Hi, On 2021-06-29 06:48, Davis wrote: > Greetings! > > Could it be possible that > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v5.12.13&id=a8c4d76a8dd4fb9666fc8919a703d85fb8f44ed8 > or at least its backport to 4.4 has the potential for memory > corruption due to incorrect pointer calculation? > Shouldn't the line: > struct ethhdr *ehdr = (void *)skb_mac_header(skb); > be: > struct ethhdr *ehdr = (struct ethhdr *) skb->data; > > Later ehdr->h_dest is referenced, read and (when not equal to expected > value) written: > if (unlikely(skb->protocol == sdata->control_port_protocol && > !ether_addr_equal(ehdr->h_dest, sdata->vif.addr))) > ether_addr_copy(ehdr->h_dest, sdata->vif.addr); > > In my case after cherry-picking > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v4.4.273&id=e3d4030498c304d7c36bccc6acdedacf55402387 > to 4.4 kernel of an ARM device occasional memory corruption was observed. > > To investigate this issue logging was added - the pointer calculation > was expressed as: > struct ethhdr *ehdr = (void *)skb_mac_header(skb); > struct ethhdr *ehdr2 = (struct ethhdr *) skb->data; > and memory writing was replaced by logging: > if (unlikely(skb->protocol == sdata->control_port_protocol && > (!ether_addr_equal(ehdr->h_dest, sdata->vif.addr) || > !ether_addr_equal(ehdr2->h_dest, sdata->vif.addr)))) > printk(KERN_ERR "Matching1: %u, matching2: %u, addr1: %px, addr2: > %px", !ether_addr_equal(ehdr->h_dest, sdata->vif.addr), > !ether_addr_equal(ehdr2->h_dest, sdata->vif.addr), ehdr->h_dest, > ehdr2->h_dest); > > During normal use of wifi (in residential environment) logging was > triggered several times, in all cases matching1 was 1 and matching2 > was 0. > This makes me think that normal control frames were received and > correctly validated by !ether_addr_equal(ehdr2->h_dest, > sdata->vif.addr), however !ether_addr_equal(ehdr->h_dest, > sdata->vif.addr) was checking incorrect buffer and identified the > frames as malformed/correctable. > This also explains memory corruption - offset difference between both > buffers (addr1 and addr2) was close to 64 KB in all cases, virtually > always a random memory location (around 64 KB away from the correct > buffer) will belong to something else, will have a value that differs > from the expected MAC address and will get overwritten by the > cherry-picked code. It seems that the 4.4 backport is broken. The problem is the fact that skb_mac_header is called before eth_type_trans(). This means that the mac header offset still has the default value of (u16)-1, resulting in the 64 KB memory offset that you observed. I think that for 4.4, the code should be changed to use skb->data instead of skb_mac_header. 4.9 looks broken in the same way. 5.4 seems fine, so newer kernels should be fine as well. - Felix
