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    Subject[PATCH 5.17 716/772] um: chan_user: Fix winch_tramp() return value
    Date
    From: Johannes Berg <johannes.berg@intel.com>

    commit 57ae0b67b747031bc41fb44643aa5344ab58607e upstream.

    The previous fix here was only partially correct, it did
    result in returning a proper error value in case of error,
    but it also clobbered the pid that we need to return from
    this function (not just zero for success).

    As a result, it returned 0 here, but later this is treated
    as a pid and used to kill the process, but since it's now
    0 we kill(0, SIGKILL), which makes UML kill itself rather
    than just the helper thread.

    Fix that and make it more obvious by using a separate
    variable for the pid.

    Fixes: ccf1236ecac4 ("um: fix error return code in winch_tramp()")
    Reported-and-tested-by: Nathan Chancellor <nathan@kernel.org>
    Signed-off-by: Johannes Berg <johannes.berg@intel.com>
    Cc: stable@vger.kernel.org
    Signed-off-by: Richard Weinberger <richard@nod.at>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/um/drivers/chan_user.c | 9 +++++----
    1 file changed, 5 insertions(+), 4 deletions(-)

    --- a/arch/um/drivers/chan_user.c
    +++ b/arch/um/drivers/chan_user.c
    @@ -220,7 +220,7 @@ static int winch_tramp(int fd, struct tt
    unsigned long *stack_out)
    {
    struct winch_data data;
    - int fds[2], n, err;
    + int fds[2], n, err, pid;
    char c;

    err = os_pipe(fds, 1, 1);
    @@ -238,8 +238,9 @@ static int winch_tramp(int fd, struct tt
    * problem with /dev/net/tun, which if held open by this
    * thread, prevents the TUN/TAP device from being reused.
    */
    - err = run_helper_thread(winch_thread, &data, CLONE_FILES, stack_out);
    - if (err < 0) {
    + pid = run_helper_thread(winch_thread, &data, CLONE_FILES, stack_out);
    + if (pid < 0) {
    + err = pid;
    printk(UM_KERN_ERR "fork of winch_thread failed - errno = %d\n",
    -err);
    goto out_close;
    @@ -263,7 +264,7 @@ static int winch_tramp(int fd, struct tt
    goto out_close;
    }

    - return err;
    + return pid;

    out_close:
    close(fds[1]);

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