netdev - [PATCH v2 36/63] scsi: ibmvscsi: Avoid multi-field memset() overflow by aiming at srp

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Date:   Tue, 17 Aug 2021 23:05:06 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-kernel@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Tyrel Datwyler <tyreld@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-staging@...ts.linux.dev,
        linux-block@...r.kernel.org, linux-kbuild@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-hardening@...r.kernel.org
Subject: [PATCH v2 36/63] scsi: ibmvscsi: Avoid multi-field memset() overflow by aiming at srp

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Instead of writing beyond the end of evt_struct->iu.srp.cmd, target the
upper union (evt_struct->iu.srp) instead, as that's what is being wiped.

Cc: Tyrel Datwyler <tyreld@...ux.ibm.com>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: "James E.J. Bottomley" <jejb@...ux.ibm.com>
Cc: "Martin K. Petersen" <martin.petersen@...cle.com>
Cc: linux-scsi@...r.kernel.org
Cc: linuxppc-dev@...ts.ozlabs.org
Signed-off-by: Kees Cook <keescook@...omium.org>
Acked-by: Martin K. Petersen <martin.petersen@...cle.com>
Link: https://lore.kernel.org/lkml/yq135rzp79c.fsf@ca-mkp.ca.oracle.com
Acked-by: Tyrel Datwyler <tyreld@...ux.ibm.com>
Link: https://lore.kernel.org/lkml/6eae8434-e9a7-aa74-628b-b515b3695359@linux.ibm.com
---
 drivers/scsi/ibmvscsi/ibmvscsi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/ibmvscsi/ibmvscsi.c b/drivers/scsi/ibmvscsi/ibmvscsi.c
index 50df7dd9cb91..ea8e01f49cba 100644
--- a/drivers/scsi/ibmvscsi/ibmvscsi.c
+++ b/drivers/scsi/ibmvscsi/ibmvscsi.c
@@ -1055,8 +1055,9 @@ static int ibmvscsi_queuecommand_lck(struct scsi_cmnd *cmnd,
 		return SCSI_MLQUEUE_HOST_BUSY;
 
 	/* Set up the actual SRP IU */
+	BUILD_BUG_ON(sizeof(evt_struct->iu.srp) != SRP_MAX_IU_LEN);
+	memset(&evt_struct->iu.srp, 0x00, sizeof(evt_struct->iu.srp));
 	srp_cmd = &evt_struct->iu.srp.cmd;
-	memset(srp_cmd, 0x00, SRP_MAX_IU_LEN);
 	srp_cmd->opcode = SRP_CMD;
 	memcpy(srp_cmd->cdb, cmnd->cmnd, sizeof(srp_cmd->cdb));
 	int_to_scsilun(lun, &srp_cmd->lun);
-- 
2.30.2