[tip: locking/core] futex: Validate futex value against futex size

[tip-bot2 for peterz@xxxxxxxxxxxxx]

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     698eb826383616ce0e817d2384da6413d1439fb6
Gitweb:        https://git.kernel.org/tip/698eb826383616ce0e817d2384da6413d1439fb6
Author:        peterz@xxxxxxxxxxxxx <peterz@xxxxxxxxxxxxx>
AuthorDate:    Thu, 21 Sep 2023 12:45:09 +02:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 21 Sep 2023 19:22:06 +02:00

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@xxxxxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230921105247.828934099@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
---
 kernel/futex/futex.h    | 10 ++++++++++
 kernel/futex/syscalls.c |  3 +++
 2 files changed, 13 insertions(+)

diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
index 68fc052..a3f1fce 100644
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -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
diff --git a/kernel/futex/syscalls.c b/kernel/futex/syscalls.c
index 948ac24..2339f9c 100644
--- a/kernel/futex/syscalls.c
+++ b/kernel/futex/syscalls.c
@@ -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;