CVE-2025-21635: 
Linux Kernel vulnerability analysis and mitigation

CVE-2025-21635 is a vulnerability in the Linux kernel's RDS (Reliable Datagram Sockets) TCP implementation, discovered in January 2025. The vulnerability specifically affects the sysctl handling of RDS TCP receive and send buffer settings. The issue stems from improper usage of the current->nsproxy structure in the network namespace handling (NVD).

The vulnerability arises from using the 'net' structure via 'current->nsproxy' in the RDS TCP sysctl handlers, which is problematic for two main reasons: inconsistency in getting information from reader's/writer's netns versus opener's netns, and potential null pointer dereference when current->nsproxy is NULL during task exit. The issue was identified in the rdstcpskbuf_handler function within the Linux kernel's RDS TCP implementation (Kernel Commit).

When exploited, this vulnerability can lead to a kernel 'Oops' (null-ptr-deref) condition, particularly when the current task is exiting. This can potentially cause system instability or denial of service in affected Linux systems (Kernel Commit).

A fix has been implemented that modifies the RDS TCP sysctl handlers to avoid using current->nsproxy. Instead, the per-netns structure is obtained from the table->data using container_of(), and the 'net' structure is retrieved from the listen socket when available. This patch has been merged into the Linux kernel (Kernel Commit).