[PATCH v3] Fix srcu_struct node grpmask overflow on 64-bit systems

[Denis Arefev <arefev@swemel.ru>]

The value of an arithmetic expression 1 << (cpu - sdp->mynode->grplo)
is subject to overflow due to a failure to cast operands to a larger
data type before performing arithmetic.

The maximum result of this subtraction is defined by the RCU_FANOUT 
or other srcu level-spread values assigned by rcu_init_levelspread(), 
which can indeed cause the signed 32-bit integer literal ("1") to overflow 
when shifted by any value greater than 31. 

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Denis Arefev <arefev@swemel.ru>
---
v3: Changed the name of the patch, as suggested by 
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
v2: Added fixes to the srcu_schedule_cbs_snp function as suggested by 
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 kernel/rcu/srcutree.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 20d7a238d675..6c18e6005ae1 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -223,7 +223,7 @@ static bool init_srcu_struct_nodes(struct srcu_struct *ssp, gfp_t gfp_flags)
 				snp->grplo = cpu;
 			snp->grphi = cpu;
 		}
-		sdp->grpmask = 1 << (cpu - sdp->mynode->grplo);
+		sdp->grpmask = 1UL << (cpu - sdp->mynode->grplo);
 	}
 	smp_store_release(&ssp->srcu_sup->srcu_size_state, SRCU_SIZE_WAIT_BARRIER);
 	return true;
@@ -833,7 +833,7 @@ static void srcu_schedule_cbs_snp(struct srcu_struct *ssp, struct srcu_node *snp
 	int cpu;
 
 	for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {
-		if (!(mask & (1 << (cpu - snp->grplo))))
+		if (!(mask & (1UL << (cpu - snp->grplo))))
 			continue;
 		srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, cpu), delay);
 	}
-- 
2.25.1