Wind River Support Network

Description

In the Linux kernel, the following vulnerability has been resolved:  ipv4: raw: reject IP_HDRINCL packets with ihl < 5  raw_send_hdrinc() validates that the caller-supplied IPv4 header fits within the message length:      iphlen = iph->ihl * 4;     err = -EINVAL;     if (iphlen > length)         goto error_free;      if (iphlen >= sizeof(*iph)) {         /* fix up saddr, tot_len, id, csum, transport_header */     }  It does not, however, reject ihl < 5.  For such a packet the "if (iphlen >= sizeof(*iph))" branch is skipped, leaving the crafted iphdr untouched, but the packet is still handed to __ip_local_out() and onward.  Downstream consumers that read iph->ihl assume a sane value: net/ipv4/ah4.c:ah_output() in particular subtracts sizeof(struct iphdr) from top_iph->ihl * 4 and passes the (signed-int-negative, then cast to size_t) result to memcpy(), producing an OOB access of length close to SIZE_MAX and a host kernel panic.  An IPv4 header with ihl < 5 is malformed by definition (RFC 791: "Internet Header Length is the length of the internet header in 32 bit words ... Note that the minimum value for a correct header is 5.").  The kernel should not be willing to inject such a packet into its own output path.  Reject "iphlen < sizeof(*iph)" alongside the existing "iphlen > length" check.  This matches the principle that locally constructed packets that re-enter the IP stack must pass the same basic sanity tests that a foreign packet would be subjected to.  Once this lands, the "if (iphlen >= sizeof(*iph))" wrapper around the fixup branch becomes redundant; left in place to keep the patch minimal and backport-friendly.  A follow-up can unwrap it.  Note that commit 86f4c90a1c5c ("ipv4, ipv6: ensure raw socket message is big enough to hold an IP header") ensures the message buffer is large enough to hold an iphdr, but does not constrain the self-reported iph->ihl.  Reachability: the malformed packet source is any caller with CAP_NET_RAW, including an unprivileged process in a user+net namespace on a kernel with CONFIG_USER_NS=y.  The reproduced AH crash also requires a matching xfrm AH policy on the outgoing route; a container granted CAP_NET_ADMIN can install that state and policy in its netns.  Loopback bypasses xfrm_output, so the trigger uses a real netdev.  Reproduced on UML + KASAN: kernel-mode fault at addr 0x0 with memcpy_orig at the crash site.  Same shape reproduces inside a rootless Docker container with --cap-add NET_ADMIN on a stock distro kernel.