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    Subject[PATCH 5.13 056/127] net: 6pack: fix slab-out-of-bounds in decode_data
    Date
    From: Pavel Skripkin <paskripkin@gmail.com>

    [ Upstream commit 19d1532a187669ce86d5a2696eb7275310070793 ]

    Syzbot reported slab-out-of bounds write in decode_data().
    The problem was in missing validation checks.

    Syzbot's reproducer generated malicious input, which caused
    decode_data() to be called a lot in sixpack_decode(). Since
    rx_count_cooked is only 400 bytes and noone reported before,
    that 400 bytes is not enough, let's just check if input is malicious
    and complain about buffer overrun.

    Fail log:
    ==================================================================
    BUG: KASAN: slab-out-of-bounds in drivers/net/hamradio/6pack.c:843
    Write of size 1 at addr ffff888087c5544e by task kworker/u4:0/7

    CPU: 0 PID: 7 Comm: kworker/u4:0 Not tainted 5.6.0-rc3-syzkaller #0
    ...
    Workqueue: events_unbound flush_to_ldisc
    Call Trace:
    __dump_stack lib/dump_stack.c:77 [inline]
    dump_stack+0x197/0x210 lib/dump_stack.c:118
    print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
    __kasan_report.cold+0x1b/0x32 mm/kasan/report.c:506
    kasan_report+0x12/0x20 mm/kasan/common.c:641
    __asan_report_store1_noabort+0x17/0x20 mm/kasan/generic_report.c:137
    decode_data.part.0+0x23b/0x270 drivers/net/hamradio/6pack.c:843
    decode_data drivers/net/hamradio/6pack.c:965 [inline]
    sixpack_decode drivers/net/hamradio/6pack.c:968 [inline]

    Reported-and-tested-by: syzbot+fc8cd9a673d4577fb2e4@syzkaller.appspotmail.com
    Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
    Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
    Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/net/hamradio/6pack.c | 6 ++++++
    1 file changed, 6 insertions(+)

    diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c
    index 80f41945709f..da6a2a4b6cc7 100644
    --- a/drivers/net/hamradio/6pack.c
    +++ b/drivers/net/hamradio/6pack.c
    @@ -833,6 +833,12 @@ static void decode_data(struct sixpack *sp, unsigned char inbyte)
    return;
    }

    + if (sp->rx_count_cooked + 2 >= sizeof(sp->cooked_buf)) {
    + pr_err("6pack: cooked buffer overrun, data loss\n");
    + sp->rx_count = 0;
    + return;
    + }
    +
    buf = sp->raw_buf;
    sp->cooked_buf[sp->rx_count_cooked++] =
    buf[0] | ((buf[1] << 2) & 0xc0);
    --
    2.30.2
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