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userfaultfd_release: always remove uffd flags and clear vm_userfaultfd_ctx

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userfaultfd_release() should clear vm_flags/vm_userfaultfd_ctx even if
mm->core_state != NULL.

Otherwise a page fault can see userfaultfd_missing() == T and use an
already freed userfaultfd_ctx.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: 04f5866e41 ("coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping")
Signed-off-by: Oleg Nesterov <[email protected]>
Reported-by: Kefeng Wang <[email protected]>
Reviewed-by: Andrea Arcangeli <[email protected]>
Tested-by: Kefeng Wang <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Tetsuo Handa <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Oleg Nesterov 2019-08-24 17:54:56 -07:00 • committed by Linus Torvalds
commit 46d0b24c5e
1 changed files with 13 additions and 12 deletions
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25
fs/userfaultfd.c
View file

@ -880,6 +880,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
/* len == 0 means wake all */
struct userfaultfd_wake_range range = { .len = 0, };
unsigned long new_flags;
bool still_valid;
WRITE_ONCE(ctx->released, true);
@ -895,8 +896,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
* taking the mmap_sem for writing.
*/
down_write(&mm->mmap_sem);
if (!mmget_still_valid(mm))
goto skip_mm;
still_valid = mmget_still_valid(mm);
prev = NULL;
for (vma = mm->mmap; vma; vma = vma->vm_next) {
cond_resched();
@ -907,19 +907,20 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
continue;
}
new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
new_flags, vma->anon_vma,
vma->vm_file, vma->vm_pgoff,
vma_policy(vma),
NULL_VM_UFFD_CTX);
if (prev)
vma = prev;
else
prev = vma;
if (still_valid) {
prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
new_flags, vma->anon_vma,
vma->vm_file, vma->vm_pgoff,
vma_policy(vma),
NULL_VM_UFFD_CTX);
if (prev)
vma = prev;
else
prev = vma;
}
vma->vm_flags = new_flags;
vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
}
skip_mm:
up_write(&mm->mmap_sem);
mmput(mm);
wakeup: