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

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

[Stephen Rothwell]

[-- Attachment #1: Type: text/plain, Size: 1480 bytes --]

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@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

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

Re: [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@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@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

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

[Stephen Rothwell]

[-- Attachment #1: Type: text/plain, Size: 319 bytes --]

Hi Steve,

On Mon, 3 Sep 2018 09:44:17 -0500 Steve French <smfrench@gmail.com> wrote:
>
> 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?

Up to you, but 4.20 is probably fine.

-- 
Cheers,
Stephen Rothwell

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

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

[Steve French]

ok - it looks like it will be a little simpler if I wait
On Mon, Sep 3, 2018 at 8:22 PM Stephen Rothwell <sfr@canb.auug.org.au> wrote:
>
> Hi Steve,
>
> On Mon, 3 Sep 2018 09:44:17 -0500 Steve French <smfrench@gmail.com> wrote:
> >
> > 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?
>
> Up to you, but 4.20 is probably fine.
>
> --
> Cheers,
> Stephen Rothwell



-- 
Thanks,

Steve