UPSTREAM: signal: use fdget() since we don't allow O_PATH

As stated in the oriGinal commit for pidfd_send_signal() we don't allow
to signal processes through O_PATH file descriptors since it is
semantically equivalent to a write on the pidfd.

We already correctly error out right now and return EBADF if an O_PATH
fd is passed.  This is because we use file->f_op to detect whether a
pidfd is passed and O_PATH fds have their file->f_op set to empty_fops
in do_dentry_open() and thus fail the test.

Thus, there is no regression.  It's just semantically correct to use
fdget() and return an error right from there instead of taking a
reference and returning an error later.

Signed-off-by: Christian Brauner <christian@brauner.io>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jann Horn <jann@thejh.net>
Cc: David Howells <dhowells@redhat.com>
Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Cc: Andy Lutomirsky <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 738a7832d21e3d911fcddab98ce260b79010b461)

Mot-CRs-fixed: (CR)

Bug: 135608568
Test: test program using syscall(__NR_pidfd_send_signal,..) to send SIGKILL
Change-Id: IMontanaeaadf9da371fb2d9caae4df49627760de7229
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-on: https://gerrit.mot.com/1505849
Tested-by: Jira Key
SLTApproved: Slta Waiver
SME-Granted: SME Approvals Granted
Reviewed-by: Wang Wang <wangwang1@mt.com>
Reviewed-by: Yonghui Jia <jiayh2@motorola.com>
Submit-Approved: Jira Key
Reviewed-on: https://gerrit.mot.com/1796157
Reviewed-by: Xiangpo Zhao <zhaoxp3@motorola.c

diff --git a/kernel/signal.c b/kernel/signal.c
index ee153e138b60704639d63b6c353aa64beac42ee5..3476b296fdb21f72527bfb222f31d2ac7e3162c3 100644 (file)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3116,7 +3116,7 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
        if (flags)
                return -EINVAL;
 
-       f = fdget_raw(pidfd);
+       f = fdget(pidfd);
        if (!f.file)
                return -EBADF;