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[PATCH][next] octeontx2-pf: Fix out-of-bounds read in otx2_get_fecparam()

From: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Date: 2021-02-12 12:26:42
Also in: linux-hardening, lkml
Subsystem: marvell octeontx2 physical function driver, networking drivers, the rest · Maintainers: Sunil Goutham, Geetha sowjanya, Ratheesh Kannoth, Subbaraya Sundeep, Bharat Bhushan, Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds

Code at line 967 implies that rsp->fwdata.supported_fec may be up to 4:

 967: if (rsp->fwdata.supported_fec <= FEC_MAX_INDEX)

If rsp->fwdata.supported_fec evaluates to 4, then there is an
out-of-bounds read at line 971 because fec is an array with
a maximum of 4 elements:

 954         const int fec[] = {
 955                 ETHTOOL_FEC_OFF,
 956                 ETHTOOL_FEC_BASER,
 957                 ETHTOOL_FEC_RS,
 958                 ETHTOOL_FEC_BASER | ETHTOOL_FEC_RS};
 959 #define FEC_MAX_INDEX 4

 971: fecparam->fec = fec[rsp->fwdata.supported_fec];

Fix this by properly indexing fec[] with rsp->fwdata.supported_fec - 1.
In this case the proper indexes 0 to 3 are used when
rsp->fwdata.supported_fec evaluates to a range of 1 to 4, correspondingly.

Fixes: d0cf9503e908 ("octeontx2-pf: ethtool fec mode support")
Addresses-Coverity-ID: 1501722 ("Out-of-bounds read")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/net/ethernet/marvell/octeontx2/nic/otx2_ethtool.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_ethtool.c b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_ethtool.c
index 237e5d3321d4..f7e8ada32a26 100644
--- a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_ethtool.c
+++ b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_ethtool.c
@@ -968,7 +968,7 @@ static int otx2_get_fecparam(struct net_device *netdev,
 		if (!rsp->fwdata.supported_fec)
 			fecparam->fec = ETHTOOL_FEC_NONE;
 		else
-			fecparam->fec = fec[rsp->fwdata.supported_fec];
+			fecparam->fec = fec[rsp->fwdata.supported_fec - 1];
 	}
 	return 0;
 }
-- 
2.27.0
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