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    Subject[PATCH 5.7 070/124] can: j1939: fix kernel-infoleak in j1939_sk_sock2sockaddr_can()
    Date
    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit 38ba8b9241f5848a49b80fddac9ab5f4692e434e ]

    syzbot found that at least 2 bytes of kernel information
    were leaked during getsockname() on AF_CAN CAN_J1939 socket.

    Since struct sockaddr_can has in fact two holes, simply
    clear the whole area before filling it with useful data.

    BUG: KMSAN: kernel-infoleak in kmsan_copy_to_user+0x81/0x90 mm/kmsan/kmsan_hooks.c:253
    CPU: 0 PID: 8466 Comm: syz-executor511 Not tainted 5.8.0-rc5-syzkaller #0
    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+0x21c/0x280 lib/dump_stack.c:118
    kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:121
    kmsan_internal_check_memory+0x238/0x3d0 mm/kmsan/kmsan.c:423
    kmsan_copy_to_user+0x81/0x90 mm/kmsan/kmsan_hooks.c:253
    instrument_copy_to_user include/linux/instrumented.h:91 [inline]
    _copy_to_user+0x18e/0x260 lib/usercopy.c:39
    copy_to_user include/linux/uaccess.h:186 [inline]
    move_addr_to_user+0x3de/0x670 net/socket.c:237
    __sys_getsockname+0x407/0x5e0 net/socket.c:1909
    __do_sys_getsockname net/socket.c:1920 [inline]
    __se_sys_getsockname+0x91/0xb0 net/socket.c:1917
    __x64_sys_getsockname+0x4a/0x70 net/socket.c:1917
    do_syscall_64+0xad/0x160 arch/x86/entry/common.c:386
    entry_SYSCALL_64_after_hwframe+0x44/0xa9
    RIP: 0033:0x440219
    Code: Bad RIP value.
    RSP: 002b:00007ffe5ee150c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000033
    RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440219
    RDX: 0000000020000240 RSI: 0000000020000100 RDI: 0000000000000003
    RBP: 00000000006ca018 R08: 0000000000000000 R09: 00000000004002c8
    R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401a20
    R13: 0000000000401ab0 R14: 0000000000000000 R15: 0000000000000000

    Local variable ----address@__sys_getsockname created at:
    __sys_getsockname+0x91/0x5e0 net/socket.c:1894
    __sys_getsockname+0x91/0x5e0 net/socket.c:1894

    Bytes 2-3 of 24 are uninitialized
    Memory access of size 24 starts at ffff8880ba2c7de8
    Data copied to user address 0000000020000100

    Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Reported-by: syzbot <syzkaller@googlegroups.com>
    Cc: Robin van der Gracht <robin@protonic.nl>
    Cc: Oleksij Rempel <o.rempel@pengutronix.de>
    Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
    Cc: linux-can@vger.kernel.org
    Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>
    Link: https://lore.kernel.org/r/20200813161834.4021638-1-edumazet@google.com
    Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/can/j1939/socket.c | 5 +++++
    1 file changed, 5 insertions(+)

    diff --git a/net/can/j1939/socket.c b/net/can/j1939/socket.c
    index 11d566c70a944..1b7dc1a8547f3 100644
    --- a/net/can/j1939/socket.c
    +++ b/net/can/j1939/socket.c
    @@ -561,6 +561,11 @@ static int j1939_sk_connect(struct socket *sock, struct sockaddr *uaddr,
    static void j1939_sk_sock2sockaddr_can(struct sockaddr_can *addr,
    const struct j1939_sock *jsk, int peer)
    {
    + /* There are two holes (2 bytes and 3 bytes) to clear to avoid
    + * leaking kernel information to user space.
    + */
    + memset(addr, 0, J1939_MIN_NAMELEN);
    +
    addr->can_family = AF_CAN;
    addr->can_ifindex = jsk->ifindex;
    addr->can_addr.j1939.pgn = jsk->addr.pgn;
    --
    2.25.1


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