The patch titled
Subject: userfaultfd: shmem: handle coredumping in handle_userfault()
has been removed from the -mm tree. Its filename was
userfaultfd-shmem-handle-coredumping-in-handle_userfault.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Subject: userfaultfd: shmem: handle coredumping in handle_userfault()
Anon and hugetlbfs handle FOLL_DUMP set by get_dump_page() internally to
__get_user_pages().
shmem as opposed has no special FOLL_DUMP handling there so
handle_mm_fault() is invoked without mmap_sem and ends up calling
handle_userfault() that isn't expecting to be invoked without mmap_sem
held.
This makes handle_userfault() fail immediately if invoked through
shmem_vm_ops->fault during coredumping and solves the problem.
The side effect is a BUG_ON with no lock held triggered by the coredumping
process which exits. Only 4.11 is affected, pre-4.11 anon memory holes
are skipped in __get_user_pages by checking FOLL_DUMP explicitly against
empty pagetables (mm/gup.c:no_page_table()).
It's zero cost as we already had a check for current->flags to prevent
futex to trigger userfaults during exit (PF_EXITING).
Link: http://lkml.kernel.org/r/20170615214838.27429-1-aarcange@xxxxxxxxxx
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Reported-by: "Dr. David Alan Gilbert" <dgilbert@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.11+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/userfaultfd.c | 29 +++++++++++++++++++++--------
1 file changed, 21 insertions(+), 8 deletions(-)
diff -puN fs/userfaultfd.c~userfaultfd-shmem-handle-coredumping-in-handle_userfault fs/userfaultfd.c
--- a/fs/userfaultfd.c~userfaultfd-shmem-handle-coredumping-in-handle_userfault
+++ a/fs/userfaultfd.c
@@ -340,9 +340,28 @@ int handle_userfault(struct vm_fault *vm
bool must_wait, return_to_userland;
long blocking_state;
- BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
-
ret = VM_FAULT_SIGBUS;
+
+ /*
+ * We don't do userfault handling for the final child pid update.
+ *
+ * We also don't do userfault handling during
+ * coredumping. hugetlbfs has the special
+ * follow_hugetlb_page() to skip missing pages in the
+ * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
+ * the no_page_table() helper in follow_page_mask(), but the
+ * shmem_vm_ops->fault method is invoked even during
+ * coredumping without mmap_sem and it ends up here.
+ */
+ if (current->flags & (PF_EXITING|PF_DUMPCORE))
+ goto out;
+
+ /*
+ * Coredumping runs without mmap_sem so we can only check that
+ * the mmap_sem is held, if PF_DUMPCORE was not set.
+ */
+ WARN_ON_ONCE(!rwsem_is_locked(&mm->mmap_sem));
+
ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
if (!ctx)
goto out;
@@ -361,12 +380,6 @@ int handle_userfault(struct vm_fault *vm
goto out;
/*
- * We don't do userfault handling for the final child pid update.
- */
- if (current->flags & PF_EXITING)
- goto out;
-
- /*
* Check that we can return VM_FAULT_RETRY.
*
* NOTE: it should become possible to return VM_FAULT_RETRY
_
Patches currently in -mm which might be from aarcange@xxxxxxxxxx are
ksm-introduce-ksm_max_page_sharing-per-page-deduplication-limit.patch
ksm-fix-use-after-free-with-merge_across_nodes-=-0.patch
ksm-cleanup-stable_node-chain-collapse-case.patch
ksm-swap-the-two-output-parameters-of-chain-chain_prune.patch
ksm-optimize-refile-of-stable_node_dup-at-the-head-of-the-chain.patch