2023-07-21 11:10:14

by Peter Zijlstra

Subject: [PATCH v1 04/14] 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) <[email protected]>
---
kernel/futex/futex.h | 8 ++++++++
kernel/futex/syscalls.c | 3 +++
2 files changed, 11 insertions(+)

--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -86,6 +86,14 @@ static inline unsigned int futex_size(un
return 1 << size; /* {0,1,2,3} -> {1,2,4,8} */
}

+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
--- a/kernel/futex/syscalls.c
+++ b/kernel/futex/syscalls.c
@@ -209,6 +209,9 @@ static int futex_parse_waitv(struct fute
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;

2023-07-31 18:15:30

by Thomas Gleixner

Subject: Re: [PATCH v1 04/14] futex: Validate futex value against futex size

On Fri, Jul 21 2023 at 12:22, Peter Zijlstra wrote:
> +static inline bool futex_validate_input(unsigned int flags, u64 val)
> +{
> + int bits = 8 * futex_size(flags);
> + if (bits < 64 && (val >> bits))

New line between declaration and code.

> + return false;
> + return true;
> +}

Other than that::

Reviewed-by: Thomas Gleixner <[email protected]>