amd64_edac:__amd64_set_scrub_rate(): avoid overindexing scrubrates[]

If none of the elements in scrubrates[] matches, this loop will cause
__amd64_set_scrub_rate() to incorrectly use the n+1th element.

As the function is designed to use the final scrubrates[] element in the
case of no match, we can fix this bug by simply terminating the array
search at the n-1th element.

Boris: this code is fragile anyway, see here why:
http://marc.info/?l=linux-kernel&m=135102834131236&w=2

It will be rewritten more robustly soonish.

Reported-by: Denis Kirjanov <kirjanov@gmail.com>
Cc: stable@vger.kernel.org
Cc: Doug Thompson <dougthompson@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>

1 files changed, 4 insertions, 7 deletions

diff --git a/drivers/edac/amd64_edac.c b/drivers/edac/amd64_edac.c
index 5a297a26211d..cc8e7c78a23c 100644
--- a/drivers/edac/amd64_edac.c
+++ b/drivers/edac/amd64_edac.c
@@ -170,8 +170,11 @@ static int __amd64_set_scrub_rate(struct pci_dev *ctl, u32 new_bw, u32 min_rate)
          * memory controller and apply to register. Search for the first
          * bandwidth entry that is greater or equal than the setting requested
          * and program that. If at last entry, turn off DRAM scrubbing.
+         *
+         * If no suitable bandwidth is found, turn off DRAM scrubbing entirely
+         * by falling back to the last element in scrubrates[].
          */
-        for (i = 0; i < ARRAY_SIZE(scrubrates); i++) {
+        for (i = 0; i < ARRAY_SIZE(scrubrates) - 1; i++) {
                 /*
                  * skip scrub rates which aren't recommended
                  * (see F10 BKDG, F3x58)
@@ -181,12 +184,6 @@ static int __amd64_set_scrub_rate(struct pci_dev *ctl, u32 new_bw, u32 min_rate)
 
                 if (scrubrates[i].bandwidth <= new_bw)
                         break;
-
-                /*
-                 * if no suitable bandwidth found, turn off DRAM scrubbing
-                 * entirely by falling back to the last element in the
-                 * scrubrates array.
-                 */
         }
 
         scrubval = scrubrates[i].scrubval;