Re: [Qemu-devel] [PATCH v3 3/4] ivshmem: Fix potential OOB r/w access

[Michael S. Tsirkin]

On Mon, Sep 15, 2014 at 06:40:07PM +0200, Andreas Färber wrote:
> From: Sebastian Krahmer <address@hidden>
> 
> Fix OOB access via malformed incoming_posn parameters
> and check that requested memory is actually alloc'ed.
> 
> Signed-off-by: Sebastian Krahmer <address@hidden>
> [AF: Rebased, cleanups, avoid fd leak]
> Cc: address@hidden
> Signed-off-by: Andreas Färber <address@hidden>

Reviewed-by: Michael S. Tsirkin <address@hidden>

> ---
>  hw/misc/ivshmem.c | 27 +++++++++++++++++++++++----
>  1 file changed, 23 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
> index 24f74f6..ecef82a 100644
> --- a/hw/misc/ivshmem.c
> +++ b/hw/misc/ivshmem.c
> @@ -29,6 +29,7 @@
>  
>  #include <sys/mman.h>
>  #include <sys/types.h>
> +#include <limits.h>
>  
>  #define PCI_VENDOR_ID_IVSHMEM   PCI_VENDOR_ID_REDHAT_QUMRANET
>  #define PCI_DEVICE_ID_IVSHMEM   0x1110
> @@ -410,14 +411,24 @@ static void close_guest_eventfds(IVShmemState *s, int 
> posn)
>  
>  /* this function increase the dynamic storage need to store data about other
>   * guests */
> -static void increase_dynamic_storage(IVShmemState *s, int new_min_size) {
> +static int increase_dynamic_storage(IVShmemState *s, int new_min_size)
> +{
>  
>      int j, old_nb_alloc;
>  
> +    /* check for integer overflow */
> +    if (new_min_size >= INT_MAX / sizeof(Peer) - 1 || new_min_size <= 0) {
> +        return -1;
> +    }
> +
>      old_nb_alloc = s->nb_peers;
>  
> -    while (new_min_size >= s->nb_peers)
> -        s->nb_peers = s->nb_peers * 2;
> +    if (new_min_size >= s->nb_peers) {
> +        /* +1 because #new_min_size is used as last array index */
> +        s->nb_peers = new_min_size + 1;
> +    } else {
> +        return 0;
> +    }
>  
>      IVSHMEM_DPRINTF("bumping storage to %d guests\n", s->nb_peers);
>      s->peers = g_realloc(s->peers, s->nb_peers * sizeof(Peer));
> @@ -427,6 +438,8 @@ static void increase_dynamic_storage(IVShmemState *s, int 
> new_min_size) {
>          s->peers[j].eventfds = NULL;
>          s->peers[j].nb_eventfds = 0;
>      }
> +
> +    return 0;
>  }
>  
>  static void ivshmem_read(void *opaque, const uint8_t *buf, int size)
> @@ -469,7 +482,13 @@ static void ivshmem_read(void *opaque, const uint8_t 
> *buf, int size)
>  
>      /* make sure we have enough space for this guest */
>      if (incoming_posn >= s->nb_peers) {
> -        increase_dynamic_storage(s, incoming_posn);
> +        if (increase_dynamic_storage(s, incoming_posn) < 0) {
> +            error_report("increase_dynamic_storage() failed");
> +            if (tmp_fd != -1) {
> +                close(tmp_fd);
> +            }
> +            return;
> +        }
>      }
>  
>      if (tmp_fd == -1) {
> -- 
> 1.8.4.5