| From 0711f0d7050b9e07c44bc159bbc64ac0a1022c7f Mon Sep 17 00:00:00 2001 |
| From: Mark Rutland <mark.rutland@arm.com> |
| Date: Fri, 4 Jun 2021 20:01:14 -0700 |
| Subject: pid: take a reference when initializing `cad_pid` |
| |
| From: Mark Rutland <mark.rutland@arm.com> |
| |
| commit 0711f0d7050b9e07c44bc159bbc64ac0a1022c7f upstream. |
| |
| During boot, kernel_init_freeable() initializes `cad_pid` to the init |
| task's struct pid. Later on, we may change `cad_pid` via a sysctl, and |
| when this happens proc_do_cad_pid() will increment the refcount on the |
| new pid via get_pid(), and will decrement the refcount on the old pid |
| via put_pid(). As we never called get_pid() when we initialized |
| `cad_pid`, we decrement a reference we never incremented, can therefore |
| free the init task's struct pid early. As there can be dangling |
| references to the struct pid, we can later encounter a use-after-free |
| (e.g. when delivering signals). |
| |
| This was spotted when fuzzing v5.13-rc3 with Syzkaller, but seems to |
| have been around since the conversion of `cad_pid` to struct pid in |
| commit 9ec52099e4b8 ("[PATCH] replace cad_pid by a struct pid") from the |
| pre-KASAN stone age of v2.6.19. |
| |
| Fix this by getting a reference to the init task's struct pid when we |
| assign it to `cad_pid`. |
| |
| Full KASAN splat below. |
| |
| ================================================================== |
| BUG: KASAN: use-after-free in ns_of_pid include/linux/pid.h:153 [inline] |
| BUG: KASAN: use-after-free in task_active_pid_ns+0xc0/0xc8 kernel/pid.c:509 |
| Read of size 4 at addr ffff23794dda0004 by task syz-executor.0/273 |
| |
| CPU: 1 PID: 273 Comm: syz-executor.0 Not tainted 5.12.0-00001-g9aef892b2d15 #1 |
| Hardware name: linux,dummy-virt (DT) |
| Call trace: |
| ns_of_pid include/linux/pid.h:153 [inline] |
| task_active_pid_ns+0xc0/0xc8 kernel/pid.c:509 |
| do_notify_parent+0x308/0xe60 kernel/signal.c:1950 |
| exit_notify kernel/exit.c:682 [inline] |
| do_exit+0x2334/0x2bd0 kernel/exit.c:845 |
| do_group_exit+0x108/0x2c8 kernel/exit.c:922 |
| get_signal+0x4e4/0x2a88 kernel/signal.c:2781 |
| do_signal arch/arm64/kernel/signal.c:882 [inline] |
| do_notify_resume+0x300/0x970 arch/arm64/kernel/signal.c:936 |
| work_pending+0xc/0x2dc |
| |
| Allocated by task 0: |
| slab_post_alloc_hook+0x50/0x5c0 mm/slab.h:516 |
| slab_alloc_node mm/slub.c:2907 [inline] |
| slab_alloc mm/slub.c:2915 [inline] |
| kmem_cache_alloc+0x1f4/0x4c0 mm/slub.c:2920 |
| alloc_pid+0xdc/0xc00 kernel/pid.c:180 |
| copy_process+0x2794/0x5e18 kernel/fork.c:2129 |
| kernel_clone+0x194/0x13c8 kernel/fork.c:2500 |
| kernel_thread+0xd4/0x110 kernel/fork.c:2552 |
| rest_init+0x44/0x4a0 init/main.c:687 |
| arch_call_rest_init+0x1c/0x28 |
| start_kernel+0x520/0x554 init/main.c:1064 |
| 0x0 |
| |
| Freed by task 270: |
| slab_free_hook mm/slub.c:1562 [inline] |
| slab_free_freelist_hook+0x98/0x260 mm/slub.c:1600 |
| slab_free mm/slub.c:3161 [inline] |
| kmem_cache_free+0x224/0x8e0 mm/slub.c:3177 |
| put_pid.part.4+0xe0/0x1a8 kernel/pid.c:114 |
| put_pid+0x30/0x48 kernel/pid.c:109 |
