From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-101.mta0.migadu.com [91.218.175.101]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 26CA43A9870 for ; Sun, 27 Sep 2026 09:55:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.101 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790502905; cv=none; b=sL+1Oy22Ocj0+FYwBU7RGkaI9k/vV/EZmXygGFiRfVwKqMeNs30aJIJjcN5xjDWFMzWa4YlulSCRKadHwkuEAEWve4IegWZFXkikmdYYylQFfAEO6xzQbNqyqCnU/eYhhMSEWnh2sgRjF8e/EIdAp6QcSU8bD4nBCyd7Sc1HCKM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790502905; c=relaxed/simple; bh=MnUziHyI7x/kpNN1Hc2LF0E+uP7SX1LMj6VKOBxKczs=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=cHNpmrrzEkNhvRJx/2jfFlae39MH92CNa9DS9iWXys/6YCwFyWvzr2rS9NeBZFMMQo806qLMbIDchzhofUUpZixR0X6mW6ez7nxSaBYFz9LdKGW+XD/jrj4/bm0j12KGotXqoWZo1wkXPS6igQCN8VdC28hAio/aAEiqTI3P0rw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=gABBMUzM; arc=none smtp.client-ip=91.218.175.101 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="gABBMUzM" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=MnUziHyI7x/kpNN1Hc2LF0E+uP7SX1LMj6VKOBxKczs=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1790502899; v=1; x=1791107699; b=gABBMUzMEROqx3xzvGdiOWTjsJ7YOFC6Ecl4Kij2r4ubdtxSmfoq77BEBGExUuBd2+S4i2Fc 8oMYaZ6mdOHsantFFe3Tc0K4DcxQ83Jy+/faX8B6L1Plo0Uwh171x/HnGd5qbP+Xx0+x9OQkt1Y DlJ+SU0dYJRPOs6h8gFWlVKM= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 66a51e8696da171c; Sun, 27 Sep 2026 09:54:59 +0000 X-Mizu-Trace-ID: 66a51e8696da171c X-Migadu-Flow: FLOW_OUT From: Tao Cui To: Christian Brauner , Andrew Morton Cc: linux-kernel@vger.kernel.org, Pavel Tikhomirov , Michal Grzedzicki , Alexey Gladkov , "Liam R . Howlett" , Jan Kara , cui.tao@linux.dev, Tao Cui Subject: [PATCH] fork: fix active reference underflow on unshare() failure Date: Sun, 27 Sep 2026 17:54:50 +0800 Message-ID: <20260927095450.3017586-1-cui.tao@linux.dev> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Tao Cui When set_cred_ucounts() fails in ksys_unshare() the new nsproxy is released with put_nsproxy(). But the nsproxy has not been installed at this point; it is only marked as active once switch_task_namespaces() installs it, which happens after all failure points. Dropping the last reference therefore deactivates it and puts the active reference of every namespace it points to: for namespaces created by this unshare() call the active count underflows to -1, and for namespaces carried over from the caller a live active reference of the still-running task is dropped, which makes them disappear from nsfs file handles and listns and causes a cascading underflow at task exit. Use nsproxy_free() on this error path, which drops the regular references without touching the active ones, like the setns() failure paths already do; see commit cefd55bd2159 ("nsproxy: fix free_nsproxy() and simplify create_new_namespaces()"). Fixes: a98621a0f187a ("unshare: fix nsproxy leak in ksys_unshare() on set_cred_ucounts() failure") Link: https://lore.kernel.org/r/20251118064552.936962-1-ptikhomirov@virtuozzo.com Link: https://lore.kernel.org/r/20260213193959.2556730-1-mge@meta.com Signed-off-by: Tao Cui --- include/linux/nsproxy.h | 1 + kernel/fork.c | 2 +- kernel/nsproxy.c | 2 +- 3 files changed, 3 insertions(+), 2 deletions(-) diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h index 5a67648721c7d..dc2447f5f0924 100644 --- a/include/linux/nsproxy.h +++ b/include/linux/nsproxy.h @@ -100,6 +100,7 @@ void exit_cred_namespaces(struct task_struct *tsk); void switch_task_namespaces(struct task_struct *tsk, struct nsproxy *new); int exec_task_namespaces(void); void deactivate_nsproxy(struct nsproxy *ns); +void nsproxy_free(struct nsproxy *ns); int unshare_nsproxy_namespaces(unsigned long, struct nsproxy **, struct cred *, struct fs_struct *); int __init nsproxy_cache_init(void); diff --git a/kernel/fork.c b/kernel/fork.c index d458d85d7a656..11e16554daa61 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -3324,7 +3324,7 @@ int ksys_unshare(unsigned long unshare_flags) bad_unshare_cleanup_nsproxy: if (new_nsproxy) - put_nsproxy(new_nsproxy); + nsproxy_free(new_nsproxy); bad_unshare_cleanup_cred: if (new_cred) put_cred(new_cred); diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c index 0f1b208d8eeff..454427b09ed97 100644 --- a/kernel/nsproxy.c +++ b/kernel/nsproxy.c @@ -61,7 +61,7 @@ static inline struct nsproxy *create_nsproxy(void) return nsproxy; } -static inline void nsproxy_free(struct nsproxy *ns) +void nsproxy_free(struct nsproxy *ns) { put_mnt_ns(ns->mnt_ns); put_uts_ns(ns->uts_ns); -- 2.43.0