[tip: locking/urgent] futex: Handle invalid node numbers supplied by user

["tip-bot2 for Peter Zijlstra" <tip-bot2@linutronix.de>]

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

Commit-ID:     8337204c58899fe422db765b481711eb2d95eb0b
Gitweb:        https://git.kernel.org/tip/8337204c58899fe422db765b481711eb2d95eb0b
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Wed, 28 May 2025 10:55:21 +02:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 05 Jun 2025 14:37:58 +02:00

futex: Handle invalid node numbers supplied by user

syzbot used a negative node number which was not rejected early and led
to invalid memory access in node_possible().

Reject negative node numbers except for FUTEX_NO_NODE.

[bigeasy: Keep the FUTEX_NO_NODE check]

Closes: https://lore.kernel.org/all/6835bfe3.a70a0220.253bc2.00b5.GAE@google.com/
Fixes: cec199c5e39bd ("futex: Implement FUTEX2_NUMA")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reported-by: syzbot+9afaf6749e3a7aa1bdf3@syzkaller.appspotmail.com
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250528085521.1938355-4-bigeasy@linutronix.de
---
 kernel/futex/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index 565f971..b652d2f 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -583,8 +583,8 @@ int get_futex_key(u32 __user *uaddr, unsigned int flags, union futex_key *key,
 		if (futex_get_value(&node, naddr))
 			return -EFAULT;
 
-		if (node != FUTEX_NO_NODE &&
-		    (node >= MAX_NUMNODES || !node_possible(node)))
+		if ((node != FUTEX_NO_NODE) &&
+		    ((unsigned int)node >= MAX_NUMNODES || !node_possible(node)))
 			return -EINVAL;
 	}