linux-kernel - [PATCH v2] scsi: zfcp: Replace strlcpy() with strscpy()

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Message-Id: <20231130204056.it.978-kees@kernel.org>
Date:   Thu, 30 Nov 2023 12:41:00 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     Kees Cook <keescook@...omium.org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Steffen Maier <maier@...ux.ibm.com>,
        Benjamin Block <bblock@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Azeem Shaikh <azeemshaikh38@...il.com>,
        linux-s390@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH v2] scsi: zfcp: Replace strlcpy() with strscpy()

strlcpy() reads the entire source buffer first. This read may exceed
the destination size limit. This is both inefficient and can lead
to linear read overflows if a source string is not NUL-terminated[1].
Additionally, it returns the size of the source string, not the
resulting size of the destination string. In an effort to remove strlcpy()
completely[2], replace strlcpy() here with strscpy().

Overflow should be impossible here, but actually check for buffer sizes
being identical with BUILD_BUG_ON(), and include a run-time check as
well.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy [1]
Link: https://github.com/KSPP/linux/issues/89 [2]
Cc: "Martin K. Petersen" <martin.petersen@...cle.com>
Cc: "James E.J. Bottomley" <jejb@...ux.ibm.com>
Cc: Steffen Maier <maier@...ux.ibm.com>
Cc: Benjamin Block <bblock@...ux.ibm.com>
Cc: Heiko Carstens <hca@...ux.ibm.com>
Cc: Vasily Gorbik <gor@...ux.ibm.com>
Cc: Alexander Gordeev <agordeev@...ux.ibm.com>
Cc: Christian Borntraeger <borntraeger@...ux.ibm.com>
Cc: Sven Schnelle <svens@...ux.ibm.com>
Cc: Azeem Shaikh <azeemshaikh38@...il.com>
Cc: linux-s390@...r.kernel.org
Cc: linux-scsi@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 v2:
 - add BUILD_BUG_ON (bblock)
 - CC SCSI maintainers (bblock)
 v1: https://lore.kernel.org/all/20231116191435.work.581-kees@kernel.org/
---
 drivers/s390/scsi/zfcp_fc.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/scsi/zfcp_fc.c b/drivers/s390/scsi/zfcp_fc.c
index 4f0d0e55f0d4..d6516ab00437 100644
--- a/drivers/s390/scsi/zfcp_fc.c
+++ b/drivers/s390/scsi/zfcp_fc.c
@@ -900,8 +900,19 @@ static void zfcp_fc_rspn(struct zfcp_adapter *adapter,
 	zfcp_fc_ct_ns_init(&rspn_req->ct_hdr, FC_NS_RSPN_ID,
 			   FC_SYMBOLIC_NAME_SIZE);
 	hton24(rspn_req->rspn.fr_fid.fp_fid, fc_host_port_id(shost));
-	len = strlcpy(rspn_req->rspn.fr_name, fc_host_symbolic_name(shost),
-		      FC_SYMBOLIC_NAME_SIZE);
+
+	BUILD_BUG_ON(sizeof(rspn_req->name) !=
+			sizeof(fc_host_symbolic_name(shost)));
+	BUILD_BUG_ON(sizeof(rspn_req->name) !=
+			type_max(typeof(rspn_req->rspn.fr_name_len)) + 1);
+	len = strscpy(rspn_req->name, fc_host_symbolic_name(shost),
+		      sizeof(rspn_req->name));
+	/*
+	 * It should be impossible for this to truncate (see BUILD_BUG_ON()
+	 * above), but be robust anyway.
+	 */
+	if (WARN_ON(len < 0))
+		len = sizeof(rspn_req->name) - 1;
 	rspn_req->rspn.fr_name_len = len;
 
 	sg_init_one(&fc_req->sg_req, rspn_req, sizeof(*rspn_req));
-- 
2.34.1