Linux kernel algif_aead: minimum receive-buffer check ignores the authentication tag during decryption

Impact

The AF_ALG AEAD interface validated the minimum size of the caller-supplied receive buffer without accounting for the authentication tag length on the decryption path, so a decrypt request could be accepted with a destination buffer smaller than the data the kernel is about to write there. The record categorises the outcome as loss of availability - a local user driving the kernel crypto userspace API can push the AEAD path into an undersized-buffer condition. On a shared GPU node the cost is the usual one for a kernel-side fault: one unprivileged tenant process destabilises a host carrying other tenants' jobs, and recovery is a reboot rather than a container restart. Like the rest of AF_ALG this surface is reachable from inside containers unless the socket family is explicitly denied.

Who can reach it

Local, authenticated: any unprivileged user or container process able to create an AF_ALG socket, bind an AEAD algorithm, and issue a decrypt recvmsg() with a short buffer. No capability or device access needed.

What to do

Move to a stable kernel that includes the algif_aead minimum-RX-size fix and reboot the affected nodes; there is no runtime toggle for the check. Bundle it with the other AF_ALG kernel fixes in the same maintenance window rather than rebooting twice. Where tenant workloads have no reason to use the kernel crypto userspace API, denying AF_ALG socket creation via seccomp removes the surface without waiting for the reboot.

References

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