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mm/hugetlb: fix F_SEAL_FUTURE_WRITE

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commit 22247efd822e6d263f3c8bd327f3f769aea9b1d9 upstream.

Patch series "mm/hugetlb: Fix issues on file sealing and fork", v2.

Hugh reported issue with F_SEAL_FUTURE_WRITE not applied correctly to
hugetlbfs, which I can easily verify using the memfd_test program, which
seems that the program is hardly run with hugetlbfs pages (as by default
shmem).

Meanwhile I found another probably even more severe issue on that hugetlb
fork won't wr-protect child cow pages, so child can potentially write to
parent private pages.  Patch 2 addresses that.

After this series applied, "memfd_test hugetlbfs" should start to pass.

This patch (of 2):

F_SEAL_FUTURE_WRITE is missing for hugetlb starting from the first day.
There is a test program for that and it fails constantly.

$ ./memfd_test hugetlbfs
memfd-hugetlb: CREATE
memfd-hugetlb: BASIC
memfd-hugetlb: SEAL-WRITE
memfd-hugetlb: SEAL-FUTURE-WRITE
mmap() didn't fail as expected
Aborted (core dumped)

I think it's probably because no one is really running the hugetlbfs test.

Fix it by checking FUTURE_WRITE also in hugetlbfs_file_mmap() as what we
do in shmem_mmap().  Generalize a helper for that.

Link: https://lkml.kernel.org/r/20210503234356.9097-1-peterx@redhat.com
Link: https://lkml.kernel.org/r/20210503234356.9097-2-peterx@redhat.com
Fixes: ab3948f58f ("mm/memfd: add an F_SEAL_FUTURE_WRITE seal to memfd")
Signed-off-by: Peter Xu <peterx@redhat.com>
Reported-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Xu
2021-05-14 17:27:04 -07:00
committed by Greg Kroah-Hartman
parent fe5c0a63ad
commit 014868616d
3 changed files with 41 additions and 18 deletions
Download Patch File Download Diff File Expand all files Collapse all files

32
include/linux/mm.h
View File

@@ -3178,5 +3178,37 @@ unsigned long wp_shared_mapping_range(struct address_space *mapping,
extern int sysctl_nr_trim_pages;
/**
* seal_check_future_write - Check for F_SEAL_FUTURE_WRITE flag and handle it
* @seals: the seals to check
* @vma: the vma to operate on
*
* Check whether F_SEAL_FUTURE_WRITE is set; if so, do proper check/handling on
* the vma flags. Return 0 if check pass, or <0 for errors.
*/
static inline int seal_check_future_write(int seals, struct vm_area_struct *vma)
{
if (seals & F_SEAL_FUTURE_WRITE) {
/*
* New PROT_WRITE and MAP_SHARED mmaps are not allowed when
* "future write" seal active.
*/
if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
return -EPERM;
/*
* Since an F_SEAL_FUTURE_WRITE sealed memfd can be mapped as
* MAP_SHARED and read-only, take care to not allow mprotect to
* revert protections on such mappings. Do this only for shared
* mappings. For private mappings, don't need to mask
* VM_MAYWRITE as we still want them to be COW-writable.
*/
if (vma->vm_flags & VM_SHARED)
vma->vm_flags &= ~(VM_MAYWRITE);
}
return 0;
}
#endif /* __KERNEL__ */
#endif /* _LINUX_MM_H */