CVE-2026-90065 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
net/smc: release the internal TCP sock on IPPROTO_SMC socket creation failure
IPPROTO_SMC sockets create an internal TCP sock ("clcsock") from the proto->init hook. When socket creation fails after proto->init has run - e.g. a cgroup BPF program attached to BPF_CGROUP_INET_SOCK_CREATE denies the socket - sk_common_release() only invokes sk_prot->destroy if it is set, but neither smc_inet_prot nor smc_inet6_prot defines it, and smc_destruct() returns early unless sk_state is SMC_CLOSED. As a result, every failing socket(AF_INET, SOCK_STREAM, IPPROTO_SMC) call leaks one tcp_sock, so an unprivileged task able to attach a deny-all BPF_CGROUP_INET_SOCK_CREATE program to its own cgroup can grow kernel memory unboundedly.
Add a .destroy hook to both protos that releases the clcsock via smc_clcsock_release(). smc_sk_init() hashes the sock into the smc hashinfo before the clcsock is created, and smc_diag dumps walk that hash dereferencing smc->clcsock without taking clcsock_release_lock, while sk_common_release() calls .destroy before .unhash. Unhash the sock before releasing the clcsock, as __smc_release() does, so a concurrent dump cannot observe the release; the second unhash in sk_common_release() is a no-op.
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel vulnerability identified involves a resource leak within the SMC (Shared Memory Communications) networking subsystem, specifically affecting IPPROTO_SMC socket creation failures. This flaw stems from an incomplete cleanup sequence when internal TCP sockets fail to initialize properly after their initial allocation hooks have executed. The core issue lies in how the kernel handles the lifecycle of these internal structures during error conditions, leading to unbounded memory consumption if exploited by a local user with appropriate cgroup permissions.
SMC technology allows applications to communicate using shared memory for data transfer while relying on TCP sockets for control signaling and connection management. When an application creates an IPPROTO_SMC socket, the kernel invokes the proto->init hook to allocate and initialize an internal TCP socket known as clcsock. This clcsock is essential for managing the SMC connection state. However, if subsequent steps in the socket creation process fail—for instance, due to a cgroup BPF program attached to BPF_CGROUP_INET_SOCK_CREATE denying the request—the cleanup logic fails to properly release this internal TCP structure. The standard release path relies on sk_common_release() invoking sk_prot->destroy when available. In the case of SMC protocols smc_inet_prot and smc_inet6_prot, no destroy hook was defined at the time of this vulnerability's existence. Furthermore, the destructor function smc_destruct() is designed to return early unless the socket state is explicitly marked as SMC_CLOSED. Since a failed creation does not reach this closed state, the internal tcp_sock remains allocated in kernel memory without being freed.
This oversight results in a significant resource leak where every failed attempt to create an IPPROTO_SMC socket leaves behind one unreleased tcp_sock structure. An unprivileged user can exploit this by attaching a deny-all BPF program to their cgroup for inet sock creation and repeatedly attempting to open SMC sockets. Each failure increments the kernel memory usage without bound, effectively creating a local denial-of-service condition that consumes system resources until stability is compromised or out-of-memory conditions are triggered. This aligns with CWE-401 (Missing Release of Memory after Effective Lifetime) as it involves failing to release allocated memory in error paths, and can be categorized under ATT&CK T1496 (Resource Hijacking) due to the potential for exhausting system resources through repeated exploitation attempts.
The resolution addresses this issue by introducing a .destroy hook to both smc_inet_prot and smc_inet6_prot structures. This new hook ensures that when socket release is initiated, the internal clcsock is properly released via the smc_clcsock_release() function, preventing further memory leaks. However, implementing this fix required careful attention to concurrency and race conditions inherent in the kernel's networking stack. The initialization sequence hashes the SMC sock into a global hashinfo before creating the clcsock, while diagnostic tools like smc_diag traverse this hash table and dereference the clcsock pointer without holding specific locks during their traversal.
To prevent use-after-free vulnerabilities or crashes resulting from concurrent access during cleanup, the fix modifies the release order within sk_common_release(). The sock is unhashed from the global list before the destroy hook attempts to release the clcsock. This ensures that any ongoing diagnostic dump operations will not observe a partially released structure. Although this results in a second unhash operation being performed by sk_common_release(), it acts as a no-op since the socket has already been removed, thereby maintaining consistency and safety without introducing additional complexity or performance penalties. This approach preserves data integrity while ensuring complete resource cleanup upon failure scenarios.