Fix some typos in the psx.c code related to 6 argument syscalls.psx/v0.2.46-rc4

  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>

5 files changed, 39 insertions, 9 deletions

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")
+}
diff --git a/psx/psx.c b/psx/psx.c
index 74455b3..38251ed 100644
--- a/psx/psx.c
+++ b/psx/psx.c
@@ -220,8 +220,10 @@ static void psx_syscall_start(void) {
      * All sorts of things are assumed by Linux and glibc and/or musl
      * about signal handlers and which can be blocked. Go has its own
      * idiosyncrasies too. We tried SIGRTMAX until
-     * https://bugzilla.kernel.org/show_bug.cgi?id=210533, so this is
-     * our current strategy: to intercept SIGSYS.
+     *
+     *   https://bugzilla.kernel.org/show_bug.cgi?id=210533
+     *
+     * Our current strategy is to aggressively intercept SIGSYS.
      */
     psx_tracker.psx_sig = SIGSYS;
 
@@ -500,9 +502,9 @@ static long int __psx_immediate_syscall(long int syscall_nr,
 
     if (count > 3) {
 	psx_tracker.cmd.six = 1;
-	psx_tracker.cmd.arg1 = arg[3];
-	psx_tracker.cmd.arg2 = count > 4 ? arg[4] : 0;
-	psx_tracker.cmd.arg3 = count > 5 ? arg[5] : 0;
+	psx_tracker.cmd.arg4 = arg[3];
+	psx_tracker.cmd.arg5 = count > 4 ? arg[4] : 0;
+	psx_tracker.cmd.arg6 = count > 5 ? arg[5] : 0;
 	return syscall(syscall_nr,
 		      psx_tracker.cmd.arg1,
 		      psx_tracker.cmd.arg2,
@@ -559,7 +561,7 @@ long int __psx_syscall(long int syscall_nr, ...) {
 
     long int ret;
 
-    ret = __psx_immediate_syscall(syscall_nr, count, arg);;
+    ret = __psx_immediate_syscall(syscall_nr, count, arg);
     if (ret == -1 || !psx_tracker.initialized) {
 	psx_new_state(_PSX_SETUP, _PSX_IDLE);
 	goto defer;
diff --git a/psx/psx_syscall.h b/psx/psx_syscall.h
index 4c99375..4aacfab 100644
--- a/psx/psx_syscall.h
+++ b/psx/psx_syscall.h
@@ -43,7 +43,9 @@ extern "C" {
  * and psx_syscall6().
  */
 #define psx_syscall(syscall_nr, ...) \
-    __psx_syscall(syscall_nr, __VA_ARGS__, 6, 5, 4, 3, 2, 1, 0)
+    __psx_syscall(syscall_nr, __VA_ARGS__, (long int) 6, (long int) 5, \
+		  (long int) 4, (long int) 3, (long int) 2, \
+		  (long int) 1, (long int) 0)
 long int __psx_syscall(long int syscall_nr, ...);
 long int psx_syscall3(long int syscall_nr,
 		      long int arg1, long int arg2, long int arg3);