Commit 6742cee0 authored by Miklos Szeredi's avatar Miklos Szeredi
Browse files

Revert "ovl: don't allow writing ioctl on lower layer" 



This reverts commit 7c6893e3.

Overlayfs no longer relies on the vfs for checking writability of files.

Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
parent d561f218

fs/internal.h

+0 −2
Original line number Diff line number Diff line
@@ -80,10 +80,8 @@ extern void __init mnt_init(void); 


extern int __mnt_want_write(struct vfsmount *);

extern int __mnt_want_write_file(struct file *);

extern int mnt_want_write_file_path(struct file *);

extern void __mnt_drop_write(struct vfsmount *);

extern void __mnt_drop_write_file(struct file *);

extern void mnt_drop_write_file_path(struct file *);



/*

 * fs_struct.c

fs/namespace.c

+3 −61
Original line number Diff line number Diff line
@@ -430,73 +430,21 @@ int __mnt_want_write_file(struct file *file) 
		return mnt_clone_write(file->f_path.mnt);

}



/**

 * mnt_want_write_file_path - get write access to a file's mount

 * @file: the file who's mount on which to take a write

 *

 * This is like mnt_want_write, but it takes a file and can

 * do some optimisations if the file is open for write already

 *

 * Called by the vfs for cases when we have an open file at hand, but will do an

 * inode operation on it (important distinction for files opened on overlayfs,

 * since the file operations will come from the real underlying file, while

 * inode operations come from the overlay).

 */

int mnt_want_write_file_path(struct file *file)

{

	int ret;



	sb_start_write(file->f_path.mnt->mnt_sb);

	ret = __mnt_want_write_file(file);

	if (ret)

		sb_end_write(file->f_path.mnt->mnt_sb);

	return ret;

}



static inline int may_write_real(struct file *file)

{

	struct dentry *dentry = file->f_path.dentry;

	struct dentry *upperdentry;



	/* Writable file? */

	if (file->f_mode & FMODE_WRITER)

		return 0;



	/* Not overlayfs? */

	if (likely(!(dentry->d_flags & DCACHE_OP_REAL)))

		return 0;



	/* File refers to upper, writable layer? */

	upperdentry = d_real(dentry, NULL, 0, D_REAL_UPPER);

	if (upperdentry && file_inode(file) == d_inode(upperdentry))

		return 0;



	/* Lower layer: can't write to real file, sorry... */

	return -EPERM;

}



/**

 * mnt_want_write_file - get write access to a file's mount

 * @file: the file who's mount on which to take a write

 *

 * This is like mnt_want_write, but it takes a file and can

 * do some optimisations if the file is open for write already

 *

 * Mostly called by filesystems from their ioctl operation before performing

 * modification.  On overlayfs this needs to check if the file is on a read-only

 * lower layer and deny access in that case.

 */

int mnt_want_write_file(struct file *file)

{

	int ret;



	ret = may_write_real(file);

	if (!ret) {

		sb_start_write(file_inode(file)->i_sb);

	sb_start_write(file->f_path.mnt->mnt_sb);

	ret = __mnt_want_write_file(file);

	if (ret)

			sb_end_write(file_inode(file)->i_sb);

	}

		sb_end_write(file->f_path.mnt->mnt_sb);

	return ret;

}

EXPORT_SYMBOL_GPL(mnt_want_write_file);
@@ -536,15 +484,9 @@ void __mnt_drop_write_file(struct file *file) 
	__mnt_drop_write(file->f_path.mnt);

}



void mnt_drop_write_file_path(struct file *file)

{

	mnt_drop_write(file->f_path.mnt);

}



void mnt_drop_write_file(struct file *file)

{

	__mnt_drop_write(file->f_path.mnt);

	sb_end_write(file_inode(file)->i_sb);

	mnt_drop_write(file->f_path.mnt);

}

EXPORT_SYMBOL(mnt_drop_write_file);

fs/open.c

+2 −2
Original line number Diff line number Diff line
@@ -707,12 +707,12 @@ int ksys_fchown(unsigned int fd, uid_t user, gid_t group) 
	if (!f.file)

		goto out;



	error = mnt_want_write_file_path(f.file);

	error = mnt_want_write_file(f.file);

	if (error)

		goto out_fput;

	audit_file(f.file);

	error = chown_common(&f.file->f_path, user, group);

	mnt_drop_write_file_path(f.file);

	mnt_drop_write_file(f.file);

out_fput:

	fdput(f);

out:

fs/xattr.c

+4 −5
Original line number Diff line number Diff line
@@ -23,7 +23,6 @@ 
#include <linux/posix_acl_xattr.h>



#include <linux/uaccess.h>

#include "internal.h"



static const char *

strcmp_prefix(const char *a, const char *a_prefix)
@@ -501,10 +500,10 @@ SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name, 
	if (!f.file)

		return error;

	audit_file(f.file);

	error = mnt_want_write_file_path(f.file);

	error = mnt_want_write_file(f.file);

	if (!error) {

		error = setxattr(f.file->f_path.dentry, name, value, size, flags);

		mnt_drop_write_file_path(f.file);

		mnt_drop_write_file(f.file);

	}

	fdput(f);

	return error;
@@ -733,10 +732,10 @@ SYSCALL_DEFINE2(fremovexattr, int, fd, const char __user *, name) 
	if (!f.file)

		return error;

	audit_file(f.file);

	error = mnt_want_write_file_path(f.file);

	error = mnt_want_write_file(f.file);

	if (!error) {

		error = removexattr(f.file->f_path.dentry, name);

		mnt_drop_write_file_path(f.file);

		mnt_drop_write_file(f.file);

	}

	fdput(f);

	return error;

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