On 2021-06-30 at 21:01 Felix Fietkau (<nbd@xxxxxxxx>) wrote: > > On 2021-06-29 19:49, Greg Kroah-Hartman wrote: > > On Tue, Jun 29, 2021 at 07:26:03PM +0200, Felix Fietkau wrote: > >> > >> 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. > > > > Thanks for looking into this, can you submit a patch to fix this up in > > the older kernel trees? > Sorry, I don't have time to prepare and test the patches at the moment. > > - Felix If testing procedure mentioned in my first email is sufficient (and using skb->data is the correct solution in kernel trees where current code doesn't work properly), I can make and test the patches. Should I do that? Br, Davis
