Re: [PATCH 4/5] smb: client: Clear sensitive stack data in smb1encrypt.c

On Wed, Aug 12, 2026 at 10:13 PM Thomas Huth <[email protected]> wrote:
>
> From: Thomas Huth <[email protected]>
>
> Make sure to not leak signature data via the stack, clear it
> with memzero_explicit() before leaving the function.
>
> To avoid that we have to introduce "goto"-cleanup here, we re-arrange
> the code a little bit (and drop the commented cifs_dump_mem debug
> code that looks like a leftover from very early days).
>
> Signed-off-by: Thomas Huth <[email protected]>
> ---
>  fs/smb/client/smb1encrypt.c | 19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
>
> diff --git a/fs/smb/client/smb1encrypt.c b/fs/smb/client/smb1encrypt.c
> index bf10fdeeedcab..c9eb68f04e7b0 100644
> --- a/fs/smb/client/smb1encrypt.c
> +++ b/fs/smb/client/smb1encrypt.c
> @@ -81,6 +81,7 @@ int cifs_sign_rqst(struct smb_rqst *rqst, struct TCP_Server_Info *server,
>         else
>                 memcpy(cifs_pdu->Signature.SecuritySignature, smb_signature, 8);
>
> +       memzero_explicit(smb_signature, sizeof(smb_signature));
>         return rc;
>  }
>
> @@ -126,15 +127,13 @@ int cifs_verify_signature(struct smb_rqst *rqst,
>         rc = cifs_calc_signature(rqst, server, what_we_think_sig_should_be);
>         cifs_server_unlock(server);
The MD5 context in  cifs_calc_signature()  may remain uncleared when
__cifs_calc_signature()  fails.

rc = __cifs_calc_signature(...);
                                               ┃
memzero_explicit(&ctx, sizeof(ctx));