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

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This reverts commit 7c6893e3c9.

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

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Miklos Szeredi 2018-07-18 15:44:43 +02:00
parent d561f21856
commit 6742cee043
4 changed files with 9 additions and 70 deletions
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2
fs/internal.h
View File

@ -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

64
fs/namespace.c
View File

@ -431,18 +431,13 @@ int __mnt_want_write_file(struct file *file)
}
/**
* mnt_want_write_file_path - get write access to a file's mount
* 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
*
* 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 mnt_want_write_file(struct file *file)
{
int ret;
@ -452,53 +447,6 @@ int mnt_want_write_file_path(struct file *file)
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);
ret = __mnt_want_write_file(file);
if (ret)
sb_end_write(file_inode(file)->i_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);

4
fs/open.c
View File

@ -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:

9
fs/xattr.c
View File

@ -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;