We used to not pass in the pgoff correctly when register/unregister uffd regions, it caused incorrect behavior on vma merging and can cause mergeable vmas being separate after ioctls return.

For example, when we have:

vma1(range 0-9, with uffd), vma2(range 10-19, no uffd)

Then someone unregisters uffd on range (5-9), it should logically become:

vma1(range 0-4, with uffd), vma2(range 5-19, no uffd)

But with current code we'll have:

vma1(range 0-4, with uffd), vma3(range 5-9, no uffd), vma2(range 10-19, no uffd)

This patch allows such merge to happen correctly before ioctl returns.

This behavior seems to have existed since the 1st day of uffd. Since pgoff for vma_merge() is only used to identify the possibility of vma merging, meanwhile here what we did was always passing in a pgoff smaller than what we should, so there should have no other side effect besides not merging it. Let's still tentatively copy stable for this, even though I don't see anything will go wrong besides vma being split (which is mostly not user visible).

Cc: Andrea Arcangeli aarcange@redhat.com Cc: Mike Rapoport (IBM) rppt@kernel.org Cc: linux-stable stable@vger.kernel.org Reported-by: Lorenzo Stoakes lstoakes@gmail.com Acked-by: Lorenzo Stoakes lstoakes@gmail.com Reviewed-by: Liam R. Howlett Liam.Howlett@oracle.com Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory externalization") Signed-off-by: Peter Xu peterx@redhat.com --- fs/userfaultfd.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 17c8c345dac4..4e800bb7d2ab 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -1332,6 +1332,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx, bool basic_ioctls; unsigned long start, end, vma_end; struct vma_iterator vmi; + pgoff_t pgoff;

user_uffdio_register = (struct uffdio_register __user *) arg;

@@ -1484,8 +1485,9 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx, vma_end = min(end, vma->vm_end);

new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags; + pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT); prev = vma_merge(&vmi, mm, prev, start, vma_end, new_flags, - vma->anon_vma, vma->vm_file, vma->vm_pgoff, + vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma), ((struct vm_userfaultfd_ctx){ ctx }), anon_vma_name(vma)); @@ -1565,6 +1567,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, unsigned long start, end, vma_end; const void __user *buf = (void __user *)arg; struct vma_iterator vmi; + pgoff_t pgoff;

ret = -EFAULT; if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister))) @@ -1667,8 +1670,9 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, uffd_wp_range(vma, start, vma_end - start, false);

new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS; + pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT); prev = vma_merge(&vmi, mm, prev, start, vma_end, new_flags, - vma->anon_vma, vma->vm_file, vma->vm_pgoff, + vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma), NULL_VM_UFFD_CTX, anon_vma_name(vma)); if (prev) {