Merge tag 'namespace-6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull namespace updates from Christian Brauner:
 "This contains substantial namespace infrastructure changes including a new
  system call, active reference counting, and extensive header cleanups.
  The branch depends on the shared kbuild branch for -fms-extensions support.

  Features:

   - listns() system call

     Add a new listns() system call that allows userspace to iterate
     through namespaces in the system. This provides a programmatic
     interface to discover and inspect namespaces, addressing
     longstanding limitations:

     Currently, there is no direct way for userspace to enumerate
     namespaces. Applications must resort to scanning /proc/*/ns/ across
     all processes, which is:
      - Inefficient - requires iterating over all processes
      - Incomplete - misses namespaces not attached to any running
        process but kept alive by file descriptors, bind mounts, or
        parent references
      - Permission-heavy - requires access to /proc for many processes
      - No ordering or ownership information
      - No filtering per namespace type

     The listns() system call solves these problems:

       ssize_t listns(const struct ns_id_req *req, u64 *ns_ids,
                      size_t nr_ns_ids, unsigned int flags);

       struct ns_id_req {
             __u32 size;
             __u32 spare;
             __u64 ns_id;
             struct /* listns */ {
                     __u32 ns_type;
                     __u32 spare2;
                     __u64 user_ns_id;
             };
       };

     Features include:
      - Pagination support for large namespace sets
      - Filtering by namespace type (MNT_NS, NET_NS, USER_NS, etc.)
      - Filtering by owning user namespace
      - Permission checks respecting namespace isolation

   - Active Reference Counting

     Introduce an active reference count that tracks namespace
     visibility to userspace. A namespace is visible in the following
     cases:
      - The namespace is in use by a task
      - The namespace is persisted through a VFS object (namespace file
        descriptor or bind-mount)
      - The namespace is a hierarchical type and is the parent of child
        namespaces

     The active reference count does not regulate lifetime (that's still
     done by the normal reference count) - it only regulates visibility
     to namespace file handles and listns().

     This prevents resurrection of namespaces that are pinned only for
     internal kernel reasons (e.g., user namespaces held by
     file->f_cred, lazy TLB references on idle CPUs, etc.) which should
     not be accessible via (1)-(3).

   - Unified Namespace Tree

     Introduce a unified tree structure for all namespaces with:
      - Fixed IDs assigned to initial namespaces
      - Lookup based solely on inode number
      - Maintained list of owned namespaces per user namespace
      - Simplified rbtree comparison helpers

   Cleanups

    - Header Reorganization:
      - Move namespace types into separate header (ns_common_types.h)
      - Decouple nstree from ns_common header
      - Move nstree types into separate header
      - Switch to new ns_tree_{node,root} structures with helper functions
      - Use guards for ns_tree_lock

   - Initial Namespace Reference Count Optimization
      - Make all reference counts on initial namespaces a nop to avoid
        pointless cacheline ping-pong for namespaces that can never go
        away
      - Drop custom reference count initialization for initial namespaces
      - Add NS_COMMON_INIT() macro and use it for all namespaces
      - pid: rely on common reference count behavior

   - Miscellaneous Cleanups
      - Rename exit_task_namespaces() to exit_nsproxy_namespaces()
      - Rename is_initial_namespace() and make argument const
      - Use boolean to indicate anonymous mount namespace
      - Simplify owner list iteration in nstree
      - nsfs: raise SB_I_NODEV, SB_I_NOEXEC, and DCACHE_DONTCACHE explicitly
      - nsfs: use inode_just_drop()
      - pidfs: raise DCACHE_DONTCACHE explicitly
      - pidfs: simplify PIDFD_GET__NAMESPACE ioctls
      - libfs: allow to specify s_d_flags
      - cgroup: add cgroup namespace to tree after owner is set
      - nsproxy: fix free_nsproxy() and simplify create_new_namespaces()

  Fixes:

   - setns(pidfd, ...) race condition

     Fix a subtle race when using pidfds with setns(). When the target
     task exits after prepare_nsset() but before commit_nsset(), the
     namespace's active reference count might have been dropped. If
     setns() then installs the namespaces, it would bump the active
     reference count from zero without taking the required reference on
     the owner namespace, leading to underflow when later decremented.

     The fix resurrects the ownership chain if necessary - if the caller
     succeeded in grabbing passive references, the setns() should
     succeed even if the target task exits or gets reaped.

   - Return EFAULT on put_user() error instead of success

   - Make sure references are dropped outside of RCU lock (some
     namespaces like mount namespace sleep when putting the last
     reference)

   - Don't skip active reference count initialization for network
     namespace

   - Add asserts for active refcount underflow

   - Add asserts for initial namespace reference counts (both passive
     and active)

   - ipc: enable is_ns_init_id() assertions

   - Fix kernel-doc comments for internal nstree functions

   - Selftests
      - 15 active reference count tests
      - 9 listns() functionality tests
      - 7 listns() permission tests
      - 12 inactive namespace resurrection tests
      - 3 threaded active reference count tests
      - commit_creds() active reference tests
      - Pagination and stress tests
      - EFAULT handling test
      - nsid tests fixes"

* tag 'namespace-6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (103 commits)
  pidfs: simplify PIDFD_GET_<type>_NAMESPACE ioctls
  nstree: fix kernel-doc comments for internal functions
  nsproxy: fix free_nsproxy() and simplify create_new_namespaces()
  selftests/namespaces: fix nsid tests
  ns: drop custom reference count initialization for initial namespaces
  pid: rely on common reference count behavior
  ns: add asserts for initial namespace active reference counts
  ns: add asserts for initial namespace reference counts
  ns: make all reference counts on initial namespace a nop
  ipc: enable is_ns_init_id() assertions
  fs: use boolean to indicate anonymous mount namespace
  ns: rename is_initial_namespace()
  ns: make is_initial_namespace() argument const
  nstree: use guards for ns_tree_lock
  nstree: simplify owner list iteration
  nstree: switch to new structures
  nstree: add helper to operate on struct ns_tree_{node,root}
  nstree: move nstree types into separate header
  nstree: decouple from ns_common header
  ns: move namespace types into separate header
  ...

