linux-kernel - [tip: locking/urgent] futex: Allow to resize the private local hash

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <174963360666.406.17688851529613883167.tip-bot2@tip-bot2>
Date: Wed, 11 Jun 2025 09:20:06 -0000
From: "tip-bot2 for Sebastian Andrzej Siewior" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: locking/urgent] futex: Allow to resize the private local hash

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

Commit-ID:     cdd0f803c1f9b69785f5ff865864cfea11081c91
Gitweb:        https://git.kernel.org/tip/cdd0f803c1f9b69785f5ff865864cfea11081c91
Author:        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
AuthorDate:    Mon, 02 Jun 2025 13:00:27 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Thu, 05 Jun 2025 14:37:59 +02:00

futex: Allow to resize the private local hash

On 2025-06-01 15:39:47 [+0800], Lai, Yi wrote:
> Hi Sebastian Andrzej Siewior,
Hi Yi,
> Greetings!
>
> I used Syzkaller and found that there is KASAN: null-ptr-deref Read in __futex_pivot_hash in linux-next next-20250527.
>
> After bisection and the first bad commit is:
> "
> bd54df5ea7ca futex: Allow to resize the private local hash
> "

Thank you for the report. Next time please trim your report. There is no
need to put your report in the middle of the patch.

The following fixes it:

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20250602110027.wfqbHgzb@linutronix.de
---
 kernel/futex/core.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index b652d2f..33b3643 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -1629,6 +1629,16 @@ again:
 		mm->futex_phash_new = NULL;
 
 		if (fph) {
+			if (cur && !cur->hash_mask) {
+				/*
+				 * If two threads simultaneously request the global
+				 * hash then the first one performs the switch,
+				 * the second one returns here.
+				 */
+				free = fph;
+				mm->futex_phash_new = new;
+				return -EBUSY;
+			}
 			if (cur && !new) {
 				/*
 				 * If we have an existing hash, but do not yet have