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    Subject[PATCH AUTOSEL 4.20 59/77] ax25: fix possible use-after-free
    Date
    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit 63530aba7826a0f8e129874df9c4d264f9db3f9e ]

    syzbot found that ax25 routes where not properly protected
    against concurrent use [1].

    In this particular report the bug happened while
    copying ax25->digipeat.

    Fix this problem by making sure we call ax25_get_route()
    while ax25_route_lock is held, so that no modification
    could happen while using the route.

    The current two ax25_get_route() callers do not sleep,
    so this change should be fine.

    Once we do that, ax25_get_route() no longer needs to
    grab a reference on the found route.

    [1]
    ax25_connect(): syz-executor0 uses autobind, please contact jreuter@yaina.de
    BUG: KASAN: use-after-free in memcpy include/linux/string.h:352 [inline]
    BUG: KASAN: use-after-free in kmemdup+0x42/0x60 mm/util.c:113
    Read of size 66 at addr ffff888066641a80 by task syz-executor2/531

    ax25_connect(): syz-executor0 uses autobind, please contact jreuter@yaina.de
    CPU: 1 PID: 531 Comm: syz-executor2 Not tainted 5.0.0-rc2+ #10
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
    Call Trace:
    __dump_stack lib/dump_stack.c:77 [inline]
    dump_stack+0x1db/0x2d0 lib/dump_stack.c:113
    print_address_description.cold+0x7c/0x20d mm/kasan/report.c:187
    kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
    check_memory_region_inline mm/kasan/generic.c:185 [inline]
    check_memory_region+0x123/0x190 mm/kasan/generic.c:191
    memcpy+0x24/0x50 mm/kasan/common.c:130
    memcpy include/linux/string.h:352 [inline]
    kmemdup+0x42/0x60 mm/util.c:113
    kmemdup include/linux/string.h:425 [inline]
    ax25_rt_autobind+0x25d/0x750 net/ax25/ax25_route.c:424
    ax25_connect.cold+0x30/0xa4 net/ax25/af_ax25.c:1224
    __sys_connect+0x357/0x490 net/socket.c:1664
    __do_sys_connect net/socket.c:1675 [inline]
    __se_sys_connect net/socket.c:1672 [inline]
    __x64_sys_connect+0x73/0xb0 net/socket.c:1672
    do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
    entry_SYSCALL_64_after_hwframe+0x49/0xbe
    RIP: 0033:0x458099
    Code: 6d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 3b b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
    RSP: 002b:00007f870ee22c78 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
    RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000458099
    RDX: 0000000000000048 RSI: 0000000020000080 RDI: 0000000000000005
    RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
    ax25_connect(): syz-executor4 uses autobind, please contact jreuter@yaina.de
    R10: 0000000000000000 R11: 0000000000000246 R12: 00007f870ee236d4
    R13: 00000000004be48e R14: 00000000004ce9a8 R15: 00000000ffffffff

    Allocated by task 526:
    save_stack+0x45/0xd0 mm/kasan/common.c:73
    set_track mm/kasan/common.c:85 [inline]
    __kasan_kmalloc mm/kasan/common.c:496 [inline]
    __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:469
    kasan_kmalloc+0x9/0x10 mm/kasan/common.c:504
    ax25_connect(): syz-executor5 uses autobind, please contact jreuter@yaina.de
    kmem_cache_alloc_trace+0x151/0x760 mm/slab.c:3609
    kmalloc include/linux/slab.h:545 [inline]
    ax25_rt_add net/ax25/ax25_route.c:95 [inline]
    ax25_rt_ioctl+0x3b9/0x1270 net/ax25/ax25_route.c:233
    ax25_ioctl+0x322/0x10b0 net/ax25/af_ax25.c:1763
    sock_do_ioctl+0xe2/0x400 net/socket.c:950
    sock_ioctl+0x32f/0x6c0 net/socket.c:1074
    vfs_ioctl fs/ioctl.c:46 [inline]
    file_ioctl fs/ioctl.c:509 [inline]
    do_vfs_ioctl+0x107b/0x17d0 fs/ioctl.c:696
    ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
    __do_sys_ioctl fs/ioctl.c:720 [inline]
    __se_sys_ioctl fs/ioctl.c:718 [inline]
    __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
    do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
    entry_SYSCALL_64_after_hwframe+0x49/0xbe

    ax25_connect(): syz-executor5 uses autobind, please contact jreuter@yaina.de
    Freed by task 550:
    save_stack+0x45/0xd0 mm/kasan/common.c:73
    set_track mm/kasan/common.c:85 [inline]
    __kasan_slab_free+0x102/0x150 mm/kasan/common.c:458
    kasan_slab_free+0xe/0x10 mm/kasan/common.c:466
    __cache_free mm/slab.c:3487 [inline]
    kfree+0xcf/0x230 mm/slab.c:3806
    ax25_rt_add net/ax25/ax25_route.c:92 [inline]
    ax25_rt_ioctl+0x304/0x1270 net/ax25/ax25_route.c:233
    ax25_ioctl+0x322/0x10b0 net/ax25/af_ax25.c:1763
    sock_do_ioctl+0xe2/0x400 net/socket.c:950
    sock_ioctl+0x32f/0x6c0 net/socket.c:1074
    vfs_ioctl fs/ioctl.c:46 [inline]
    file_ioctl fs/ioctl.c:509 [inline]
    do_vfs_ioctl+0x107b/0x17d0 fs/ioctl.c:696
    ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
    __do_sys_ioctl fs/ioctl.c:720 [inline]
    __se_sys_ioctl fs/ioctl.c:718 [inline]
    __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
    do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
    entry_SYSCALL_64_after_hwframe+0x49/0xbe

