[PATCH][V2][cifs-next] cifs: fix dereference on ses before it is null checked

[Steve French]

Tentatively merged into cifs-2.6.git pending additional testing

Kicked off buildbot with rc7+patches in cifs for-next

See http://smb3-test-rhel-75.southcentralus.cloudapp.azure.com/#/builders/2/builds/247

On Mon, Sep 2, 2019 at 10:33 AM Colin King <colin.king at canonical.com> wrote:
>
> From: Colin Ian King <colin.king at canonical.com>
>
> The assignment of pointer server dereferences pointer ses, however,
> this dereference occurs before ses is null checked and hence we
> have a potential null pointer dereference.  Fix this by only
> dereferencing ses after it has been null checked.
>
> Addresses-Coverity: ("Dereference before null check")
> Fixes: 2808c6639104 ("cifs: add new debugging macro cifs_server_dbg")
> Signed-off-by: Colin Ian King <colin.king at canonical.com>
> ---
>  fs/cifs/smb2pdu.c   | 11 ++++++++---
>  fs/cifs/transport.c |  3 ++-
>  2 files changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
> index dbc6ef50dd45..0e92983de0b7 100644
> --- a/fs/cifs/smb2pdu.c
> +++ b/fs/cifs/smb2pdu.c
> @@ -2759,8 +2759,10 @@ SMB2_ioctl(const unsigned int xid, struct cifs_tcon *tcon, u64 persistent_fid,
>         else
>                 return -EIO;
>
> +       if (!ses)
> +               return -EIO;
>         server = ses->server;
> -       if (!ses || !(server))
> +       if (!server)
>                 return -EIO;
>
>         if (smb3_encryption_required(tcon))
> @@ -3058,13 +3060,16 @@ query_info(const unsigned int xid, struct cifs_tcon *tcon,
>         int rc = 0;
>         int resp_buftype = CIFS_NO_BUFFER;
>         struct cifs_ses *ses = tcon->ses;
> -       struct TCP_Server_Info *server = ses->server;
> +       struct TCP_Server_Info *server;
>         int flags = 0;
>         bool allocated = false;
>
>         cifs_dbg(FYI, "Query Info\n");
>
> -       if (!ses || !(server))
> +       if (!ses)
> +               return -EIO;
> +       server = ses->server;
> +       if (!server)
>                 return -EIO;
>
>         if (smb3_encryption_required(tcon))
> diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
> index 0d60bd2f4dca..a90bd4d75b4d 100644
> --- a/fs/cifs/transport.c
> +++ b/fs/cifs/transport.c
> @@ -1242,12 +1242,13 @@ SendReceive(const unsigned int xid, struct cifs_ses *ses,
>         struct kvec iov = { .iov_base = in_buf, .iov_len = len };
>         struct smb_rqst rqst = { .rq_iov = &iov, .rq_nvec = 1 };
>         struct cifs_credits credits = { .value = 1, .instance = 0 };
> -       struct TCP_Server_Info *server = ses->server;
> +       struct TCP_Server_Info *server;
>
>         if (ses == NULL) {
>                 cifs_dbg(VFS, "Null smb session\n");
>                 return -EIO;
>         }
> +       server = ses->server;
>         if (server == NULL) {
>                 cifs_dbg(VFS, "Null tcp session\n");
>                 return -EIO;
> --
> 2.20.1
>


-- 
Thanks,

Steve