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    Subject[PATCH 4.19 01/17] AX.25: Fix out-of-bounds read in ax25_connect()
    Date
    From: Peilin Ye <yepeilin.cs@gmail.com>

    [ Upstream commit 2f2a7ffad5c6cbf3d438e813cfdc88230e185ba6 ]

    Checks on `addr_len` and `fsa->fsa_ax25.sax25_ndigis` are insufficient.
    ax25_connect() can go out of bounds when `fsa->fsa_ax25.sax25_ndigis`
    equals to 7 or 8. Fix it.

    This issue has been reported as a KMSAN uninit-value bug, because in such
    a case, ax25_connect() reaches into the uninitialized portion of the
    `struct sockaddr_storage` statically allocated in __sys_connect().

    It is safe to remove `fsa->fsa_ax25.sax25_ndigis > AX25_MAX_DIGIS` because
    `addr_len` is guaranteed to be less than or equal to
    `sizeof(struct full_sockaddr_ax25)`.

    Reported-by: syzbot+c82752228ed975b0a623@syzkaller.appspotmail.com
    Link: https://syzkaller.appspot.com/bug?id=55ef9d629f3b3d7d70b69558015b63b48d01af66
    Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ax25/af_ax25.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    --- a/net/ax25/af_ax25.c
    +++ b/net/ax25/af_ax25.c
    @@ -1190,7 +1190,9 @@ static int __must_check ax25_connect(str
    if (addr_len > sizeof(struct sockaddr_ax25) &&
    fsa->fsa_ax25.sax25_ndigis != 0) {
    /* Valid number of digipeaters ? */
    - if (fsa->fsa_ax25.sax25_ndigis < 1 || fsa->fsa_ax25.sax25_ndigis > AX25_MAX_DIGIS) {
    + if (fsa->fsa_ax25.sax25_ndigis < 1 ||
    + addr_len < sizeof(struct sockaddr_ax25) +
    + sizeof(ax25_address) * fsa->fsa_ax25.sax25_ndigis) {
    err = -EINVAL;
    goto out_release;
    }

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