Wind River Support Network

Description

In the Linux kernel, the following vulnerability has been resolved:  net: stmmac: fix integer underflow in chain mode  The jumbo_frm() chain-mode implementation unconditionally computes      len = nopaged_len - bmax;  where nopaged_len = skb_headlen(skb) (linear bytes only) and bmax is BUF_SIZE_8KiB or BUF_SIZE_2KiB.  However, the caller stmmac_xmit() decides to invoke jumbo_frm() based on skb->len (total length including page fragments):      is_jumbo = stmmac_is_jumbo_frm(priv, skb->len, enh_desc);  When a packet has a small linear portion (nopaged_len <= bmax) but a large total length due to page fragments (skb->len > bmax), the subtraction wraps as an unsigned integer, producing a huge len value (~0xFFFFxxxx).  This causes the while (len != 0) loop to execute hundreds of thousands of iterations, passing skb->data + bmax * i pointers far beyond the skb buffer to dma_map_single().  On IOMMU-less SoCs (the typical deployment for stmmac), this maps arbitrary kernel memory to the DMA engine, constituting a kernel memory disclosure and potential memory corruption from hardware.  Fix this by introducing a buf_len local variable clamped to min(nopaged_len, bmax).  Computing len = nopaged_len - buf_len is then always safe: it is zero when the linear portion fits within a single descriptor, causing the while (len != 0) loop to be skipped naturally, and the fragment loop in stmmac_xmit() handles page fragments afterward.