16 files changed, 16 insertions, 0 deletions

diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index 16dca28ebf17..3fed97478058 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -509,3 +509,4 @@
 577	common	open_tree_attr			sys_open_tree_attr
 578	common	file_getattr			sys_file_getattr
 579	common	file_setattr			sys_file_setattr
+580	common	listns				sys_listns
diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index b07e699aaa3c..fd09afae72a2 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -484,3 +484,4 @@
 467	common	open_tree_attr			sys_open_tree_attr
 468	common	file_getattr			sys_file_getattr
 469	common	file_setattr			sys_file_setattr
+470	common	listns				sys_listns
diff --git a/arch/arm64/tools/syscall_32.tbl b/arch/arm64/tools/syscall_32.tbl
index 8d9088bc577d..8cdfe5d4dac9 100644
--- a/arch/arm64/tools/syscall_32.tbl
+++ b/arch/arm64/tools/syscall_32.tbl
@@ -481,3 +481,4 @@
 467	common	open_tree_attr			sys_open_tree_attr
 468	common	file_getattr			sys_file_getattr
 469	common	file_setattr			sys_file_setattr
+470	common	listns				sys_listns
diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index f41d38dfbf13..871a5d67bf41 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -469,3 +469,4 @@
 467	common	open_tree_attr			sys_open_tree_attr
 468	common	file_getattr			sys_file_getattr
 469	common	file_setattr			sys_file_setattr
+470	common	listns				sys_listns
diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index 580af574fe73..022fc85d94b3 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -475,3 +475,4 @@
 467	common	open_tree_attr			sys_open_tree_attr
 468	common	file_getattr			sys_file_getattr
 469	common	file_setattr			sys_file_setattr
+470	common	listns				sys_listns
diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
index d824ffe9a014..8cedc83c3266 100644
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
@@ -408,3 +408,4 @@
 467	n32	open_tree_attr			sys_open_tree_attr
 468	n32	file_getattr			sys_file_getattr
 469	n32	file_setattr			sys_file_setattr
+470	n32	listns				sys_listns
diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
index 7a7049c2c307..9b92bddf06b5 100644
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
@@ -384,3 +384,4 @@
 467	n64	open_tree_attr			sys_open_tree_attr
 468	n64	file_getattr			sys_file_getattr
 469	n64	file_setattr			sys_file_setattr
+470	n64	listns				sys_listns
diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
index d330274f0601..f810b8a55716 100644
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
@@ -457,3 +457,4 @@
 467	o32	open_tree_attr			sys_open_tree_attr
 468	o32	file_getattr			sys_file_getattr
 469	o32	file_setattr			sys_file_setattr
+470	o32	listns				sys_listns
diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
index 88a788a7b18d..39bdacaa530b 100644
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl
@@ -468,3 +468,4 @@
 467	common	open_tree_attr			sys_open_tree_attr
 468	common	file_getattr			sys_file_getattr
 469	common	file_setattr			sys_file_setattr
+470	common	listns				sys_listns
diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index b453e80dfc00..ec4458cdb97b 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -560,3 +560,4 @@
 467	common	open_tree_attr			sys_open_tree_attr
 468	common	file_getattr			sys_file_getattr
 469	common	file_setattr			sys_file_setattr
+470	common	listns				sys_listns
diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index 8a6744d658db..5863787ab036 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@ -472,3 +472,4 @@
 467  common	open_tree_attr		sys_open_tree_attr		sys_open_tree_attr
 468  common	file_getattr		sys_file_getattr		sys_file_getattr
 469  common	file_setattr		sys_file_setattr		sys_file_setattr
+470  common	listns			sys_listns			sys_listns
diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index 5e9c9eff5539..969c11325ade 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@ -473,3 +473,4 @@
 467	common	open_tree_attr			sys_open_tree_attr
 468	common	file_getattr			sys_file_getattr
 469	common	file_setattr			sys_file_setattr
+470	common	listns				sys_listns
diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index ebb7d06d1044..39aa26b6a50b 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@ -515,3 +515,4 @@
 467	common	open_tree_attr			sys_open_tree_attr
 468	common	file_getattr			sys_file_getattr
 469	common	file_setattr			sys_file_setattr
+470	common	listns				sys_listns
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 4877e16da69a..e979a3eac7a3 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -475,3 +475,4 @@
 467	i386	open_tree_attr		sys_open_tree_attr
 468	i386	file_getattr		sys_file_getattr
 469	i386	file_setattr		sys_file_setattr
+470	i386	listns			sys_listns
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index ced2a1deecd7..8a4ac4841be6 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -394,6 +394,7 @@
 467	common	open_tree_attr		sys_open_tree_attr
 468	common	file_getattr		sys_file_getattr
 469	common	file_setattr		sys_file_setattr
+470	common	listns			sys_listns
 
 #
 # Due to a historical design error, certain syscalls are numbered differently
diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
index 374e4cb788d8..438a3b170402 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@ -440,3 +440,4 @@
 467	common	open_tree_attr			sys_open_tree_attr
 468	common	file_getattr			sys_file_getattr
 469	common	file_setattr			sys_file_setattr
+470	common	listns				sys_listns