From 28f5df210d06beb5920cf80446f1c27456c14b92 Mon Sep 17 00:00:00 2001 From: Yann Droneaud Date: Sun, 25 Aug 2024 16:47:50 +0200 Subject: [PATCH] random: vDSO: reject unknown getrandom() flags Like the getrandom() syscall, vDSO getrandom() must also reject unknown flags. [1] It would be possible to return -EINVAL from vDSO itself, but in the possible case that a new flag is added to getrandom() syscall in the future, it would be easier to get the behavior from the syscall, instead of erroring until the vDSO is extended to support the new flag or explicitly falling back. [1] Designing the API: Planning for Extension https://docs.kernel.org/process/adding-syscalls.html#designing-the-api-planning-for-extension Signed-off-by: Yann Droneaud [Jason: reworded commit message] Signed-off-by: Jason A. Donenfeld --- lib/vdso/getrandom.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c index b230f0b10832..e1db228bc4f0 100644 --- a/lib/vdso/getrandom.c +++ b/lib/vdso/getrandom.c @@ -85,6 +85,10 @@ __cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_ if (unlikely(((unsigned long)opaque_state & ~PAGE_MASK) + sizeof(*state) > PAGE_SIZE)) return -EFAULT; + /* Handle unexpected flags by falling back to the kernel. */ + if (unlikely(flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))) + goto fallback_syscall; + /* If the caller passes the wrong size, which might happen due to CRIU, fallback. */ if (unlikely(opaque_len != sizeof(*state))) goto fallback_syscall;