uprobes: Refuse to insert a probe into MAP_SHARED vma

valid_vma() rejects the VM_SHARED vmas, but this still allows to insert
a probe into the MAP_SHARED but not VM_MAYWRITE vma.

Currently this is fine, such a mapping doesn't really differ from the
private read-only mmap except mprotect(PROT_WRITE) won't work. However,
get_user_pages(FOLL_WRITE | FOLL_FORCE) doesn't allow to COW in this
case, and it would be safer to follow the same conventions as mm even
if currently this happens to work.

After the recent cda540ace6a1 "mm: get_user_pages(write,force) refuse
to COW in shared areas" only uprobes can insert an anon page into the
shared file-backed area, lets stop this and change valid_vma() to check
VM_MAYSHARE instead.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index d1edc5e6fd03..7716c40f2c50 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -127,7 +127,7 @@ struct xol_area {
  */
 static bool valid_vma(struct vm_area_struct *vma, bool is_register)
 {
-        vm_flags_t flags = VM_HUGETLB | VM_MAYEXEC | VM_SHARED;
+        vm_flags_t flags = VM_HUGETLB | VM_MAYEXEC | VM_MAYSHARE;
 
         if (is_register)
                 flags |= VM_WRITE;