Unverified Commit 83bc1d29 authored by Amir Goldstein's avatar Amir Goldstein Committed by Christian Brauner
Browse files

fs: get mnt_writers count for an open backing file's real path 



A writeable mapped backing file can perform writes to the real inode.
Therefore, the real path mount must be kept writable so long as the
writable map exists.

This may not be strictly needed for ovelrayfs private upper mount,
but it is correct to take the mnt_writers count in the vfs helper.

Signed-off-by: default avatarAmir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/r/20231009153712.1566422-2-amir73il@gmail.com


Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 6c4d1c99

fs/internal.h

+9 −2
Original line number Diff line number Diff line
@@ -96,13 +96,20 @@ struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred); 
struct file *alloc_empty_backing_file(int flags, const struct cred *cred);

void release_empty_file(struct file *f);



static inline void file_put_write_access(struct file *file)

{

	put_write_access(file->f_inode);

	mnt_put_write_access(file->f_path.mnt);

	if (unlikely(file->f_mode & FMODE_BACKING))

		mnt_put_write_access(backing_file_real_path(file)->mnt);

}



static inline void put_file_access(struct file *file)

{

	if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) {

		i_readcount_dec(file->f_inode);

	} else if (file->f_mode & FMODE_WRITER) {

		put_write_access(file->f_inode);

		mnt_put_write_access(file->f_path.mnt);

		file_put_write_access(file);

	}

}

fs/open.c

+25 −6
Original line number Diff line number Diff line
@@ -870,6 +870,30 @@ SYSCALL_DEFINE3(fchown, unsigned int, fd, uid_t, user, gid_t, group) 
	return ksys_fchown(fd, user, group);

}



static inline int file_get_write_access(struct file *f)

{

	int error;



	error = get_write_access(f->f_inode);

	if (unlikely(error))

		return error;

	error = mnt_get_write_access(f->f_path.mnt);

	if (unlikely(error))

		goto cleanup_inode;

	if (unlikely(f->f_mode & FMODE_BACKING)) {

		error = mnt_get_write_access(backing_file_real_path(f)->mnt);

		if (unlikely(error))

			goto cleanup_mnt;

	}

	return 0;



cleanup_mnt:

	mnt_put_write_access(f->f_path.mnt);

cleanup_inode:

	put_write_access(f->f_inode);

	return error;

}



static int do_dentry_open(struct file *f,

			  struct inode *inode,

			  int (*open)(struct inode *, struct file *))
@@ -892,14 +916,9 @@ static int do_dentry_open(struct file *f, 
	if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) {

		i_readcount_inc(inode);

	} else if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {

		error = get_write_access(inode);

		error = file_get_write_access(f);

		if (unlikely(error))

			goto cleanup_file;

		error = mnt_get_write_access(f->f_path.mnt);

		if (unlikely(error)) {

			put_write_access(inode);

			goto cleanup_file;

		}

		f->f_mode |= FMODE_WRITER;

	}