[PATCH 6.1 197/197] userfaultfd: fix mmap_changing checking in mfill_atomic_hugetlb

Greg Kroah-Hartman
2024-02-20T21:08:38Z

From: Lokesh Gidra <lokeshgidra@google.com>

commit 67695f18d55924b2013534ef3bdc363bc9e14605 upstream.

In mfill_atomic_hugetlb(), mmap_changing isn't being checked
again if we drop mmap_lock and reacquire it. When the lock is not held,
mmap_changing could have been incremented. This is also inconsistent
with the behavior in mfill_atomic().

Link: https://lkml.kernel.org/r/20240117223729.1444522-1-lokeshgidra@google.com
Fixes: df2cc96e77011 ("userfaultfd: prevent non-cooperative events vs mcopy_atomic races")
Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nicolas Geoffray <ngeoffray@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/userfaultfd.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)

--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -327,6 +327,7 @@ static __always_inline ssize_t __mcopy_a
unsigned long dst_start,
unsigned long src_start,
unsigned long len,
+ atomic_t *mmap_changing,
enum mcopy_atomic_mode mode,
bool wp_copy)
{
@@ -445,6 +446,15 @@ retry:
goto out;
}
mmap_read_lock(dst_mm);
+ /*
+ * If memory mappings are changing because of non-cooperative
+ * operation (e.g. mremap) running in parallel, bail out and
+ * request the user to retry later
+ */
+ if (mmap_changing && atomic_read(mmap_changing)) {
+ err = -EAGAIN;
+ break;
+ }

dst_vma = NULL;
goto retry;
@@ -480,6 +490,7 @@ extern ssize_t __mcopy_atomic_hugetlb(st
unsigned long dst_start,
unsigned long src_start,
unsigned long len,
+ atomic_t *mmap_changing,
enum mcopy_atomic_mode mode,
bool wp_copy);
#endif /* CONFIG_HUGETLB_PAGE */
@@ -601,8 +612,8 @@ retry:
*/
if (is_vm_hugetlb_page(dst_vma))
return __mcopy_atomic_hugetlb(dst_mm, dst_vma, dst_start,
- src_start, len, mcopy_mode,
- wp_copy);
+ src_start, len, mmap_changing,
+ mcopy_mode, wp_copy);

if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
goto out_unlock;