Commit 698eb826 authored Sep 21, 2023 by peterz@infradead.org Committed by Peter Zijlstra Sep 21, 2023

futex: Validate futex value against futex size



Ensure the futex value fits in the given futex size. Since this adds a
constraint to an existing syscall, it might possibly change behaviour.

Currently the value would be truncated to a u32 and any high bits
would get silently lost.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230921105247.828934099@noisy.programming.kicks-ass.net

parent 5694289c

kernel/futex/futex.h

+10 −0

Original line number	Diff line number	Diff line
		@@ -85,6 +85,16 @@ static inline bool futex_flags_valid(unsigned int flags)
		return true;
		}

		static inline bool futex_validate_input(unsigned int flags, u64 val)
		{
		int bits = 8 * futex_size(flags);

		if (bits < 64 && (val >> bits))
		return false;

		return true;
		}

		#ifdef CONFIG_FAIL_FUTEX
		extern bool should_fail_futex(bool fshared);
		#else

kernel/futex/syscalls.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -209,6 +209,9 @@ static int futex_parse_waitv(struct futex_vector *futexv,
		if (!futex_flags_valid(flags))
		return -EINVAL;

		if (!futex_validate_input(flags, aux.val))
		return -EINVAL;

		futexv[i].w.flags = flags;
		futexv[i].w.val = aux.val;
		futexv[i].w.uaddr = aux.uaddr;