[PATVH,v2] net: ne2000: fix bounds check in ioport operations

From: Prasad J Pandit <pjp@fedoraproject.org>

While doing ioport r/w operations, ne2000 device emulation suffers
from OOB r/w errors. Update respective array bounds check to avoid
OOB access.

Reported-by: Ling Liu <liuling-it@360.cn>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 hw/net/ne2000.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

Updated as per review in
  -> https://lists.gnu.org/archive/html/qemu-devel/2015-12/msg04856.html

On 12/31/2015 12:53 PM, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
>
> While doing ioport r/w operations, ne2000 device emulation suffers
> from OOB r/w errors. Update respective array bounds check to avoid
> OOB access.
>
> Reported-by: Ling Liu <liuling-it@360.cn>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  hw/net/ne2000.c | 28 +++++++++++++++-------------
>  1 file changed, 15 insertions(+), 13 deletions(-)
>
> Updated as per review in
>   -> https://lists.gnu.org/archive/html/qemu-devel/2015-12/msg04856.html
>
> diff --git a/hw/net/ne2000.c b/hw/net/ne2000.c
> index 010f9ef..d1f764b 100644
> --- a/hw/net/ne2000.c
> +++ b/hw/net/ne2000.c
> @@ -447,8 +447,7 @@ static uint32_t ne2000_ioport_read(void *opaque, uint32_t addr)
>  static inline void ne2000_mem_writeb(NE2000State *s, uint32_t addr,
>                                       uint32_t val)
>  {
> -    if (addr < 32 ||
> -        (addr >= NE2000_PMEM_START && addr < NE2000_MEM_SIZE)) {
> +    if (addr < 32 || (addr >= NE2000_PMEM_START && addr < NE2000_MEM_SIZE)) {

The change is unnecessary.

>          s->mem[addr] = val;
>      }
>  }
> @@ -457,9 +456,10 @@ static inline void ne2000_mem_writew(NE2000State *s, uint32_t addr,
>                                       uint32_t val)
>  {
>      addr &= ~1; /* XXX: check exact behaviour if not even */
> -    if (addr < 32 ||
> -        (addr >= NE2000_PMEM_START && addr < NE2000_MEM_SIZE)) {
> -        *(uint16_t *)(s->mem + addr) = cpu_to_le16(val);
> +    if (addr < 32
> +        || (addr >= NE2000_PMEM_START
> +            && addr + sizeof(uint16_t) < NE2000_MEM_SIZE)) {

I think you mean '<=' instead of '<' here? (And for the other checks below).

> +        *(uint16_t *)(s->mem + addr) = cpu_to_le16(data);
>      }
>  }
>  
> @@ -467,16 +467,16 @@ static inline void ne2000_mem_writel(NE2000State *s, uint32_t addr,
>                                       uint32_t val)
>  {
>      addr &= ~1; /* XXX: check exact behaviour if not even */
> -    if (addr < 32 ||
> -        (addr >= NE2000_PMEM_START && addr < NE2000_MEM_SIZE)) {
> +    if (addr < 32
> +        || (addr >= NE2000_PMEM_START
> +            && addr + sizeof(uint32_t) < NE2000_MEM_SIZE)) {
>          stl_le_p(s->mem + addr, val);
>      }
>  }
>  
>  static inline uint32_t ne2000_mem_readb(NE2000State *s, uint32_t addr)
>  {
> -    if (addr < 32 ||
> -        (addr >= NE2000_PMEM_START && addr < NE2000_MEM_SIZE)) {
> +    if (addr < 32 || (addr >= NE2000_PMEM_START && addr < NE2000_MEM_SIZE)) {
>          return s->mem[addr];
>      } else {
>          return 0xff;
> @@ -486,8 +486,9 @@ static inline uint32_t ne2000_mem_readb(NE2000State *s, uint32_t addr)
>  static inline uint32_t ne2000_mem_readw(NE2000State *s, uint32_t addr)
>  {
>      addr &= ~1; /* XXX: check exact behaviour if not even */
> -    if (addr < 32 ||
> -        (addr >= NE2000_PMEM_START && addr < NE2000_MEM_SIZE)) {
> +    if (addr < 32
> +        || (addr >= NE2000_PMEM_START
> +            && addr + sizeof(uint16_t) < NE2000_MEM_SIZE)) {
>          return le16_to_cpu(*(uint16_t *)(s->mem + addr));
>      } else {
>          return 0xffff;
> @@ -497,8 +498,9 @@ static inline uint32_t ne2000_mem_readw(NE2000State *s, uint32_t addr)
>  static inline uint32_t ne2000_mem_readl(NE2000State *s, uint32_t addr)
>  {
>      addr &= ~1; /* XXX: check exact behaviour if not even */
> -    if (addr < 32 ||
> -        (addr >= NE2000_PMEM_START && addr < NE2000_MEM_SIZE)) {
> +    if (addr < 32
> +        || (addr >= NE2000_PMEM_START
> +            && addr + sizeof(uint32_t) < NE2000_MEM_SIZE)) {
>          return ldl_le_p(s->mem + addr);
>      } else {
>          return 0xffffffff;

+-- On Thu, 31 Dec 2015, Jason Wang wrote --+
| > -        (addr >= NE2000_PMEM_START && addr < NE2000_MEM_SIZE)) {
| > +    if (addr < 32 || (addr >= NE2000_PMEM_START && addr < NE2000_MEM_SIZE)) {
| 
| The change is unnecessary.

  Okay.
 
| > +    if (addr < 32
| > +        || (addr >= NE2000_PMEM_START
| > +            && addr + sizeof(uint16_t) < NE2000_MEM_SIZE)) {
| 
| I think you mean '<=' instead of '<' here? (And for the other checks below).

  I think <= would lead to an off-by-one, no? As the last array index would be 
one less than the size; Same as ne2000_mem_readb() above.

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F

On 12/31/2015 01:56 PM, P J P wrote:
> +-- On Thu, 31 Dec 2015, Jason Wang wrote --+
> | > -        (addr >= NE2000_PMEM_START && addr < NE2000_MEM_SIZE)) {
> | > +    if (addr < 32 || (addr >= NE2000_PMEM_START && addr < NE2000_MEM_SIZE)) {
> | 
> | The change is unnecessary.
>
>   Okay.
>  
> | > +    if (addr < 32
> | > +        || (addr >= NE2000_PMEM_START
> | > +            && addr + sizeof(uint16_t) < NE2000_MEM_SIZE)) {
> | 
> | I think you mean '<=' instead of '<' here? (And for the other checks below).
>
>   I think <= would lead to an off-by-one, no?

The real byte we could touch is in fact addr + sizeof(uint16_t) -1 here.

Consider we should allow double bytes access at NE2000_MEM_SIZE - 2, but
this patch forbids this.

Btw, looking at ne2000_mem_writew(), it has:

addr &= ~1;

at the beginning, so looks like we are really safe,  Need only to care
about writel?

>  As the last array index would be 
> one less than the size; Same as ne2000_mem_readb() above.
>
> Thank you.
> --
> Prasad J Pandit / Red Hat Product Security Team
> 47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F

+-- On Thu, 31 Dec 2015, Jason Wang wrote --+
| Btw, looking at ne2000_mem_writew(), it has:
| addr &= ~1;

  Yes, this seems to ensure that write starts at an even address.

| at the beginning, so looks like we are really safe,  Need only to care
| about writel?

  Right, I've sent an updated patch for the same.

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F