linux/fs/ramfs/file-nommu.c
Christian Brauner 549c729771
fs: make helpers idmap mount aware
Extend some inode methods with an additional user namespace argument. A
filesystem that is aware of idmapped mounts will receive the user
namespace the mount has been marked with. This can be used for
additional permission checking and also to enable filesystems to
translate between uids and gids if they need to. We have implemented all
relevant helpers in earlier patches.

As requested we simply extend the exisiting inode method instead of
introducing new ones. This is a little more code churn but it's mostly
mechanical and doesnt't leave us with additional inode methods.

Link: https://lore.kernel.org/r/20210121131959.646623-25-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-24 14:27:20 +01:00

266 lines
6.7 KiB
C

// SPDX-License-Identifier: GPL-2.0-or-later
/* file-nommu.c: no-MMU version of ramfs
*
* Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*/
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/backing-dev.h>
#include <linux/ramfs.h>
#include <linux/pagevec.h>
#include <linux/mman.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include "internal.h"
static int ramfs_nommu_setattr(struct user_namespace *, struct dentry *, struct iattr *);
static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
unsigned long addr,
unsigned long len,
unsigned long pgoff,
unsigned long flags);
static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma);
static unsigned ramfs_mmap_capabilities(struct file *file)
{
return NOMMU_MAP_DIRECT | NOMMU_MAP_COPY | NOMMU_MAP_READ |
NOMMU_MAP_WRITE | NOMMU_MAP_EXEC;
}
const struct file_operations ramfs_file_operations = {
.mmap_capabilities = ramfs_mmap_capabilities,
.mmap = ramfs_nommu_mmap,
.get_unmapped_area = ramfs_nommu_get_unmapped_area,
.read_iter = generic_file_read_iter,
.write_iter = generic_file_write_iter,
.fsync = noop_fsync,
.splice_read = generic_file_splice_read,
.splice_write = iter_file_splice_write,
.llseek = generic_file_llseek,
};
const struct inode_operations ramfs_file_inode_operations = {
.setattr = ramfs_nommu_setattr,
.getattr = simple_getattr,
};
/*****************************************************************************/
/*
* add a contiguous set of pages into a ramfs inode when it's truncated from
* size 0 on the assumption that it's going to be used for an mmap of shared
* memory
*/
int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
{
unsigned long npages, xpages, loop;
struct page *pages;
unsigned order;
void *data;
int ret;
gfp_t gfp = mapping_gfp_mask(inode->i_mapping);
/* make various checks */
order = get_order(newsize);
if (unlikely(order >= MAX_ORDER))
return -EFBIG;
ret = inode_newsize_ok(inode, newsize);
if (ret)
return ret;
i_size_write(inode, newsize);
/* allocate enough contiguous pages to be able to satisfy the
* request */
pages = alloc_pages(gfp, order);
if (!pages)
return -ENOMEM;
/* split the high-order page into an array of single pages */
xpages = 1UL << order;
npages = (newsize + PAGE_SIZE - 1) >> PAGE_SHIFT;
split_page(pages, order);
/* trim off any pages we don't actually require */
for (loop = npages; loop < xpages; loop++)
__free_page(pages + loop);
/* clear the memory we allocated */
newsize = PAGE_SIZE * npages;
data = page_address(pages);
memset(data, 0, newsize);
/* attach all the pages to the inode's address space */
for (loop = 0; loop < npages; loop++) {
struct page *page = pages + loop;
ret = add_to_page_cache_lru(page, inode->i_mapping, loop,
gfp);
if (ret < 0)
goto add_error;
/* prevent the page from being discarded on memory pressure */
SetPageDirty(page);
SetPageUptodate(page);
unlock_page(page);
put_page(page);
}
return 0;
add_error:
while (loop < npages)
__free_page(pages + loop++);
return ret;
}
/*****************************************************************************/
/*
*
*/
static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size)
{
int ret;
/* assume a truncate from zero size is going to be for the purposes of
* shared mmap */
if (size == 0) {
if (unlikely(newsize >> 32))
return -EFBIG;
return ramfs_nommu_expand_for_mapping(inode, newsize);
}
/* check that a decrease in size doesn't cut off any shared mappings */
if (newsize < size) {
ret = nommu_shrink_inode_mappings(inode, size, newsize);
if (ret < 0)
return ret;
}
truncate_setsize(inode, newsize);
return 0;
}
/*****************************************************************************/
/*
* handle a change of attributes
* - we're specifically interested in a change of size
*/
static int ramfs_nommu_setattr(struct user_namespace *mnt_userns,
struct dentry *dentry, struct iattr *ia)
{
struct inode *inode = d_inode(dentry);
unsigned int old_ia_valid = ia->ia_valid;
int ret = 0;
/* POSIX UID/GID verification for setting inode attributes */
ret = setattr_prepare(&init_user_ns, dentry, ia);
if (ret)
return ret;
/* pick out size-changing events */
if (ia->ia_valid & ATTR_SIZE) {
loff_t size = inode->i_size;
if (ia->ia_size != size) {
ret = ramfs_nommu_resize(inode, ia->ia_size, size);
if (ret < 0 || ia->ia_valid == ATTR_SIZE)
goto out;
} else {
/* we skipped the truncate but must still update
* timestamps
*/
ia->ia_valid |= ATTR_MTIME|ATTR_CTIME;
}
}
setattr_copy(&init_user_ns, inode, ia);
out:
ia->ia_valid = old_ia_valid;
return ret;
}
/*****************************************************************************/
/*
* try to determine where a shared mapping can be made
* - we require that:
* - the pages to be mapped must exist
* - the pages be physically contiguous in sequence
*/
static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
unsigned long addr, unsigned long len,
unsigned long pgoff, unsigned long flags)
{
unsigned long maxpages, lpages, nr, loop, ret;
struct inode *inode = file_inode(file);
struct page **pages = NULL, **ptr, *page;
loff_t isize;
/* the mapping mustn't extend beyond the EOF */
lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
isize = i_size_read(inode);
ret = -ENOSYS;
maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
if (pgoff >= maxpages)
goto out;
if (maxpages - pgoff < lpages)
goto out;
/* gang-find the pages */
pages = kcalloc(lpages, sizeof(struct page *), GFP_KERNEL);
if (!pages)
goto out_free;
nr = find_get_pages_contig(inode->i_mapping, pgoff, lpages, pages);
if (nr != lpages)
goto out_free_pages; /* leave if some pages were missing */
/* check the pages for physical adjacency */
ptr = pages;
page = *ptr++;
page++;
for (loop = lpages; loop > 1; loop--)
if (*ptr++ != page++)
goto out_free_pages;
/* okay - all conditions fulfilled */
ret = (unsigned long) page_address(pages[0]);
out_free_pages:
ptr = pages;
for (loop = nr; loop > 0; loop--)
put_page(*ptr++);
out_free:
kfree(pages);
out:
return ret;
}
/*****************************************************************************/
/*
* set up a mapping for shared memory segments
*/
static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)
{
if (!(vma->vm_flags & (VM_SHARED | VM_MAYSHARE)))
return -ENOSYS;
file_accessed(file);
vma->vm_ops = &generic_file_vm_ops;
return 0;
}