    The buggy address belongs to the object at ffff888066641a80
    which belongs to the cache kmalloc-96 of size 96
    The buggy address is located 0 bytes inside of
    96-byte region [ffff888066641a80, ffff888066641ae0)
    The buggy address belongs to the page:
    page:ffffea0001999040 count:1 mapcount:0 mapping:ffff88812c3f04c0 index:0x0
    flags: 0x1fffc0000000200(slab)
    ax25_connect(): syz-executor4 uses autobind, please contact jreuter@yaina.de
    raw: 01fffc0000000200 ffffea0001817948 ffffea0002341dc8 ffff88812c3f04c0
    raw: 0000000000000000 ffff888066641000 0000000100000020 0000000000000000
    page dumped because: kasan: bad access detected

    Memory state around the buggy address:
    ffff888066641980: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
    ffff888066641a00: 00 00 00 00 00 00 00 00 02 fc fc fc fc fc fc fc
    >ffff888066641a80: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
    ^
    ffff888066641b00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
    ffff888066641b80: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc

    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Cc: Ralf Baechle <ralf@linux-mips.org>
    Reported-by: syzbot <syzkaller@googlegroups.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    include/net/ax25.h | 12 ++++++++++++
    net/ax25/ax25_ip.c | 4 ++--
    net/ax25/ax25_route.c | 19 ++++++++-----------
    3 files changed, 22 insertions(+), 13 deletions(-)

    diff --git a/include/net/ax25.h b/include/net/ax25.h
    index 3f9aea8087e3..8b7eb46ad72d 100644
    --- a/include/net/ax25.h
    +++ b/include/net/ax25.h
    @@ -201,6 +201,18 @@ static inline void ax25_hold_route(ax25_route *ax25_rt)

    void __ax25_put_route(ax25_route *ax25_rt);

    +extern rwlock_t ax25_route_lock;
    +
    +static inline void ax25_route_lock_use(void)
    +{
    + read_lock(&ax25_route_lock);
    +}
    +
    +static inline void ax25_route_lock_unuse(void)
    +{
    + read_unlock(&ax25_route_lock);
    +}
    +
    static inline void ax25_put_route(ax25_route *ax25_rt)
    {
    if (refcount_dec_and_test(&ax25_rt->refcount))
    diff --git a/net/ax25/ax25_ip.c b/net/ax25/ax25_ip.c
    index 70417e9b932d..314bbc8010fb 100644
    --- a/net/ax25/ax25_ip.c
    +++ b/net/ax25/ax25_ip.c
    @@ -114,6 +114,7 @@ netdev_tx_t ax25_ip_xmit(struct sk_buff *skb)
    dst = (ax25_address *)(bp + 1);
    src = (ax25_address *)(bp + 8);

    + ax25_route_lock_use();
    route = ax25_get_route(dst, NULL);
    if (route) {
    digipeat = route->digipeat;
    @@ -206,9 +207,8 @@ netdev_tx_t ax25_ip_xmit(struct sk_buff *skb)
    ax25_queue_xmit(skb, dev);

    put:
    - if (route)
    - ax25_put_route(route);

    + ax25_route_lock_unuse();
    return NETDEV_TX_OK;
    }

    diff --git a/net/ax25/ax25_route.c b/net/ax25/ax25_route.c
    index a0eff323af12..66f74c85cf6b 100644
    --- a/net/ax25/ax25_route.c
    +++ b/net/ax25/ax25_route.c
    @@ -40,7 +40,7 @@
    #include <linux/export.h>

    static ax25_route *ax25_route_list;
    -static DEFINE_RWLOCK(ax25_route_lock);
    +DEFINE_RWLOCK(ax25_route_lock);

    void ax25_rt_device_down(struct net_device *dev)
    {
    @@ -335,6 +335,7 @@ const struct seq_operations ax25_rt_seqops = {
    * Find AX.25 route
    *
    * Only routes with a reference count of zero can be destroyed.
    + * Must be called with ax25_route_lock read locked.
    */
    ax25_route *ax25_get_route(ax25_address *addr, struct net_device *dev)
    {
    @@ -342,7 +343,6 @@ ax25_route *ax25_get_route(ax25_address *addr, struct net_device *dev)
    ax25_route *ax25_def_rt = NULL;
    ax25_route *ax25_rt;

    - read_lock(&ax25_route_lock);
    /*
    * Bind to the physical interface we heard them on, or the default
    * route if none is found;
    @@ -365,11 +365,6 @@ ax25_route *ax25_get_route(ax25_address *addr, struct net_device *dev)
    if (ax25_spe_rt != NULL)
    ax25_rt = ax25_spe_rt;

    - if (ax25_rt != NULL)
    - ax25_hold_route(ax25_rt);
    -
    - read_unlock(&ax25_route_lock);
    -
    return ax25_rt;
    }

    @@ -400,9 +395,12 @@ int ax25_rt_autobind(ax25_cb *ax25, ax25_address *addr)
    ax25_route *ax25_rt;
    int err = 0;

    - if ((ax25_rt = ax25_get_route(addr, NULL)) == NULL)
    + ax25_route_lock_use();
    + ax25_rt = ax25_get_route(addr, NULL);
    + if (!ax25_rt) {
    + ax25_route_lock_unuse();
    return -EHOSTUNREACH;
    -
    + }
    if ((ax25->ax25_dev = ax25_dev_ax25dev(ax25_rt->dev)) == NULL) {
    err = -EHOSTUNREACH;
    goto put;
    @@ -437,8 +435,7 @@ int ax25_rt_autobind(ax25_cb *ax25, ax25_address *addr)
    }

    put:
    - ax25_put_route(ax25_rt);
    -
    + ax25_route_lock_unuse();
    return err;
    }

    --
    2.19.1
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