* [LTP] [PATCH v3 2/2] syscalls/cma: Handle Yama ptrace_scope in tests
2026-10-20 10:37 [LTP] [PATCH v3 0/2] Fix cma testing suite permissions Andrea Cervesato
2026-10-20 10:37 ` [LTP] [PATCH v3 1/2] lapi/capability.h: Add CAP_SYS_PTRACE fallback Andrea Cervesato
@ 2026-10-20 10:37 ` Andrea Cervesato
1 sibling, 0 replies; 4+ messages in thread
From: Andrea Cervesato @ 2026-10-20 10:37 UTC (permalink / raw)
To: Linux Test Project
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
--
Mailing list info: https://lists.linux.it/listinfo/ltp
^ permalink raw reply related [flat|nested] 4+ messages in thread