CVE-2023-52889: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-52889 is a vulnerability in the Linux kernel's AppArmor security module that can lead to a null pointer dereference. The issue occurs when receiving ICMP packets with secmark set while an ICMP raw socket is being created. The vulnerability was discovered in 2023 and affects various Linux kernel versions (Kernel Git).

The vulnerability occurs because SKCTX(sk)->label is updated in apparmorsocketpostcreate(), but packets can be delivered to the socket before that operation completes, causing a null pointer dereference. This specifically happens when receiving ICMP packets with secmark set during the ICMP raw socket creation process. The issue was introduced by commit ab9f2115081a which added secmark policy filtering capabilities to AppArmor (Kernel Git).

When exploited, this vulnerability can cause a kernel panic due to the null pointer dereference, potentially leading to system crashes and denial of service conditions. The issue manifests as a supervisor read access error in kernel mode, resulting in a system crash with a BUG message indicating kernel NULL pointer dereference (Kernel Git).

The issue has been fixed by adding a check for null label context and dropping packets in such cases. The fix was implemented by adding a condition to check if ctx->label is null before proceeding with secmark checks. If the label is null, the packet is dropped with -EACCES return code (Kernel Git).