From e6b899f08066e744f89df16ceb782e06868bd148 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Thu, 26 Feb 2026 14:50:09 +0100 Subject: [PATCH 1/4] nsfs: tighten permission checks for ns iteration ioctls Even privileged services should not necessarily be able to see other privileged service's namespaces so they can't leak information to each other. Use may_see_all_namespaces() helper that centralizes this policy until the nstree adapts. Link: https://patch.msgid.link/20260226-work-visibility-fixes-v1-1-d2c2853313bd@kernel.org Fixes: a1d220d9dafa ("nsfs: iterate through mount namespaces") Reviewed-by: Jeff Layton Cc: stable@kernel.org # v6.12+ Signed-off-by: Christian Brauner --- fs/nsfs.c | 13 +++++++++++++ include/linux/ns_common.h | 2 ++ kernel/nscommon.c | 6 ++++++ 3 files changed, 21 insertions(+) diff --git a/fs/nsfs.c b/fs/nsfs.c index db91de208645..be36c10c38cf 100644 --- a/fs/nsfs.c +++ b/fs/nsfs.c @@ -199,6 +199,17 @@ static bool nsfs_ioctl_valid(unsigned int cmd) return false; } +static bool may_use_nsfs_ioctl(unsigned int cmd) +{ + switch (_IOC_NR(cmd)) { + case _IOC_NR(NS_MNT_GET_NEXT): + fallthrough; + case _IOC_NR(NS_MNT_GET_PREV): + return may_see_all_namespaces(); + } + return true; +} + static long ns_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg) { @@ -214,6 +225,8 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl, if (!nsfs_ioctl_valid(ioctl)) return -ENOIOCTLCMD; + if (!may_use_nsfs_ioctl(ioctl)) + return -EPERM; ns = get_proc_ns(file_inode(filp)); switch (ioctl) { diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h index 825f5865bfc5..c8e227a3f9e2 100644 --- a/include/linux/ns_common.h +++ b/include/linux/ns_common.h @@ -55,6 +55,8 @@ static __always_inline bool is_ns_init_id(const struct ns_common *ns) #define ns_common_free(__ns) __ns_common_free(to_ns_common((__ns))) +bool may_see_all_namespaces(void); + static __always_inline __must_check int __ns_ref_active_read(const struct ns_common *ns) { return atomic_read(&ns->__ns_ref_active); diff --git a/kernel/nscommon.c b/kernel/nscommon.c index bdc3c86231d3..3166c1fd844a 100644 --- a/kernel/nscommon.c +++ b/kernel/nscommon.c @@ -309,3 +309,9 @@ void __ns_ref_active_get(struct ns_common *ns) return; } } + +bool may_see_all_namespaces(void) +{ + return (task_active_pid_ns(current) == &init_pid_ns) && + ns_capable_noaudit(init_pid_ns.user_ns, CAP_SYS_ADMIN); +} From d2324a9317f00013facb0ba00b00440e19d2af5e Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Thu, 26 Feb 2026 14:50:10 +0100 Subject: [PATCH 2/4] nsfs: tighten permission checks for handle opening Even privileged services should not necessarily be able to see other privileged service's namespaces so they can't leak information to each other. Use may_see_all_namespaces() helper that centralizes this policy until the nstree adapts. Link: https://patch.msgid.link/20260226-work-visibility-fixes-v1-2-d2c2853313bd@kernel.org Fixes: 5222470b2fbb ("nsfs: support file handles") Reviewed-by: Jeff Layton Cc: stable@kernel.org # v6.18+ Signed-off-by: Christian Brauner --- fs/nsfs.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/nsfs.c b/fs/nsfs.c index be36c10c38cf..c215878d55e8 100644 --- a/fs/nsfs.c +++ b/fs/nsfs.c @@ -627,7 +627,7 @@ static struct dentry *nsfs_fh_to_dentry(struct super_block *sb, struct fid *fh, return ERR_PTR(-EOPNOTSUPP); } - if (owning_ns && !ns_capable(owning_ns, CAP_SYS_ADMIN)) { + if (owning_ns && !may_see_all_namespaces()) { ns->ops->put(ns); return ERR_PTR(-EPERM); } From 8d76afe84fa2babf604b3c173730d4d2b067e361 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Thu, 26 Feb 2026 14:50:11 +0100 Subject: [PATCH 3/4] nstree: tighten permission checks for listing Even privileged services should not necessarily be able to see other privileged service's namespaces so they can't leak information to each other. Use may_see_all_namespaces() helper that centralizes this policy until the nstree adapts. Link: https://patch.msgid.link/20260226-work-visibility-fixes-v1-3-d2c2853313bd@kernel.org Fixes: 76b6f5dfb3fd ("nstree: add listns()") Reviewed-by: Jeff Layton Cc: stable@kernel.org # v6.19+ Signed-off-by: Christian Brauner --- kernel/nstree.c | 29 ++++------------------------- 1 file changed, 4 insertions(+), 25 deletions(-) diff --git a/kernel/nstree.c