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    Subject[07/23] Prevent rt_sigqueueinfo and rt_tgsigqueueinfo from spoofing the signal code
    From: Julien Tinnes <jln@google.com>

    commit da48524eb20662618854bb3df2db01fc65f3070c upstream.

    Userland should be able to trust the pid and uid of the sender of a
    signal if the si_code is SI_TKILL.

    Unfortunately, the kernel has historically allowed sigqueueinfo() to
    send any si_code at all (as long as it was negative - to distinguish it
    from kernel-generated signals like SIGILL etc), so it could spoof a
    SI_TKILL with incorrect siginfo values.

    Happily, it looks like glibc has always set si_code to the appropriate
    SI_QUEUE, so there are probably no actual user code that ever uses
    anything but the appropriate SI_QUEUE flag.

    So just tighten the check for si_code (we used to allow any negative
    value), and add a (one-time) warning in case there are binaries out
    there that might depend on using other si_code values.

    Signed-off-by: Julien Tinnes <jln@google.com>
    Acked-by: Oleg Nesterov <oleg@redhat.com>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    kernel/signal.c | 16 ++++++++++++----
    1 file changed, 12 insertions(+), 4 deletions(-)

    --- a/kernel/signal.c
    +++ b/kernel/signal.c
    @@ -2351,9 +2351,13 @@ SYSCALL_DEFINE3(rt_sigqueueinfo, pid_t,
    return -EFAULT;

    /* Not even root can pretend to send signals from the kernel.
    - Nor can they impersonate a kill(), which adds source info. */
    - if (info.si_code >= 0)
    + * Nor can they impersonate a kill()/tgkill(), which adds source info.
    + */
    + if (info.si_code != SI_QUEUE) {
    + /* We used to allow any < 0 si_code */
    + WARN_ON_ONCE(info.si_code < 0);
    return -EPERM;
    + }
    info.si_signo = sig;

    /* POSIX.1b doesn't mention process groups. */
    @@ -2367,9 +2371,13 @@ long do_rt_tgsigqueueinfo(pid_t tgid, pi
    return -EINVAL;

    /* Not even root can pretend to send signals from the kernel.
    - Nor can they impersonate a kill(), which adds source info. */
    - if (info->si_code >= 0)
    + * Nor can they impersonate a kill()/tgkill(), which adds source info.
    + */
    + if (info->si_code != SI_QUEUE) {
    + /* We used to allow any < 0 si_code */
    + WARN_ON_ONCE(info->si_code < 0);
    return -EPERM;
    + }
    info->si_signo = sig;

    return do_send_specific(tgid, pid, sig, info);



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