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

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From: John Hubbard <jhubbard@xxxxxxxxxx>
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/20200917065706.409079-1-jhubbard@xxxxxxxxxx
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: Souptick Joarder <jrdr.linux@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

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

--- 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.
_




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