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UPSTREAM: mm/memfd: make F_SEAL_FUTURE_WRITE seal more robust

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A better way to do F_SEAL_FUTURE_WRITE seal was discussed [1] last week
where we don't need to modify core VFS structures to get the same
behavior of the seal. This solves several side-effects pointed out by
Andy [2].

[1] https://lore.kernel.org/lkml/20181111173650.GA256781@google.com/
[2] https://lore.kernel.org/lkml/69CE06CC-E47C-4992-848A-66EB23EE6C74@amacapital.net/

Suggested-by: Andy Lutomirski <luto@kernel.org>
Fixes: 5e653c2923fd ("mm: Add an F_SEAL_FUTURE_WRITE seal to memfd")
Change-id: I5d2414cfcf8ac42d3632d0b0dc960c742d490e2f
Verified with test program at: https://lore.kernel.org/patchwork/patch/1008117/
Backport link: https://lore.kernel.org/patchwork/patch/1014892/
Bug: 113362644
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
This commit is contained in:
Joel Fernandes (Google) 2018-11-19 21:21:36 -08:00 committed by Joel Fernandes
parent 1dc8ca4429
commit 2e0d7ea44a
3 changed files with 22 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
fs/hugetlbfs/inode.c
View File

@ -530,7 +530,7 @@ static long hugetlbfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
inode_lock(inode);
/* protected by i_mutex */
if (info->seals & F_SEAL_WRITE) {
if (info->seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE)) {
inode_unlock(inode);
return -EPERM;
}

19
mm/memfd.c
View File

@ -220,25 +220,6 @@ static int memfd_add_seals(struct file *file, unsigned int seals)
}
}
if ((seals & F_SEAL_FUTURE_WRITE) &&
!(*file_seals & F_SEAL_FUTURE_WRITE)) {
/*
* The FUTURE_WRITE seal also prevents growing and shrinking
* so we need them to be already set, or requested now.
*/
int test_seals = (seals | *file_seals) &
(F_SEAL_GROW | F_SEAL_SHRINK);
if (test_seals != (F_SEAL_GROW | F_SEAL_SHRINK)) {
error = -EINVAL;
goto unlock;
}
spin_lock(&file->f_lock);
file->f_mode &= ~(FMODE_WRITE | FMODE_PWRITE);
spin_unlock(&file->f_lock);
}
*file_seals |= seals;
error = 0;

24
mm/shmem.c
View File

@ -2169,6 +2169,23 @@ int shmem_lock(struct file *file, int lock, struct user_struct *user)
static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
{
struct shmem_inode_info *info = SHMEM_I(file_inode(file));
/*
* New PROT_READ and MAP_SHARED mmaps are not allowed when "future
* write" seal active.
*/
if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE) &&
(info->seals & F_SEAL_FUTURE_WRITE))
return -EPERM;
/*
* Since the F_SEAL_FUTURE_WRITE seals allow for a MAP_SHARED read-only
* mapping, take care to not allow mprotect to revert protections.
*/
if (info->seals & F_SEAL_FUTURE_WRITE)
vma->vm_flags &= ~(VM_MAYWRITE);
file_accessed(file);
vma->vm_ops = &shmem_vm_ops;
if (IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE) &&
@ -2422,8 +2439,9 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
pgoff_t index = pos >> PAGE_SHIFT;
/* i_mutex is held by caller */
if (unlikely(info->seals & (F_SEAL_WRITE | F_SEAL_GROW))) {
if (info->seals & F_SEAL_WRITE)
if (unlikely(info->seals & (F_SEAL_GROW |
F_SEAL_WRITE | F_SEAL_FUTURE_WRITE))) {
if (info->seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE))
return -EPERM;
if ((info->seals & F_SEAL_GROW) && pos + len > inode->i_size)
return -EPERM;
@ -2686,7 +2704,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
DECLARE_WAIT_QUEUE_HEAD_ONSTACK(shmem_falloc_waitq);
/* protected by i_mutex */
if (info->seals & F_SEAL_WRITE) {
if (info->seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE)) {
error = -EPERM;
goto out;
}