libnvdimm: fix ars_status output length calculation

Commit 96c3d8a4e033 ("acpi, nfit, libnvdimm: fix / harden ars_status output length handling")
Introduced additional hardening for ambiguity in the ACPI spec for
ars_status output sizing. However, it had a couple of cases mixed up.
Where it should have been checking for (and returning) "out_field[1] -
4" it was using "out_field[1] - 8" and vice versa.

This caused a four byte discrepancy in the buffer size passed on to
the command handler, and in some cases, this caused memory corruption
like:

  ./daxdev-errors.sh: line 76: 24104 Aborted   (core dumped) ./daxdev-errors $busdev $region
  malloc(): memory corruption
  Program received signal SIGABRT, Aborted.
  [...]
  #5  0x00007ffff7865a2e in calloc () from /lib64/libc.so.6
  #6  0x00007ffff7bc2970 in ndctl_bus_cmd_new_ars_status (ars_cap=ars_cap@entry=0x6153b0) at ars.c:136
  #7  0x0000000000401644 in check_ars_status (check=0x7fffffffdeb0, bus=0x604c20) at daxdev-errors.c:144
  #8  test_daxdev_clear_error (region_name=<optimized out>, bus_name=<optimized out>)
      at daxdev-errors.c:332

Cc: <stable@vger.kernel.org>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Lukasz Dorau <lukasz.dorau@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Fixes: 96c3d8a4e033 ("acpi, nfit, libnvdimm: fix / harden ars_status output length handling")
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Signed-of-by: Dave Jiang <dave.jiang@intel.com>

diff --git a/drivers/nvdimm/bus.c b/drivers/nvdimm/bus.c
index 27902a8799b1e022049078efc2ce14269dbea672..8aae6dcc839fed90a76e31eaf35a5f47ac04957d 100644 (file)
--- a/drivers/nvdimm/bus.c
+++ b/drivers/nvdimm/bus.c
@@ -812,9 +812,9 @@ u32 nd_cmd_out_size(struct nvdimm *nvdimm, int cmd,
                 * overshoots the remainder by 4 bytes, assume it was
                 * including 'status'.
                 */
-               if (out_field[1] - 8 == remainder)
+               if (out_field[1] - 4 == remainder)
                        return remainder;
-               return out_field[1] - 4;
+               return out_field[1] - 8;
        } else if (cmd == ND_CMD_CALL) {
                struct nd_cmd_pkg *pkg = (struct nd_cmd_pkg *) in_field;