[PATCH v3 04/15] futex: Validate futex value against futex size

peterz
2023-09-21T20:21:46Z

[-- Attachment #1: peterz-futex2-enforce-bits.patch --]
[-- Type: text/plain, Size: 1460 bytes --]

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>
---
kernel/futex/futex.h | 10 ++++++++++
kernel/futex/syscalls.c | 3 +++
2 files changed, 13 insertions(+)

Index: linux-2.6/kernel/futex/futex.h
===================================================================
--- linux-2.6.orig/kernel/futex/futex.h
+++ linux-2.6/kernel/futex/futex.h
@@ -85,6 +85,16 @@ static inline bool futex_flags_valid(uns
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
Index: linux-2.6/kernel/futex/syscalls.c
===================================================================
--- linux-2.6.orig/kernel/futex/syscalls.c
+++ linux-2.6/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;