[067/181] mm/gup: protect unpin_user_pages() against npages==-ERRNO

Commit Message

Andrew Morton Oct. 13, 2020, 11:52 p.m. UTC

From: John Hubbard <[e-mail]>
Subject: mm/gup: protect unpin_user_pages() against npages==-ERRNO

As suggested by Dan Carpenter, fortify unpin_user_pages() just a bit,
against a typical caller mistake: check if the npages arg is really a
-ERRNO value, which would blow up the unpinning loop: WARN and return.

If this new WARN_ON() fires, then the system *might* be leaking pages (by
leaving them pinned), but probably not.  More likely, gup/pup returned a
hard -ERRNO error to the caller, who erroneously passed it here.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: John Hubbard <[e-mail]>
Signed-off-by: Dan Carpenter <[e-mail]>
Cc: Ira Weiny <[e-mail]>
Cc: Souptick Joarder <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/gup.c |    7 +++++++
 1 file changed, 7 insertions(+)

Patch

--- a/mm/gup.c~mm-gup-protect-unpin_user_pages-against-npages==-errno
+++ a/mm/gup.c
@@ -329,6 +329,13 @@  void unpin_user_pages(struct page **page
 	unsigned long index;
 
 	/*
+	 * If this WARN_ON() fires, then the system *might* be leaking pages (by
+	 * leaving them pinned), but probably not. More likely, gup/pup returned
+	 * a hard -ERRNO error to the caller, who erroneously passed it here.
+	 */
+	if (WARN_ON(IS_ERR_VALUE(npages)))
+		return;
+	/*
 	 * TODO: this can be optimized for huge pages: if a series of pages is
 	 * physically contiguous and part of the same compound page, then a
 	 * single operation to the head page should suffice.