sched/autogroup: Fix possible Spectre-v1 indexing for sched_prio_to_weight[]

> kernel/sched/autogroup.c:230 proc_sched_autogroup_set_nice() warn: potential spectre issue 'sched_prio_to_weight'

Userspace controls @nice, sanitize the array index.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/kernel/sched/autogroup.c b/kernel/sched/autogroup.c
index 6be6c575b6cd..2d4ff5353ded 100644
--- a/kernel/sched/autogroup.c
+++ b/kernel/sched/autogroup.c
@@ -2,6 +2,7 @@
 /*
  * Auto-group scheduling implementation:
  */
+#include <linux/nospec.h>
 #include "sched.h"
 
 unsigned int __read_mostly sysctl_sched_autogroup_enabled = 1;
@@ -209,7 +210,7 @@ int proc_sched_autogroup_set_nice(struct task_struct *p, int nice)
         static unsigned long next = INITIAL_JIFFIES;
         struct autogroup *ag;
         unsigned long shares;
-        int err;
+        int err, idx;
 
         if (nice < MIN_NICE || nice > MAX_NICE)
                 return -EINVAL;
@@ -227,7 +228,9 @@ int proc_sched_autogroup_set_nice(struct task_struct *p, int nice)
 
         next = HZ / 10 + jiffies;
         ag = autogroup_task_get(p);
-        shares = scale_load(sched_prio_to_weight[nice + 20]);
+
+        idx = array_index_nospec(nice + 20, 40);
+        shares = scale_load(sched_prio_to_weight[idx]);
 
         down_write(&ag->lock);
         err = sched_group_set_shares(ag->tg, shares);