From 0b6f31a3c0b16066f812e94b52a704174a6f23cd Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 30 Sep 2026 15:32:08 +0200 Subject: unshare: don't drop active namespace references that were never taken Active references on the namespaces of an nsproxy are taken when the nsproxy is installed into a task in switch_task_namespaces() and copy_namespaces() and dropped again by put_nsproxy() through deactivate_nsproxy(). But ksys_unshare() calls put_nsproxy() on an nsproxy that was never installed when set_cred_ucounts() fails. The new namespaces of that nsproxy go from zero to minus one and the namespaces shared with the caller lose a reference that belongs to the nsproxy the caller keeps using: WARNING: kernel/nscommon.c:171 at __ns_ref_active_put+0x1cd/0x230 nsproxy_ns_active_put deactivate_nsproxy ksys_unshare Afterwards the namespaces the caller lives in aren't listed by listns() anymore. set_cred_ucounts() only fails when alloc_ucounts() can't allocate and it only allocates when the real uid of the caller differs from its effective uid. Commit cefd55bd2159 ("nsproxy: fix free_nsproxy() and simplify create_new_namespaces()") separated the two cases on purpose. nsproxy_free() frees an nsproxy that was prepared but never installed and that's what a failed setns() uses in put_nsset(). Export it and use it for a failed unshare() as well. Fixes: a98621a0f187 ("unshare: fix nsproxy leak in ksys_unshare() on set_cred_ucounts() failure") Cc: stable@vger.kernel.org # v7.1+ Link: https://patch.msgid.link/20260930-work-mount-fixes-3-v1-16-be34c83956ae@kernel.org Signed-off-by: Christian Brauner (Amutable) --- kernel/nsproxy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/nsproxy.c') diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c index d9d3d5973bf5..3fb1595a4a59 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); -- cgit v1.2.3