queue-4.4/include-linux-swap.h-use-offsetof-instead-of-custom-.patch

   1 From 7169afce8a08816f34c321d1f15948a5d38c5fa8 Mon Sep 17 00:00:00 2001
   2 From: Pi-Hsun Shih <pihsun@chromium.org>
   3 Date: Wed, 13 Mar 2019 11:44:33 -0700
   4 Subject: include/linux/swap.h: use offsetof() instead of custom __swapoffset
   5  macro
   6
   7 [ Upstream commit a4046c06be50a4f01d435aa7fe57514818e6cc82 ]
   8
   9 Use offsetof() to calculate offset of a field to take advantage of
  10 compiler built-in version when possible, and avoid UBSAN warning when
  11 compiling with Clang:
  12
  13   UBSAN: Undefined behaviour in mm/swapfile.c:3010:38
  14   member access within null pointer of type 'union swap_header'
  15   CPU: 6 PID: 1833 Comm: swapon Tainted: G S                4.19.23 #43
  16   Call trace:
  17    dump_backtrace+0x0/0x194
  18    show_stack+0x20/0x2c
  19    __dump_stack+0x20/0x28
  20    dump_stack+0x70/0x94
  21    ubsan_epilogue+0x14/0x44
  22    ubsan_type_mismatch_common+0xf4/0xfc
  23    __ubsan_handle_type_mismatch_v1+0x34/0x54
  24    __se_sys_swapon+0x654/0x1084
  25    __arm64_sys_swapon+0x1c/0x24
  26    el0_svc_common+0xa8/0x150
  27    el0_svc_compat_handler+0x2c/0x38
  28    el0_svc_compat+0x8/0x18
  29
  30 Link: http://lkml.kernel.org/r/20190312081902.223764-1-pihsun@chromium.org
  31 Signed-off-by: Pi-Hsun Shih <pihsun@chromium.org>
  32 Acked-by: Michal Hocko <mhocko@suse.com>
  33 Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
  34 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  35 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  36 Signed-off-by: Sasha Levin <sashal@kernel.org>
  37 ---
  38  include/linux/swap.h |    4 ++--
  39  1 file changed, 2 insertions(+), 2 deletions(-)
  40
  41 --- a/include/linux/swap.h
  42 +++ b/include/linux/swap.h
  43 @@ -135,9 +135,9 @@ struct swap_extent {
  44  /*
  45   * Max bad pages in the new format..
  46   */
  47 -#define __swapoffset(x) ((unsigned long)&((union swap_header *)0)->x)
  48  #define MAX_SWAP_BADPAGES \
  49 -       ((__swapoffset(magic.magic) - __swapoffset(info.badpages)) / sizeof(int))
  50 +       ((offsetof(union swap_header, magic.magic) - \
  51 +         offsetof(union swap_header, info.badpages)) / sizeof(int))
  52
  53  enum {
  54         SWP_USED        = (1 << 0),     /* is slot in swap_info[] used? */