 ("fs: implement opendir in terms of fdopendir")
> Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
> ---
> fs/fs.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/fs/fs.c b/fs/fs.c
> index d401268c1e..18343552a7 100644
> --- a/fs/fs.c
> +++ b/fs/fs.c
> @@ -330,7 +330,7 @@ static void put_file(struct file *f)
> f->path = NULL;
> f->fsdev = NULL;
> iput(f->f_inode);
> - dput(f->f_dentry);
> + path_put(&f->f_path);
> }
>
> static struct file *fd_to_file(int fd, bool o_path_ok)
> @@ -2550,7 +2550,7 @@ int openat(int dirfd, const char *pathname, int flags)
> int error = 0;
> struct inode *inode = NULL;
> struct dentry *dentry = NULL;
> - struct path path;
> + struct path path = {};
>
> if (flags & O_TMPFILE) {
> error = filename_lookup(dirfd, getname(pathname), LOOKUP_DIRECTORY, &path);
> @@ -2628,11 +2628,12 @@ int openat(int dirfd, const char *pathname, int flags)
> f = get_file(fsdev);
> if (!f) {
> error = -EMFILE;
> + path_put(&path);
> goto out1;
> }
>
> f->path = dpath(dentry, d_root);
> - f->f_dentry = dentry;
> + f->f_path = path;
> f->f_inode = iget(inode);
> f->f_flags = flags;
>
--
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