linux-kernel - [PATCH 5.10 093/199] RDMA/umem: Avoid undefined behavior of rounddown_pow_of

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Date:   Mon, 25 Jan 2021 19:38:35 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Aharon Landau <aharonl@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Maor Gottlieb <maorg@...lanox.com>,
        Leon Romanovsky <leonro@...dia.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.10 093/199] RDMA/umem: Avoid undefined behavior of rounddown_pow_of_two()

From: Aharon Landau <aharonl@...dia.com>

[ Upstream commit b79f2dc5ffe17b03ec8c55f0d63f65e87bcac676 ]

rounddown_pow_of_two() is undefined when the input is 0. Therefore we need
to avoid it in ib_umem_find_best_pgsz and return 0.  Otherwise, it could
result in not rejecting an invalid page size which eventually causes a
kernel oops due to the logical inconsistency.

Fixes: 3361c29e9279 ("RDMA/umem: Use simpler logic for ib_umem_find_best_pgsz()")
Link: https://lore.kernel.org/r/20210113121703.559778-2-leon@kernel.org
Signed-off-by: Aharon Landau <aharonl@...dia.com>
Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
Reviewed-by: Maor Gottlieb <maorg@...lanox.com>
Signed-off-by: Leon Romanovsky <leonro@...dia.com>
Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/infiniband/core/umem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index e9fecbdf391bc..5157ae29a4460 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -126,7 +126,7 @@ unsigned long ib_umem_find_best_pgsz(struct ib_umem *umem,
 	 */
 	if (mask)
 		pgsz_bitmap &= GENMASK(count_trailing_zeros(mask), 0);
-	return rounddown_pow_of_two(pgsz_bitmap);
+	return pgsz_bitmap ? rounddown_pow_of_two(pgsz_bitmap) : 0;
 }
 EXPORT_SYMBOL(ib_umem_find_best_pgsz);
 
-- 
2.27.0