| proc_do_cad_pid+0x190/0x1b0 kernel/sysctl.c:1401 |
| proc_sys_call_handler+0x338/0x4b0 fs/proc/proc_sysctl.c:591 |
| proc_sys_write+0x34/0x48 fs/proc/proc_sysctl.c:617 |
| call_write_iter include/linux/fs.h:1977 [inline] |
| new_sync_write+0x3ac/0x510 fs/read_write.c:518 |
| vfs_write fs/read_write.c:605 [inline] |
| vfs_write+0x9c4/0x1018 fs/read_write.c:585 |
| ksys_write+0x124/0x240 fs/read_write.c:658 |
| __do_sys_write fs/read_write.c:670 [inline] |
| __se_sys_write fs/read_write.c:667 [inline] |
| __arm64_sys_write+0x78/0xb0 fs/read_write.c:667 |
| __invoke_syscall arch/arm64/kernel/syscall.c:37 [inline] |
| invoke_syscall arch/arm64/kernel/syscall.c:49 [inline] |
| el0_svc_common.constprop.1+0x16c/0x388 arch/arm64/kernel/syscall.c:129 |
| do_el0_svc+0xf8/0x150 arch/arm64/kernel/syscall.c:168 |
| el0_svc+0x28/0x38 arch/arm64/kernel/entry-common.c:416 |
| el0_sync_handler+0x134/0x180 arch/arm64/kernel/entry-common.c:432 |
| el0_sync+0x154/0x180 arch/arm64/kernel/entry.S:701 |
| |
| The buggy address belongs to the object at ffff23794dda0000 |
| which belongs to the cache pid of size 224 |
| The buggy address is located 4 bytes inside of |
| 224-byte region [ffff23794dda0000, ffff23794dda00e0) |
| The buggy address belongs to the page: |
| page:(____ptrval____) refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x4dda0 |
| head:(____ptrval____) order:1 compound_mapcount:0 |
| flags: 0x3fffc0000010200(slab|head) |
| raw: 03fffc0000010200 dead000000000100 dead000000000122 ffff23794d40d080 |
| raw: 0000000000000000 0000000000190019 00000001ffffffff 0000000000000000 |
| page dumped because: kasan: bad access detected |
| |
| Memory state around the buggy address: |
| ffff23794dd9ff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc |
| ffff23794dd9ff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc |
| >ffff23794dda0000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb |
| ^ |
| ffff23794dda0080: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc |
| ffff23794dda0100: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00 |
| ================================================================== |
| |
| Link: https://lkml.kernel.org/r/20210524172230.38715-1-mark.rutland@arm.com |
| Fixes: 9ec52099e4b8678a ("[PATCH] replace cad_pid by a struct pid") |
| Signed-off-by: Mark Rutland <mark.rutland@arm.com> |
| Acked-by: Christian Brauner <christian.brauner@ubuntu.com> |
| Cc: Cedric Le Goater <clg@fr.ibm.com> |
| Cc: Christian Brauner <christian@brauner.io> |
| Cc: Eric W. Biederman <ebiederm@xmission.com> |
| Cc: Kees Cook <keescook@chromium.org |
| Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> |
| Cc: Paul Mackerras <paulus@samba.org> |
| Cc: <stable@vger.kernel.org> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| init/main.c | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| --- a/init/main.c |
| +++ b/init/main.c |
| @@ -1505,7 +1505,7 @@ static noinline void __init kernel_init_ |
| */ |
| set_mems_allowed(node_states[N_MEMORY]); |
| |
| - cad_pid = task_pid(current); |
| + cad_pid = get_pid(task_pid(current)); |
| |
| smp_prepare_cpus(setup_max_cpus); |
| |
