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authorMichael S. Tsirkin <[email protected]>2018-04-13 15:35:20 -0700
committerLinus Torvalds <[email protected]>2018-04-13 17:10:27 -0700
commitc61611f70958d86f659bca25c02ae69413747a8d (patch)
treeb3a07243bda97550d0f6b8700fcc6de7e34d4fe5
parent09e35a4a1ca8b9988ca9b8557d17948cd6c0808b (diff)
get_user_pages_fast(): return -EFAULT on access_ok failure
get_user_pages_fast is supposed to be a faster drop-in equivalent of get_user_pages. As such, callers expect it to return a negative return code when passed an invalid address, and never expect it to return 0 when passed a positive number of pages, since its documentation says: * Returns number of pages pinned. This may be fewer than the number * requested. If nr_pages is 0 or negative, returns 0. If no pages * were pinned, returns -errno. When get_user_pages_fast fall back on get_user_pages this is exactly what happens. Unfortunately the implementation is inconsistent: it returns 0 if passed a kernel address, confusing callers: for example, the following is pretty common but does not appear to do the right thing with a kernel address: ret = get_user_pages_fast(addr, 1, writeable, &page); if (ret < 0) return ret; Change get_user_pages_fast to return -EFAULT when supplied a kernel address to make it match expectations. All callers have been audited for consistency with the documented semantics. Link: http://lkml.kernel.org/r/[email protected] Fixes: 5b65c4677a57 ("mm, x86/mm: Fix performance regression in get_user_pages_fast()") Signed-off-by: Michael S. Tsirkin <[email protected]> Reported-by: [email protected] Reviewed-by: Andrew Morton <[email protected]> Cc: Kirill A. Shutemov <[email protected]> Cc: Huang Ying <[email protected]> Cc: Jonathan Corbet <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Thorsten Leemhuis <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
-rw-r--r--mm/gup.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/mm/gup.c b/mm/gup.c
index f296df6cf666..db5346f80a5a 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1806,9 +1806,12 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
len = (unsigned long) nr_pages << PAGE_SHIFT;
end = start + len;
+ if (nr_pages <= 0)
+ return 0;
+
if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
(void __user *)start, len)))
- return 0;
+ return -EFAULT;
if (gup_fast_permitted(start, nr_pages, write)) {
local_irq_disable();