4.20-stable review patch. If anyone has any objections, please let me know.
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[ Upstream commit 3cfd22be0ad663248fadfc8f6ffa3e255c394552 ]
When the process being tracked does mremap() without UFFD_FEATURE_EVENT_REMAP on the corresponding tracking uffd file handle, we should not generate the remap event, and at the same time we should clear all the uffd flags on the new VMA. Without this patch, we can still have the VM_UFFD_MISSING|VM_UFFD_WP flags on the new VMA even the fault handling process does not even know the existance of the VMA.
Link: http://lkml.kernel.org/r/20181211053409.20317-1-peterx@redhat.com Signed-off-by: Peter Xu peterx@redhat.com Reviewed-by: Andrea Arcangeli aarcange@redhat.com Acked-by: Mike Rapoport rppt@linux.vnet.ibm.com Reviewed-by: William Kucharski william.kucharski@oracle.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: Mike Rapoport rppt@linux.vnet.ibm.com Cc: Kirill A. Shutemov kirill@shutemov.name Cc: Hugh Dickins hughd@google.com Cc: Pavel Emelyanov xemul@virtuozzo.com Cc: Pravin Shedge pravin.shedge4linux@gmail.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/userfaultfd.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 7a85e609fc27..d8b8323e80f4 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -736,10 +736,18 @@ void mremap_userfaultfd_prep(struct vm_area_struct *vma, struct userfaultfd_ctx *ctx;
ctx = vma->vm_userfaultfd_ctx.ctx; - if (ctx && (ctx->features & UFFD_FEATURE_EVENT_REMAP)) { + + if (!ctx) + return; + + if (ctx->features & UFFD_FEATURE_EVENT_REMAP) { vm_ctx->ctx = ctx; userfaultfd_ctx_get(ctx); WRITE_ONCE(ctx->mmap_changing, true); + } else { + /* Drop uffd context if remap feature not enabled */ + vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; + vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING); } }