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

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Message-ID: <CAKYAXd-j6mJ91hZUZi86HnGJahekHHgYz4ngWfF81QmYigGqVw@mail.gmail.com>
Date:   Fri, 16 Jun 2023 23:40:04 +0900
From:   Namjae Jeon <linkinjeon@...nel.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Steve French <sfrench@...ba.org>, 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: Re: [PATCH] smb: avoid field overflow warning

2023-06-16 18:07 GMT+09:00, Arnd Bergmann <arnd@...nel.org>:
> From: Arnd Bergmann <arnd@...db.de>
Hi Arnd,

>
> 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);
Is there any reason to change copy bytes from 4 bytes to 1 byte?

Thanks!
>  	else
>  		out[baselen + 4] = '\0';
>  	smbConvertToUTF16((__le16 *)shortname, out, PATH_MAX,
> --
> 2.39.2
>
>