linux-stable.git/kernel/pid.c, branch v5.15.211

pidfd: refuse access to tasks that have started exiting harder

2026-06-19T11:33:37+00:00

commit 62c4d31d78294bd61cf3403626b789e854357177 upstream.

The recent ptrace fix closed a hole where someone could rely on task->mm
becoming NULL during do_exit() to bypass dumpability checks. This api
here leans on on the very same check and so inherits the fix.

But there is no good reason to let it succeed at all once the target has
entered do_exit(). PF_EXITING is set by exit_signals() at the very top
of do_exit(), before exit_mm() and exit_files() run. Once we observe it,
the task is committed to dying and exit_files() will release the fdtable
shortly.

Fixes: 8649c322f75c ("pid: Implement pidfd_getfd syscall")
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260518-obgleich-petersilie-2d77ccccf9b9@brauner
Signed-off-by: Christian Brauner (Amutable) 
Signed-off-by: Greg Kroah-Hartman

pid: Add a judgment for ns null in pid_nr_ns

2025-10-19T14:21:54+00:00

[ Upstream commit 006568ab4c5ca2309ceb36fa553e390b4aa9c0c7 ]

__task_pid_nr_ns
        ns = task_active_pid_ns(current);
        pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
                if (pid && ns->level <= pid->level) {

Sometimes null is returned for task_active_pid_ns. Then it will trigger kernel panic in pid_nr_ns.

For example:
	Unable to handle kernel NULL pointer dereference at virtual address 0000000000000058
	Mem abort info:
	ESR = 0x0000000096000007
	EC = 0x25: DABT (current EL), IL = 32 bits
	SET = 0, FnV = 0
	EA = 0, S1PTW = 0
	FSC = 0x07: level 3 translation fault
	Data abort info:
	ISV = 0, ISS = 0x00000007, ISS2 = 0x00000000
	CM = 0, WnR = 0, TnD = 0, TagAccess = 0
	GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
	user pgtable: 4k pages, 39-bit VAs, pgdp=00000002175aa000
	[0000000000000058] pgd=08000002175ab003, p4d=08000002175ab003, pud=08000002175ab003, pmd=08000002175be003, pte=0000000000000000
	pstate: 834000c5 (Nzcv daIF +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
	pc : __task_pid_nr_ns+0x74/0xd0
	lr : __task_pid_nr_ns+0x24/0xd0
	sp : ffffffc08001bd10
	x29: ffffffc08001bd10 x28: ffffffd4422b2000 x27: 0000000000000001
	x26: ffffffd442821168 x25: ffffffd442821000 x24: 00000f89492eab31
	x23: 00000000000000c0 x22: ffffff806f5693c0 x21: ffffff806f5693c0
	x20: 0000000000000001 x19: 0000000000000000 x18: 0000000000000000
	x17: 00000000529c6ef0 x16: 00000000529c6ef0 x15: 00000000023a1adc
	x14: 0000000000000003 x13: 00000000007ef6d8 x12: 001167c391c78800
	x11: 00ffffffffffffff x10: 0000000000000000 x9 : 0000000000000001
	x8 : ffffff80816fa3c0 x7 : 0000000000000000 x6 : 49534d702d535449
	x5 : ffffffc080c4c2c0 x4 : ffffffd43ee128c8 x3 : ffffffd43ee124dc
	x2 : 0000000000000000 x1 : 0000000000000001 x0 : ffffff806f5693c0
	Call trace:
	__task_pid_nr_ns+0x74/0xd0
	...
	__handle_irq_event_percpu+0xd4/0x284
	handle_irq_event+0x48/0xb0
	handle_fasteoi_irq+0x160/0x2d8
	generic_handle_domain_irq+0x44/0x60
	gic_handle_irq+0x4c/0x114
	call_on_irq_stack+0x3c/0x74
	do_interrupt_handler+0x4c/0x84
	el1_interrupt+0x34/0x58
	el1h_64_irq_handler+0x18/0x24
	el1h_64_irq+0x68/0x6c
	account_kernel_stack+0x60/0x144
	exit_task_stack_account+0x1c/0x80
	do_exit+0x7e4/0xaf8
	...
	get_signal+0x7bc/0x8d8
	do_notify_resume+0x128/0x828
	el0_svc+0x6c/0x70
	el0t_64_sync_handler+0x68/0xbc
	el0t_64_sync+0x1a8/0x1ac
	Code: 35fffe54 911a02a8 f9400108 b4000128 (b9405a69)
	---[ end trace 0000000000000000 ]---
	Kernel panic - not syncing: Oops: Fatal exception in interrupt

Signed-off-by: gaoxiang17 
Link: https://lore.kernel.org/20250802022123.3536934-1-gxxa03070307@gmail.com
Reviewed-by: Baoquan He 
Signed-off-by: Christian Brauner 
Signed-off-by: Sasha Levin

kernel/pid.c: implement additional checks upon pidfd_create() parameters

2021-08-10T10:53:07+00:00

By adding the pidfd_create() declaration to linux/pid.h, we
effectively expose this function to the rest of the kernel. In order
to avoid any unintended behavior, or set false expectations upon this
function, ensure that constraints are forced upon each of the passed
parameters. This includes the checking of whether the passed struct
pid is a thread-group leader as pidfd creation is currently limited to
such pid types.

