[PATCH] fs/cifs: suppress a string overflow warning

[Steve French]

Merged into cifs-2.6.git for-next

Is the message annoying enough on powerpc to merit going into
4.19-rc3, presumably should wait for 4.20?
On Sun, Sep 2, 2018 at 10:24 PM Stephen Rothwell <sfr at canb.auug.org.au> wrote:
>
> A powerpc build of cifs with gcc v8.2.0 produces this warning:
>
> fs/cifs/cifssmb.c: In function ‘CIFSSMBNegotiate’:
> fs/cifs/cifssmb.c:605:3: warning: ‘strncpy’ writing 16 bytes into a region of size 1 overflows the destination [-Wstringop-overflow=]
>    strncpy(pSMB->DialectsArray+count, protocols[i].name, 16);
>    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Since we are already doing a strlen() on the source, change the strncpy
> to a memcpy().
>
> Signed-off-by: Stephen Rothwell <sfr at canb.auug.org.au>
> ---
>  fs/cifs/cifssmb.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
> index dc2f4cf08fe9..dcf939cb9d2f 100644
> --- a/fs/cifs/cifssmb.c
> +++ b/fs/cifs/cifssmb.c
> @@ -601,10 +601,14 @@ CIFSSMBNegotiate(const unsigned int xid, struct cifs_ses *ses)
>         }
>
>         count = 0;
> +       /*
> +        * We know that all the name entries in the protocols array
> +        * are short (< 16 bytes anyway) and are NUL terminated.
> +        */
>         for (i = 0; i < CIFS_NUM_PROT; i++) {
> -               strncpy(pSMB->DialectsArray+count, protocols[i].name, 16);
> -               count += strlen(protocols[i].name) + 1;
> -               /* null at end of source and target buffers anyway */
> +               size_t len = strlen(protocols[i].name) + 1;
> +               memcpy(pSMB->DialectsArray+count, protocols[i].name, len);
> +               count += len;
>         }
>         inc_rfc1001_len(pSMB, count);
>         pSMB->ByteCount = cpu_to_le16(count);
> --
> 2.19.0.rc1
>
> --
> Cheers,
> Stephen Rothwell



-- 
Thanks,

Steve