linux-kernel - [PATCH] smb: avoid field overflow warning

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Message-Id: <20230616090749.2646749-1-arnd@kernel.org>
Date:   Fri, 16 Jun 2023 11:07:28 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Namjae Jeon <linkinjeon@...nel.org>,
        Steve French <sfrench@...ba.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Tom Talpey <tom@...pey.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Christian Brauner <brauner@...nel.org>,
        Dave Chinner <dchinner@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Mickaël Salaün <mic@...ikod.net>,
        Ronnie Sahlberg <lsahlber@...hat.com>,
        Hyunchul Lee <hyc.lee@...il.com>, linux-cifs@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: [PATCH] smb: avoid field overflow warning

From: Arnd Bergmann <arnd@...db.de>

clang warns about a possible field overflow in a memcpy:

In file included from fs/smb/server/smb_common.c:7:
include/linux/fortify-string.h:583:4: error: call to '__write_overflow_field' declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
                        __write_overflow_field(p_size_field, size);

It appears to interpret the "&out[baselen + 4]" as referring to a single
byte of the character array, while the equivalen "out + baselen + 4" is
seen as an offset into the array.

I don't see that kind of warning elsewhere, so just go with the simple
rework.

Fixes: e2f34481b24db ("cifsd: add server-side procedures for SMB3")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 fs/smb/server/smb_common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/smb/server/smb_common.c b/fs/smb/server/smb_common.c
index a7e81067bc991..e3273fa640b07 100644
--- a/fs/smb/server/smb_common.c
+++ b/fs/smb/server/smb_common.c
@@ -536,7 +536,7 @@ int ksmbd_extract_shortname(struct ksmbd_conn *conn, const char *longname,
 	out[baselen + 3] = PERIOD;
 
 	if (dot_present)
-		memcpy(&out[baselen + 4], extension, 4);
+		memcpy(out + baselen + 4, extension, 1);
 	else
 		out[baselen + 4] = '\0';
 	smbConvertToUTF16((__le16 *)shortname, out, PATH_MAX,
-- 
2.39.2