Re: [Qemu-devel] [PATCH] contrib/rdmacm-mux: Fix out-of-bounds risk

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 2/12/19 12:23 PM, Yuval Shaia wrote:
> The function get_fd extract context from the received MAD message and
> uses it as a key to fetch the destination fd from the mapping table.
> A context can be dgid in case of CM request message or comm_id in case
> of CM SIDR response message.
> 
> When MAD message with a smaller size as expected for the message type
> received we are hitting out-of-bounds where we are looking for the
> context out of message boundaries.
> 
> Fix it by validating the message size.
> 

Cc: qemu-stable@nongnu.org

> Reported-by Sam Smith <sam.j.smith@oracle.com>
> Signed-off-by: Yuval Shaia <yuval.shaia@oracle.com>

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

> ---
>  contrib/rdmacm-mux/main.c | 35 +++++++++++++++++++++++++++++++++--
>  1 file changed, 33 insertions(+), 2 deletions(-)
> 
> diff --git a/contrib/rdmacm-mux/main.c b/contrib/rdmacm-mux/main.c
> index ae88c77a1e..21cc804367 100644
> --- a/contrib/rdmacm-mux/main.c
> +++ b/contrib/rdmacm-mux/main.c
> @@ -300,7 +300,7 @@ static void hash_tbl_remove_fd_ifid_pair(int fd)
>      pthread_rwlock_unlock(&server.lock);
>  }
>  
> -static int get_fd(const char *mad, int *fd, __be64 *gid_ifid)
> +static int get_fd(const char *mad, int umad_len, int *fd, __be64 *gid_ifid)
>  {
>      struct umad_hdr *hdr = (struct umad_hdr *)mad;
>      char *data = (char *)hdr + sizeof(*hdr);
> @@ -308,13 +308,35 @@ static int get_fd(const char *mad, int *fd, __be64 *gid_ifid)
>      uint16_t attr_id = be16toh(hdr->attr_id);
>      int rc = 0;
>  
> +    if (umad_len <= sizeof(*hdr)) {
> +        rc = -EINVAL;
> +        syslog(LOG_DEBUG, "Ignoring MAD packets with header only\n");
> +        goto out;
> +    }
> +
>      switch (attr_id) {
>      case UMAD_CM_ATTR_REQ:
> +        if (unlikely(umad_len < sizeof(*hdr) + CM_REQ_DGID_POS +
> +            sizeof(*gid_ifid))) {
> +            rc = -EINVAL;
> +            syslog(LOG_WARNING,
> +                   "Invalid MAD packet size (%d) for attr_id 0x%x\n", umad_len,
> +                    attr_id);
> +            goto out;
> +        }
>          memcpy(gid_ifid, data + CM_REQ_DGID_POS, sizeof(*gid_ifid));
>          rc = hash_tbl_search_fd_by_ifid(fd, gid_ifid);
>          break;
>  
>      case UMAD_CM_ATTR_SIDR_REQ:
> +        if (unlikely(umad_len < sizeof(*hdr) + CM_SIDR_REQ_DGID_POS +
> +            sizeof(*gid_ifid))) {
> +            rc = -EINVAL;
> +            syslog(LOG_WARNING,
> +                   "Invalid MAD packet size (%d) for attr_id 0x%x\n", umad_len,
> +                    attr_id);
> +            goto out;
> +        }
>          memcpy(gid_ifid, data + CM_SIDR_REQ_DGID_POS, sizeof(*gid_ifid));
>          rc = hash_tbl_search_fd_by_ifid(fd, gid_ifid);
>          break;
> @@ -331,6 +353,13 @@ static int get_fd(const char *mad, int *fd, __be64 *gid_ifid)
>          data += sizeof(comm_id);
>          /* Fall through */
>      case UMAD_CM_ATTR_SIDR_REP:
> +        if (unlikely(umad_len < sizeof(*hdr) + sizeof(comm_id))) {
> +            rc = -EINVAL;
> +            syslog(LOG_WARNING,
> +                   "Invalid MAD packet size (%d) for attr_id 0x%x\n", umad_len,
> +                   attr_id);
> +            goto out;
> +        }
>          memcpy(&comm_id, data, sizeof(comm_id));
>          if (comm_id) {
>              rc = hash_tbl_search_fd_by_comm_id(comm_id, fd, gid_ifid);
> @@ -344,6 +373,7 @@ static int get_fd(const char *mad, int *fd, __be64 *gid_ifid)
>  
>      syslog(LOG_DEBUG, "mad_to_vm: %d 0x%x 0x%x\n", *fd, attr_id, comm_id);
>  
> +out:
>      return rc;
>  }
>  
> @@ -372,7 +402,8 @@ static void *umad_recv_thread_func(void *args)
>          } while (rc && server.run);
>  
>          if (server.run) {
> -            rc = get_fd(msg.umad.mad, &fd, &msg.hdr.sgid.global.interface_id);
> +            rc = get_fd(msg.umad.mad, msg.umad_len, &fd,
> +                        &msg.hdr.sgid.global.interface_id);
>              if (rc) {
>                  continue;
>              }
>