Re: [Qemu-devel] [PATCH] e1000: cleanup process_tx_desc

[Jesse Larrew <jlarrew@linux.vnet.ibm.com>]

On 06/03/2013 10:20 AM, Andrew Jones wrote:
> Coverity complains about two overruns in process_tx_desc(). The
> complaints are false positives, but we might as well eliminate
> them. The problem is that "hdr" is defined as an unsigned int,
> but then used to offset an array of size 65536, and another of
> size 256 bytes. hdr will actually never be greater than 255
> though, as it's assigned only once and to the value of
> tp->hdr_len, which is an uint8_t. This patch simply gets rid of
> hdr, replacing it with tp->hdr_len, which makes it consistent
> with all other tp member use in the function.
> 
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> ---
>  hw/net/e1000.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 

The logic looks sound, but checkpatch detects some style issues. See below.

> diff --git a/hw/net/e1000.c b/hw/net/e1000.c
> index e6f46f0c511e8..eec3e7a4524d1 100644
> --- a/hw/net/e1000.c
> +++ b/hw/net/e1000.c
> @@ -556,7 +556,7 @@ process_tx_desc(E1000State *s, struct e1000_tx_desc *dp)
>      uint32_t txd_lower = le32_to_cpu(dp->lower.data);
>      uint32_t dtype = txd_lower & (E1000_TXD_CMD_DEXT | E1000_TXD_DTYP_D);
>      unsigned int split_size = txd_lower & 0xffff, bytes, sz, op;
> -    unsigned int msh = 0xfffff, hdr = 0;
> +    unsigned int msh = 0xfffff;
>      uint64_t addr;
>      struct e1000_context_desc *xp = (struct e1000_context_desc *)dp;
>      struct e1000_tx *tp = &s->tx;
> @@ -603,8 +603,7 @@ process_tx_desc(E1000State *s, struct e1000_tx_desc *dp)
>          
>      addr = le64_to_cpu(dp->buffer_addr);
>      if (tp->tse && tp->cptse) {
> -        hdr = tp->hdr_len;
> -        msh = hdr + tp->mss;
> +        msh = tp->hdr_len + tp->mss;
>          do {
>              bytes = split_size;
>              if (tp->size + bytes > msh)
> @@ -612,14 +611,15 @@ process_tx_desc(E1000State *s, struct e1000_tx_desc *dp)
> 
>              bytes = MIN(sizeof(tp->data) - tp->size, bytes);
>              pci_dma_read(&s->dev, addr, tp->data + tp->size, bytes);
> -            if ((sz = tp->size + bytes) >= hdr && tp->size < hdr)
> -                memmove(tp->header, tp->data, hdr);
> +            if ((sz = tp->size + bytes) >= tp->hdr_len
> +                && tp->size < tp->hdr_len)
> +                memmove(tp->header, tp->data, tp->hdr_len);

The 'if' statement above needs some braces. Checkpatch also isn't wild about
the assignment inside of the conditional.

>              tp->size = sz;
>              addr += bytes;
>              if (sz == msh) {
>                  xmit_seg(s);
> -                memmove(tp->data, tp->header, hdr);
> -                tp->size = hdr;
> +                memmove(tp->data, tp->header, tp->hdr_len);
> +                tp->size = tp->hdr_len;
>              }
>          } while (split_size -= bytes);
>      } else if (!tp->tse && tp->cptse) {
> @@ -633,7 +633,7 @@ process_tx_desc(E1000State *s, struct e1000_tx_desc *dp)
> 
>      if (!(txd_lower & E1000_TXD_CMD_EOP))
>          return;
> -    if (!(tp->tse && tp->cptse && tp->size < hdr))
> +    if (!(tp->tse && tp->cptse && tp->size < tp->hdr_len))
>          xmit_seg(s);

Braces here as well.

>      tp->tso_frames = 0;
>      tp->sum_needed = 0;
> 

Although the style issues were present to begin with, we may as well take
the opportunity to fix them.

Sincerely,

Jesse Larrew
Software Engineer, KVM Team
IBM Linux Technology Center
Phone: (512) 973-2052 (T/L: 363-2052)
jlarrew@linux.vnet.ibm.com