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    Subject[PATCH 3.2 174/199] sock: fix sendmmsg for partial sendmsg
    3.2.87-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Soheil Hassas Yeganeh <soheil@google.com>

    [ Upstream commit 3023898b7d4aac65987bd2f485cc22390aae6f78 ]

    Do not send the next message in sendmmsg for partial sendmsg
    invocations.

    sendmmsg assumes that it can continue sending the next message
    when the return value of the individual sendmsg invocations
    is positive. It results in corrupting the data for TCP,
    SCTP, and UNIX streams.

    For example, sendmmsg([["abcd"], ["efgh"]]) can result in a stream
    of "aefgh" if the first sendmsg invocation sends only the first
    byte while the second sendmsg goes through.

    Datagram sockets either send the entire datagram or fail, so
    this patch affects only sockets of type SOCK_STREAM and
    SOCK_SEQPACKET.

    Fixes: 228e548e6020 ("net: Add sendmmsg socket system call")
    Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Signed-off-by: Willem de Bruijn <willemb@google.com>
    Signed-off-by: Neal Cardwell <ncardwell@google.com>
    Acked-by: Maciej Żenczykowski <maze@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    [bwh: Backported to 3.2: we don't have the iov_iter API, so make
    ___sys_sendmsg() calculate and write back the remaining length]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    net/socket.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/net/socket.c
    +++ b/net/socket.c
    @@ -1898,7 +1898,7 @@ static int copy_msghdr_from_user(struct

    static int ___sys_sendmsg(struct socket *sock, struct msghdr __user *msg,
    struct msghdr *msg_sys, unsigned flags,
    - struct used_address *used_address)
    + struct used_address *used_address, int *residue)
    {
    struct compat_msghdr __user *msg_compat =
    (struct compat_msghdr __user *)msg;
    @@ -2004,6 +2004,8 @@ static int ___sys_sendmsg(struct socket
    memcpy(&used_address->name, msg_sys->msg_name,
    used_address->name_len);
    }
    + if (residue && err >= 0)
    + *residue = total_len - err;

    out_freectl:
    if (ctl_buf != ctl)
    @@ -2029,7 +2031,7 @@ long __sys_sendmsg(int fd, struct msghdr
    if (!sock)
    goto out;

    - err = ___sys_sendmsg(sock, msg, &msg_sys, flags, NULL);
    + err = ___sys_sendmsg(sock, msg, &msg_sys, flags, NULL, NULL);

    fput_light(sock->file, fput_needed);
    out:
    @@ -2056,6 +2058,7 @@ int __sys_sendmmsg(int fd, struct mmsghd
    struct compat_mmsghdr __user *compat_entry;
    struct msghdr msg_sys;
    struct used_address used_address;
    + int residue;

    if (vlen > UIO_MAXIOV)
    vlen = UIO_MAXIOV;
    @@ -2074,7 +2077,8 @@ int __sys_sendmmsg(int fd, struct mmsghd
    while (datagrams < vlen) {
    if (MSG_CMSG_COMPAT & flags) {
    err = ___sys_sendmsg(sock, (struct msghdr __user *)compat_entry,
    - &msg_sys, flags, &used_address);
    + &msg_sys, flags, &used_address,
    + &residue);
    if (err < 0)
    break;
    err = __put_user(err, &compat_entry->msg_len);
    @@ -2082,7 +2086,8 @@ int __sys_sendmmsg(int fd, struct mmsghd
    } else {
    err = ___sys_sendmsg(sock,
    (struct msghdr __user *)entry,
    - &msg_sys, flags, &used_address);
    + &msg_sys, flags, &used_address,
    + &residue);
    if (err < 0)
    break;
    err = put_user(err, &entry->msg_len);
    @@ -2092,6 +2097,8 @@ int __sys_sendmmsg(int fd, struct mmsghd
    if (err)
    break;
    ++datagrams;
    + if (residue)
    + break;
    }

    fput_light(sock->file, fput_needed);
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