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    Subject[PATCH 4.15 29/72] net: xfrm: use preempt-safe this_cpu_read() in ipcomp_alloc_tfms()
    Date
    4.15-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Greg Hackmann <ghackmann@google.com>

    commit 0dcd7876029b58770f769cbb7b484e88e4a305e5 upstream.

    f7c83bcbfaf5 ("net: xfrm: use __this_cpu_read per-cpu helper") added a
    __this_cpu_read() call inside ipcomp_alloc_tfms().

    At the time, __this_cpu_read() required the caller to either not care
    about races or to handle preemption/interrupt issues. 3.15 tightened
    the rules around some per-cpu operations, and now __this_cpu_read()
    should never be used in a preemptible context. On 3.15 and later, we
    need to use this_cpu_read() instead.

    syzkaller reported this leading to the following kernel BUG while
    fuzzing sendmsg:

    BUG: using __this_cpu_read() in preemptible [00000000] code: repro/3101
    caller is ipcomp_init_state+0x185/0x990
    CPU: 3 PID: 3101 Comm: repro Not tainted 4.16.0-rc4-00123-g86f84779d8e9 #154
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
    Call Trace:
    dump_stack+0xb9/0x115
    check_preemption_disabled+0x1cb/0x1f0
    ipcomp_init_state+0x185/0x990
    ? __xfrm_init_state+0x876/0xc20
    ? lock_downgrade+0x5e0/0x5e0
    ipcomp4_init_state+0xaa/0x7c0
    __xfrm_init_state+0x3eb/0xc20
    xfrm_init_state+0x19/0x60
    pfkey_add+0x20df/0x36f0
    ? pfkey_broadcast+0x3dd/0x600
    ? pfkey_sock_destruct+0x340/0x340
    ? pfkey_seq_stop+0x80/0x80
    ? __skb_clone+0x236/0x750
    ? kmem_cache_alloc+0x1f6/0x260
    ? pfkey_sock_destruct+0x340/0x340
    ? pfkey_process+0x62a/0x6f0
    pfkey_process+0x62a/0x6f0
    ? pfkey_send_new_mapping+0x11c0/0x11c0
    ? mutex_lock_io_nested+0x1390/0x1390
    pfkey_sendmsg+0x383/0x750
    ? dump_sp+0x430/0x430
    sock_sendmsg+0xc0/0x100
    ___sys_sendmsg+0x6c8/0x8b0
    ? copy_msghdr_from_user+0x3b0/0x3b0
    ? pagevec_lru_move_fn+0x144/0x1f0
    ? find_held_lock+0x32/0x1c0
    ? do_huge_pmd_anonymous_page+0xc43/0x11e0
    ? lock_downgrade+0x5e0/0x5e0
    ? get_kernel_page+0xb0/0xb0
    ? _raw_spin_unlock+0x29/0x40
    ? do_huge_pmd_anonymous_page+0x400/0x11e0
    ? __handle_mm_fault+0x553/0x2460
    ? __fget_light+0x163/0x1f0
    ? __sys_sendmsg+0xc7/0x170
    __sys_sendmsg+0xc7/0x170
    ? SyS_shutdown+0x1a0/0x1a0
    ? __do_page_fault+0x5a0/0xca0
    ? lock_downgrade+0x5e0/0x5e0
    SyS_sendmsg+0x27/0x40
    ? __sys_sendmsg+0x170/0x170
    do_syscall_64+0x19f/0x640
    entry_SYSCALL_64_after_hwframe+0x42/0xb7
    RIP: 0033:0x7f0ee73dfb79
    RSP: 002b:00007ffe14fc15a8 EFLAGS: 00000207 ORIG_RAX: 000000000000002e
    RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f0ee73dfb79
    RDX: 0000000000000000 RSI: 00000000208befc8 RDI: 0000000000000004
    RBP: 00007ffe14fc15b0 R08: 00007ffe14fc15c0 R09: 00007ffe14fc15c0
    R10: 0000000000000000 R11: 0000000000000207 R12: 0000000000400440
    R13: 00007ffe14fc16b0 R14: 0000000000000000 R15: 0000000000000000

    Signed-off-by: Greg Hackmann <ghackmann@google.com>
    Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    net/xfrm/xfrm_ipcomp.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/net/xfrm/xfrm_ipcomp.c
    +++ b/net/xfrm/xfrm_ipcomp.c
    @@ -283,7 +283,7 @@ static struct crypto_comp * __percpu *ip
    struct crypto_comp *tfm;

    /* This can be any valid CPU ID so we don't need locking. */
    - tfm = __this_cpu_read(*pos->tfms);
    + tfm = this_cpu_read(*pos->tfms);

    if (!strcmp(crypto_comp_name(tfm), alg_name)) {
    pos->users++;

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