[LTP] [PATCH v3 2/2] syscalls/cma: Handle Yama ptrace_scope in tests

[Andrea Cervesato <andrea.cervesato@suse.de>]

From: Andrea Cervesato <andrea.cervesato@suse.com>

With Yama LSM enabled, process_vm_readv() and process_vm_writev() fail
with EPERM when a sibling process accesses the target's memory.

Let the target child declare its parent as ptracer, so that mode 1
works for unprivileged users too. Require CAP_SYS_PTRACE for mode 2
and skip on mode 3, where access is never allowed.

Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
---
 testcases/kernel/syscalls/cma/cma.h                | 38 ++++++++++++++++++++++
 testcases/kernel/syscalls/cma/process_vm_readv02.c |  5 +++
 testcases/kernel/syscalls/cma/process_vm_readv03.c |  5 +++
 .../kernel/syscalls/cma/process_vm_writev02.c      |  5 +++
 4 files changed, 53 insertions(+)

diff --git a/testcases/kernel/syscalls/cma/cma.h b/testcases/kernel/syscalls/cma/cma.h
new file mode 100644
index 000000000..6636cb5a3
--- /dev/null
+++ b/testcases/kernel/syscalls/cma/cma.h
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2026 SUSE LLC Andrea Cervesato <andrea.cervesato@suse.com>
+ */
+
+#ifndef CMA_H__
+#define CMA_H__
+
+#include <sys/prctl.h>
+#include "tst_test.h"
+#include "tst_capability.h"
+
+#define PTRACE_SCOPE "/proc/sys/kernel/yama/ptrace_scope"
+
+static inline void cma_check_ptrace_scope(void)
+{
+	struct tst_cap cap = TST_CAP(TST_CAP_REQ, CAP_SYS_PTRACE);
+	int scope;
+
+	if (access(PTRACE_SCOPE, F_OK))
+		return;
+
+	SAFE_FILE_SCANF(PTRACE_SCOPE, "%d", &scope);
+
+	if (scope >= 3)
+		tst_brk(TCONF, "Yama ptrace_scope=%d forbids process_vm_*()", scope);
+
+	if (scope == 2)
+		tst_cap_action(&cap);
+}
+
+static inline void cma_allow_parent_ptracer(void)
+{
+	if (prctl(PR_SET_PTRACER, getppid(), 0, 0, 0) && errno != EINVAL)
+		tst_brk(TBROK | TERRNO, "prctl(PR_SET_PTRACER)");
+}
+
+#endif /* CMA_H__ */
diff --git a/testcases/kernel/syscalls/cma/process_vm_readv02.c b/testcases/kernel/syscalls/cma/process_vm_readv02.c
index 1e2ac38fa..ceff77e29 100644
--- a/testcases/kernel/syscalls/cma/process_vm_readv02.c
+++ b/testcases/kernel/syscalls/cma/process_vm_readv02.c
@@ -17,6 +17,7 @@
 #include <sys/wait.h>
 #include "tst_test.h"
 #include "lapi/syscalls.h"
+#include "cma.h"
 
 static uintptr_t *data_ptr;
 
@@ -29,6 +30,8 @@ static void child_alloc(const char *data)
 
 	tst_res(TINFO, "child 0: memory allocated and initialized");
 
+	cma_allow_parent_ptracer();
+
 	/* wake and wait until child_invoke is done reading from our VM */
 	TST_CHECKPOINT_WAKE_AND_WAIT(0);
 }
@@ -64,6 +67,8 @@ static void setup(void)
 	/* Just a sanity check of the existence of syscall */
 	tst_syscall(__NR_process_vm_readv, getpid(), NULL, 0UL, NULL, 0UL, 0UL);
 
+	cma_check_ptrace_scope();
+
 	data_ptr = SAFE_MMAP(NULL, sizeof(uintptr_t), PROT_READ | PROT_WRITE,
 						 MAP_SHARED | MAP_ANONYMOUS, -1, 0);
 }
diff --git a/testcases/kernel/syscalls/cma/process_vm_readv03.c b/testcases/kernel/syscalls/cma/process_vm_readv03.c
index 95d35c422..831f79c89 100644
--- a/testcases/kernel/syscalls/cma/process_vm_readv03.c
+++ b/testcases/kernel/syscalls/cma/process_vm_readv03.c
@@ -20,6 +20,7 @@
 #include <sys/wait.h>
 #include "tst_test.h"
 #include "lapi/syscalls.h"
+#include "cma.h"
 
 #define MAX_IOVECS 1024
 
@@ -80,6 +81,8 @@ static void child_alloc(const int *sizes, int nr_iovecs)
 
 	tst_res(TINFO, "child_alloc: memory allocated and initialized");
 
+	cma_allow_parent_ptracer();
+
 	TST_CHECKPOINT_WAKE_AND_WAIT(0);
 }
 
@@ -139,6 +142,8 @@ static void setup(void)
 {
 	tst_syscall(__NR_process_vm_readv, getpid(), NULL, 0UL, NULL, 0UL, 0UL);
 
+	cma_check_ptrace_scope();
+
 	data_ptr = SAFE_MMAP(NULL, sizeof(void *) * MAX_IOVECS, PROT_READ | PROT_WRITE,
 			     MAP_SHARED | MAP_ANONYMOUS, -1, 0);
 }
diff --git a/testcases/kernel/syscalls/cma/process_vm_writev02.c b/testcases/kernel/syscalls/cma/process_vm_writev02.c
index 15bd66a44..78b98200f 100644
--- a/testcases/kernel/syscalls/cma/process_vm_writev02.c
+++ b/testcases/kernel/syscalls/cma/process_vm_writev02.c
@@ -16,6 +16,7 @@
 #include <sys/uio.h>
 #include "tst_test.h"
 #include "lapi/syscalls.h"
+#include "cma.h"
 
 static uintptr_t *data_ptr;
 static char *str_buffsize;
@@ -33,6 +34,8 @@ static void child_alloc_and_verify(int buffsize)
 	memset(foo, 'a', buffsize);
 	*data_ptr = (uintptr_t)foo;
 
+	cma_allow_parent_ptracer();
+
 	TST_CHECKPOINT_WAKE_AND_WAIT(0);
 
 	err = 0;
@@ -81,6 +84,8 @@ static void setup(void)
 	if (tst_parse_int(str_buffsize, &bufsize, 1, INT_MAX))
 		tst_brk(TBROK, "Invalid buffer size '%s'", str_buffsize);
 
+	cma_check_ptrace_scope();
+
 	data_ptr = SAFE_MMAP(NULL, sizeof(uintptr_t), PROT_READ | PROT_WRITE,
 			     MAP_SHARED | MAP_ANONYMOUS, -1, 0);
 }

-- 
2.51.0


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