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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Cedric Le Goater <clg@fr.ibm.com>,
	Christian Brauner <christian@brauner.io>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Paul Mackerras <paulus@samba.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH 4.9 21/29] pid: take a reference when initializing `cad_pid`
Date: Tue,  8 Jun 2021 20:27:15 +0200
Message-ID: <20210608175928.505394675@linuxfoundation.org> (raw)
In-Reply-To: <20210608175927.821075974@linuxfoundation.org>

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
@@ -1005,7 +1005,7 @@ static noinline void __init kernel_init_
 	 */
 	set_cpus_allowed_ptr(current, cpu_all_mask);
 
-	cad_pid = task_pid(current);
+	cad_pid = get_pid(task_pid(current));
 
 	smp_prepare_cpus(setup_max_cpus);
 



  parent reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-08 18:26 [PATCH 4.9 00/29] 4.9.272-rc1 review Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.9 01/29] net: usb: cdc_ncm: dont spew notifications Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.9 02/29] efi: Allow EFI_MEMORY_XP and EFI_MEMORY_RO both to be cleared Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.9 03/29] efi: cper: fix snprintf() use in cper_dimm_err_location() Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.9 04/29] vfio/pci: Fix error return code in vfio_ecap_init() Greg Kroah-Hartman
2021-06-08 18:26 ` [PATCH 4.9 05/29] vfio/pci: zap_vma_ptes() needs MMU Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 06/29] vfio/platform: fix module_put call in error flow Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 07/29] ipvs: ignore IP_VS_SVC_F_HASHED flag when adding service Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 08/29] HID: pidff: fix error return code in hid_pidff_init() Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 09/29] HID: i2c-hid: fix format string mismatch Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 10/29] netfilter: nfnetlink_cthelper: hit EBUSY on updates if size mismatches Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 11/29] ieee802154: fix error return code in ieee802154_add_iface() Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 12/29] ieee802154: fix error return code in ieee802154_llsec_getparams() Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 13/29] Bluetooth: fix the erroneous flush_work() order Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 14/29] Bluetooth: use correct lock to prevent UAF of hdev object Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 15/29] net: caif: added cfserl_release function Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 16/29] net: caif: add proper error handling Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 17/29] net: caif: fix memory leak in caif_device_notify Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 18/29] net: caif: fix memory leak in cfusbl_device_notify Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 19/29] ALSA: timer: Fix master timer notification Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 20/29] ext4: fix bug on in ext4_es_cache_extent as ext4_split_extent_at failed Greg Kroah-Hartman
2021-06-08 18:27 ` Greg Kroah-Hartman [this message]
2021-06-08 18:27 ` [PATCH 4.9 22/29] ocfs2: fix data corruption by fallocate Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 23/29] nfc: fix NULL ptr dereference in llcp_sock_getname() after failed connect Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 24/29] btrfs: fix error handling in btrfs_del_csums Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 25/29] btrfs: fixup error handling in fixup_inode_link_counts Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 26/29] bnxt_en: Remove the setting of dev_port Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 27/29] KVM: SVM: Truncate GPR value for DR and CR accesses in !64-bit mode Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 28/29] arm64: Remove unimplemented syscall log message Greg Kroah-Hartman
2021-06-08 18:27 ` [PATCH 4.9 29/29] xen-pciback: redo VF placement in the virtual topology Greg Kroah-Hartman
2021-06-09  2:55 ` [PATCH 4.9 00/29] 4.9.272-rc1 review Shuah Khan
2021-06-09  9:33 ` Jon Hunter
2021-06-09 11:53 ` Naresh Kamboju
2021-06-09 18:13 ` Florian Fainelli
2021-06-09 18:47 ` Guenter Roeck

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