b/kernel/nstree.c index f36c59e6951d..6d12e5900ac0 100644 --- a/kernel/nstree.c +++ b/kernel/nstree.c @@ -515,32 +515,11 @@ static inline bool __must_check ns_requested(const struct klistns *kls, static inline bool __must_check may_list_ns(const struct klistns *kls, struct ns_common *ns) { - if (kls->user_ns) { - if (kls->userns_capable) - return true; - } else { - struct ns_common *owner; - struct user_namespace *user_ns; - - owner = ns_owner(ns); - if (owner) - user_ns = to_user_ns(owner); - else - user_ns = &init_user_ns; - if (ns_capable_noaudit(user_ns, CAP_SYS_ADMIN)) - return true; - } - + if (kls->user_ns && kls->userns_capable) + return true; if (is_current_namespace(ns)) return true; - - if (ns->ns_type != CLONE_NEWUSER) - return false; - - if (ns_capable_noaudit(to_user_ns(ns), CAP_SYS_ADMIN)) - return true; - - return false; + return may_see_all_namespaces(); } static inline void ns_put(struct ns_common *ns) @@ -600,7 +579,7 @@ static ssize_t do_listns_userns(struct klistns *kls) ret = 0; head = &to_ns_common(kls->user_ns)->ns_owner_root.ns_list_head; - kls->userns_capable = ns_capable_noaudit(kls->user_ns, CAP_SYS_ADMIN); + kls->userns_capable = may_see_all_namespaces(); rcu_read_lock(); From 4c7b2ec23cc5d880e3ffe35e8c2aad686b67723a Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Thu, 26 Feb 2026 14:50:12 +0100 Subject: [PATCH 4/4] selftests: fix mntns iteration selftests Now that we changed permission checking make sure that we reflect that in the selftests. Link: https://patch.msgid.link/20260226-work-visibility-fixes-v1-4-d2c2853313bd@kernel.org Fixes: 9d87b1067382 ("selftests: add tests for mntns iteration") Reviewed-by: Jeff Layton Cc: stable@kernel.org # v6.14+ Signed-off-by: Christian Brauner --- .../filesystems/nsfs/iterate_mntns.c | 25 +++++++++++-------- 1 file changed, 15 insertions(+), 10 deletions(-) diff --git a/tools/testing/selftests/filesystems/nsfs/iterate_mntns.c b/tools/testing/selftests/filesystems/nsfs/iterate_mntns.c index 61e55dfbf121..e19ff8168baf 100644 --- a/tools/testing/selftests/filesystems/nsfs/iterate_mntns.c +++ b/tools/testing/selftests/filesystems/nsfs/iterate_mntns.c @@ -37,17 +37,20 @@ FIXTURE(iterate_mount_namespaces) { __u64 mnt_ns_id[MNT_NS_COUNT]; }; +static inline bool mntns_in_list(__u64 *mnt_ns_id, struct mnt_ns_info *info) +{ + for (int i = 0; i < MNT_NS_COUNT; i++) { + if (mnt_ns_id[i] == info->mnt_ns_id) + return true; + } + return false; +} + FIXTURE_SETUP(iterate_mount_namespaces) { for (int i = 0; i < MNT_NS_COUNT; i++) self->fd_mnt_ns[i] = -EBADF; - /* - * Creating a new user namespace let's us guarantee that we only see - * mount namespaces that we did actually create. - */ - ASSERT_EQ(unshare(CLONE_NEWUSER), 0); - for (int i = 0; i < MNT_NS_COUNT; i++) { struct mnt_ns_info info = {}; @@ -75,13 +78,15 @@ TEST_F(iterate_mount_namespaces, iterate_all_forward) fd_mnt_ns_cur = fcntl(self->fd_mnt_ns[0], F_DUPFD_CLOEXEC); ASSERT_GE(fd_mnt_ns_cur, 0); - for (;; count++) { + for (;;) { struct mnt_ns_info info = {}; int fd_mnt_ns_next; fd_mnt_ns_next = ioctl(fd_mnt_ns_cur, NS_MNT_GET_NEXT, &info); if (fd_mnt_ns_next < 0 && errno == ENOENT) break; + if (mntns_in_list(self->mnt_ns_id, &info)) + count++; ASSERT_GE(fd_mnt_ns_next, 0); ASSERT_EQ(close(fd_mnt_ns_cur), 0); fd_mnt_ns_cur = fd_mnt_ns_next; @@ -96,13 +101,15 @@ TEST_F(iterate_mount_namespaces, iterate_all_backwards) fd_mnt_ns_cur = fcntl(self->fd_mnt_ns[MNT_NS_LAST_INDEX], F_DUPFD_CLOEXEC); ASSERT_GE(fd_mnt_ns_cur, 0); - for (;; count++) { + for (;;) { struct mnt_ns_info info = {}; int fd_mnt_ns_prev; fd_mnt_ns_prev = ioctl(fd_mnt_ns_cur, NS_MNT_GET_PREV, &info); if (fd_mnt_ns_prev < 0 && errno == ENOENT) break; + if (mntns_in_list(self->mnt_ns_id, &info)) + count++; ASSERT_GE(fd_mnt_ns_prev, 0); ASSERT_EQ(close(fd_mnt_ns_cur), 0); fd_mnt_ns_cur = fd_mnt_ns_prev; @@ -125,7 +132,6 @@ TEST_F(iterate_mount_namespaces, iterate_forward) ASSERT_GE(fd_mnt_ns_next, 0); ASSERT_EQ(close(fd_mnt_ns_cur), 0); fd_mnt_ns_cur = fd_mnt_ns_next; - ASSERT_EQ(info.mnt_ns_id, self->mnt_ns_id[i]); } } @@ -144,7 +150,6 @@ TEST_F(iterate_mount_namespaces, iterate_backward) ASSERT_GE(fd_mnt_ns_prev, 0); ASSERT_EQ(close(fd_mnt_ns_cur), 0); fd_mnt_ns_cur = fd_mnt_ns_prev; - ASSERT_EQ(info.mnt_ns_id, self->mnt_ns_id[i]); } }