Link: https://lore.kernel.org/r/2e9b91c2d529d52a003b8b86c45f866153be9eb5.1628398044.git.repnop@google.com
Signed-off-by: Matthew Bobrowski 
Acked-by: Christian Brauner 
Signed-off-by: Jan Kara

kernel/pid.c: remove static qualifier from pidfd_create()

2021-08-10T10:53:04+00:00

With the idea of returning pidfds from the fanotify API, we need to
expose a mechanism for creating pidfds. We drop the static qualifier
from pidfd_create() and add its declaration to linux/pid.h so that the
pidfd_create() helper can be called from other kernel subsystems
i.e. fanotify.

Link: https://lore.kernel.org/r/0c68653ec32f1b7143301f0231f7ed14062fd82b.1628398044.git.repnop@google.com
Signed-off-by: Matthew Bobrowski 
Acked-by: Christian Brauner 
Signed-off-by: Jan Kara

Merge branch 'exec-update-lock-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

2020-12-16T03:36:48+00:00

Pull exec-update-lock update from Eric Biederman:
 "The key point of this is to transform exec_update_mutex into a
  rw_semaphore so readers can be separated from writers.

  This makes it easier to understand what the holders of the lock are
  doing, and makes it harder to contend or deadlock on the lock.

  The real deadlock fix wound up in perf_event_open"

* 'exec-update-lock-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  exec: Transform exec_update_mutex into a rw_semaphore

Merge tag 'fixes-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

2020-12-15T00:40:27+00:00

Pull misc fixes from Christian Brauner:
 "This contains several fixes which felt worth being combined into a
  single branch:

   - Use put_nsproxy() instead of open-coding it switch_task_namespaces()

   - Kirill's work to unify lifecycle management for all namespaces. The
     lifetime counters are used identically for all namespaces types.
     Namespaces may of course have additional unrelated counters and
     these are not altered. This work allows us to unify the type of the
     counters and reduces maintenance cost by moving the counter in one
     place and indicating that basic lifetime management is identical
     for all namespaces.

   - Peilin's fix adding three byte padding to Dmitry's
     PTRACE_GET_SYSCALL_INFO uapi struct to prevent an info leak.

   - Two smal patches to convert from the /* fall through */ comment
     annotation to the fallthrough keyword annotation which I had taken
     into my branch and into -next before df561f6688fe ("treewide: Use
     fallthrough pseudo-keyword") made it upstream which fixed this
     tree-wide.

     Since I didn't want to invalidate all testing for other commits I
     didn't rebase and kept them"

* tag 'fixes-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  nsproxy: use put_nsproxy() in switch_task_namespaces()
  sys: Convert to the new fallthrough notation
  signal: Convert to the new fallthrough notation
  time: Use generic ns_common::count
  cgroup: Use generic ns_common::count
  mnt: Use generic ns_common::count
  user: Use generic ns_common::count
  pid: Use generic ns_common::count
  ipc: Use generic ns_common::count
  uts: Use generic ns_common::count
  net: Use generic ns_common::count
  ns: Add a common refcount into ns_common
  ptrace: Prevent kernel-infoleak in ptrace_get_syscall_info()

exec: Transform exec_update_mutex into a rw_semaphore

2020-12-10T19:13:32+00:00

Recently syzbot reported[0] that there is a deadlock amongst the users
of exec_update_mutex.  The problematic lock ordering found by lockdep
was:

   perf_event_open  (exec_update_mutex -> ovl_i_mutex)
   chown            (ovl_i_mutex       -> sb_writes)
   sendfile         (sb_writes         -> p->lock)
     by reading from a proc file and writing to overlayfs
   proc_pid_syscall (p->lock           -> exec_update_mutex)

While looking at possible solutions it occured to me that all of the
users and possible users involved only wanted to state of the given
process to remain the same.  They are all readers.  The only writer is
exec.

There is no reason for readers to block on each other.  So fix
this deadlock by transforming exec_update_mutex into a rw_semaphore
named exec_update_lock that only exec takes for writing.

