From e7e0e1b9e2cf3378d329174ed5b0c716b0539c72 Mon Sep 17 00:00:00 2001
From: "Andrew G. Morgan" <morgan@kernel.org>
Date: Thu, 10 Dec 2020 21:58:10 -0800
Subject: Fix some typos in the psx.c code related to 6 argument syscalls.

  https://bugzilla.kernel.org/show_bug.cgi?id=210613

Essentially, 6 argument psx_syscall()s were not correctly implemented
before. The only consumer of these in [lib]cap were to set and reset
the ambient capability values, and so far I evidently hadn't tested
them in a multithreaded program.

Six argument psx_syscall()s work now, and I've adapted the reproducer
code into a new make sudotest.

Also cleaned up the psx_syscall() macro to remove any ambiguity about
argument sizes.

Signed-off-by: Andrew G. Morgan <morgan@kernel.org>
---
 go/.gitignore |  1 +
 go/Makefile   |  8 ++++++--
 go/b210613.go | 21 +++++++++++++++++++++
 3 files changed, 28 insertions(+), 2 deletions(-)
 create mode 100644 go/b210613.go

(limited to 'go')

diff --git a/go/.gitignore b/go/.gitignore
index 461bb4d..30ae0b6 100644
--- a/go/.gitignore
+++ b/go/.gitignore
@@ -3,6 +3,7 @@ compare-cap
 try-launching
 try-launching-cgo
 psx-signals
+b210613
 mknames
 web
 setid
diff --git a/go/Makefile b/go/Makefile
index b22a9bc..3bd79c8 100644
--- a/go/Makefile
+++ b/go/Makefile
@@ -80,6 +80,9 @@ endif
 psx-signals: psx-signals.go  $(PSXGOPACKAGE)
 	GO111MODULE=off CGO_LDFLAGS_ALLOW="$(CGO_LDFLAGS_ALLOW)" CGO_CFLAGS="$(CGO_CFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" GOPATH=$(GOPATH) $(GO) build $<
 
+b210613: b210613.go $(CAPGOPACKAGE)
+	GO111MODULE=off CGO_LDFLAGS_ALLOW="$(CGO_LDFLAGS_ALLOW)" CGO_CFLAGS="$(CGO_CFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" GOPATH=$(GOPATH) $(GO) build $<
+
 test: all
 	GO111MODULE=off CGO_LDFLAGS_ALLOW="$(CGO_LDFLAGS_ALLOW)" GOPATH="$(GOPATH)" $(GO) test $(IMPORTDIR)/psx
 	GO111MODULE=off CGO_LDFLAGS_ALLOW="$(CGO_LDFLAGS_ALLOW)" GOPATH="$(GOPATH)" $(GO) test $(IMPORTDIR)/cap
@@ -91,7 +94,7 @@ test: all
 # Note, the user namespace doesn't require sudo, but I wanted to avoid
 # requiring that the hosting kernel supports user namespaces for the
 # regular test case.
-sudotest: test ../progs/tcapsh-static
+sudotest: test ../progs/tcapsh-static b210613
 	./gowns --ns -- -c "echo gowns runs with user namespace"
 	./try-launching
 ifeq ($(CGO_REQUIRED),0)
@@ -101,6 +104,7 @@ endif
 ifeq ($(CGO_REQUIRED),0)
 	sudo ./try-launching-cgo
 endif
+	sudo ../progs/tcapsh-static --cap-uid=$$(id -u) --caps="cap_setpcap=ep" --iab="^cap_setpcap" -- -c ./b210613
 
 install: all
 	rm -rf $(FAKEROOT)$(GOPKGDIR)/$(IMPORTDIR)/psx
@@ -115,5 +119,5 @@ clean:
 	rm -f web setid gowns
 	rm -f compare-cap try-launching try-launching-cgo
 	rm -f $(topdir)/cap/*~ $(topdir)/psx/*~
-	rm -f psx-signals
+	rm -f psx-signals b210613
 	rm -fr pkg src
diff --git a/go/b210613.go b/go/b210613.go
new file mode 100644
index 0000000..2bced06
--- /dev/null
+++ b/go/b210613.go
@@ -0,0 +1,21 @@
+// Program b210613 reproduces the code reported in:
+//
+//  https://bugzilla.kernel.org/show_bug.cgi?id=210613
+//
+// This file is evolved directly from the reproducer attached to that
+// bug report originally authored by Lorenz Bauer.
+package main
+
+import (
+	"fmt"
+	"log"
+
+	"kernel.org/pub/linux/libs/security/libcap/cap"
+)
+
+func main() {
+	if err := cap.ModeNoPriv.Set(); err != nil {
+		log.Fatalf("error dropping privilege: %v", err)
+	}
+	fmt.Println("b210613: PASSED")
+}
-- 
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