Cc: Jann Horn 
Cc: Vasiliy Kulikov 
Cc: Al Viro 
Cc: Bernd Edlinger 
Cc: Oleg Nesterov 
Cc: Christopher Yeoh 
Cc: Cyrill Gorcunov 
Cc: Sargun Dhillon 
Cc: Christian Brauner 
Cc: Arnd Bergmann 
Cc: Peter Zijlstra 
Cc: Ingo Molnar 
Cc: Arnaldo Carvalho de Melo 
Fixes: eea9673250db ("exec: Add exec_update_mutex to replace cred_guard_mutex")
[0] https://lkml.kernel.org/r/00000000000063640c05ade8e3de@google.com
Reported-by: syzbot+db9cdf3dd1f64252c6ef@syzkaller.appspotmail.com
Link: https://lkml.kernel.org/r/87ft4mbqen.fsf@x220.int.ebiederm.org
Signed-off-by: Eric W. Biederman

pid: move pidfd_get_pid() to pid.c

2020-10-18T16:27:10+00:00

process_madvise syscall needs pidfd_get_pid function to translate pidfd to
pid so this patch move the function to kernel/pid.c.

Suggested-by: Alexander Duyck 
Signed-off-by: Minchan Kim 
Signed-off-by: Andrew Morton 
Reviewed-by: Suren Baghdasaryan 
Reviewed-by: Alexander Duyck 
Reviewed-by: Vlastimil Babka 
Acked-by: Christian Brauner 
Acked-by: David Rientjes 
Cc: Jens Axboe 
Cc: Jann Horn 
Cc: Brian Geffon 
Cc: Daniel Colascione 
Cc: Joel Fernandes 
Cc: Johannes Weiner 
Cc: John Dias 
Cc: Kirill Tkhai 
Cc: Michal Hocko 
Cc: Oleksandr Natalenko 
Cc: Sandeep Patil 
Cc: SeongJae Park 
Cc: SeongJae Park 
Cc: Shakeel Butt 
Cc: Sonny Rao 
Cc: Tim Murray 
Cc: Christian Brauner 
Cc: Florian Weimer 
Cc: 
Link: http://lkml.kernel.org/r/20200302193630.68771-5-minchan@kernel.org
Link: http://lkml.kernel.org/r/20200622192900.22757-3-minchan@kernel.org
Link: https://lkml.kernel.org/r/20200901000633.1920247-3-minchan@kernel.org
Signed-off-by: Linus Torvalds

pidfd: support PIDFD_NONBLOCK in pidfd_open()

2020-09-04T10:34:50+00:00

Introduce PIDFD_NONBLOCK to support non-blocking pidfd file descriptors.

Ever since the introduction of pidfds and more advanced async io various
programming languages such as Rust have grown support for async event
libraries. These libraries are created to help build epoll-based event loops
around file descriptors. A common pattern is to automatically make all file
descriptors they manage to O_NONBLOCK.

For such libraries the EAGAIN error code is treated specially. When a function
is called that returns EAGAIN the function isn't called again until the event
loop indicates the the file descriptor is ready. Supporting EAGAIN when
waiting on pidfds makes such libraries just work with little effort. In the
following patch we will extend waitid() internally to support non-blocking
pidfds.

This introduces a new flag PIDFD_NONBLOCK that is equivalent to O_NONBLOCK.
This follows the same patterns we have for other (anon inode) file descriptors
such as EFD_NONBLOCK, IN_NONBLOCK, SFD_NONBLOCK, TFD_NONBLOCK and the same for
close-on-exec flags.

Suggested-by: Josh Triplett 
Signed-off-by: Christian Brauner 
Reviewed-by: Josh Triplett 
Reviewed-by: Oleg Nesterov 
Cc: Kees Cook 
Cc: Sargun Dhillon 
Cc: Oleg Nesterov 
Link: https://lore.kernel.org/lkml/20200811181236.GA18763@localhost/
Link: https://github.com/joshtriplett/async-pidfd
Link: https://lore.kernel.org/r/20200902102130.147672-2-christian.brauner@ubuntu.com

pid: Use generic ns_common::count

2020-08-19T12:14:06+00:00

Switch over pid namespaces to use the newly introduced common lifetime
counter.

Currently every namespace type has its own lifetime counter which is stored
in the specific namespace struct. The lifetime counters are used
identically for all namespaces types. Namespaces may of course have
additional unrelated counters and these are not altered.

This introduces a common lifetime counter into struct ns_common. The
ns_common struct encompasses information that all namespaces share. That
should include the lifetime counter since its common for all of them.

It also allows us to unify the type of the counters across all namespaces.
Most of them use refcount_t but one uses atomic_t and at least one uses
kref. Especially the last one doesn't make much sense since it's just a
wrapper around refcount_t since 2016 and actually complicates cleanup
operations by having to use container_of() to cast the correct namespace
struct out of struct ns_common.

Having the lifetime counter for the namespaces in one place reduces
maintenance cost. Not just because after switching all namespaces over we
will have removed more code than we added but also because the logic is
more easily understandable and we indicate to the user that the basic
lifetime requirements for all namespaces are currently identical.

Signed-off-by: Kirill Tkhai 
Reviewed-by: Kees Cook 
Acked-by: Christian Brauner 
Link: https://lore.kernel.org/r/159644979226.604812.7512601754841882036.stgit@localhost.localdomain
Signed-off-by: Christian Brauner