[PATCH v10 0/4] liveupdate: bug fix for session name and new ioctl to read it

[PATCH v10 0/4] liveupdate: bug fix for session name and new ioctl to read it

[luca.boccassi]

From: Luca Boccassi <luca.boccassi@gmail.com>

A series of patches matured while implementing LUO support in userspace
in systemd.

- reject session names that are either empty strings or too long
- add new ioctl to retrieve session name from FD, so that userspace
  can query it without string parsing in procfs

Both changes come with a follow-up patch add test coverage via the
existing selftest.

v2: apply one fix from bot review about cleanup on error path:
    https://sashiko.dev/#/patchset/20260415184536.1155220-1-luca.boccassi%40gmail.com
    the other comments are invalid: luo is not a kmod, and the write hooks are not set up
v3: add test case to liveupdate selftest
v4: split test case in separate follow-up patch
v5: add r-b tag, merge series with LIVEUPDATE_SESSION_GET_NAME ioctl
    as they both change the same unit test source file, to avoid merge conflicts
    add '__u32 reserved' to the UAPI struct
v6: add more test cases as suggested
    more verbose commit message
    fix docstring
v7: apply suggestion from review bot to stub out setattr ops,
    like it was done in 22bdf3d6581a
v8: add new patches to reject session names that are empty or too long
v9: fixes following review comments on LUO_SESSION_MAGIC
v10: split out LUO_SESSION_MAGIC patch as it is undergoing more discussions,
     and the other two patches are independent aside from adding test cases
     to the same unit test source file

Luca Boccassi (4):
  liveupdate: reject LIVEUPDATE_IOCTL_CREATE_SESSION with invalid name
    length
  selftests/liveupdate: add test cases for
    LIVEUPDATE_IOCTL_CREATE_SESSION calls with invalid length
  liveupdate: add LIVEUPDATE_SESSION_GET_NAME ioctl
  selftests/liveupdate: add test cases for LIVEUPDATE_SESSION_GET_NAME

 include/uapi/linux/liveupdate.h               |  21 ++++
 kernel/liveupdate/luo_session.c               |  17 +++
 .../testing/selftests/liveupdate/liveupdate.c | 113 ++++++++++++++++++
 3 files changed, 151 insertions(+)

-- 
2.47.3

[PATCH v10 1/4] liveupdate: reject LIVEUPDATE_IOCTL_CREATE_SESSION with invalid name length

[luca.boccassi]

From: Luca Boccassi <luca.boccassi@gmail.com>

A session name must not be an empty string, and must not exceed the
maximum size define in the uapi header, including null termination.

Fixes: 0153094d03df ("liveupdate: luo_session: add sessions support")

Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 kernel/liveupdate/luo_session.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c
index 25ae704d7787..5e316a4c5d71 100644
--- a/kernel/liveupdate/luo_session.c
+++ b/kernel/liveupdate/luo_session.c
@@ -382,9 +382,13 @@ static int luo_session_getfile(struct luo_session *session, struct file **filep)
 
 int luo_session_create(const char *name, struct file **filep)
 {
+	size_t len = strnlen(name, LIVEUPDATE_SESSION_NAME_LENGTH);
 	struct luo_session *session;
 	int err;
 
+	if (len == 0 || len > LIVEUPDATE_SESSION_NAME_LENGTH - 1)
+		return -EINVAL;
+
 	session = luo_session_alloc(name);
 	if (IS_ERR(session))
 		return PTR_ERR(session);
-- 
2.47.3

[PATCH v10 2/4] selftests/liveupdate: add test cases for LIVEUPDATE_IOCTL_CREATE_SESSION calls with invalid length

[luca.boccassi]

From: Luca Boccassi <luca.boccassi@gmail.com>

Verify that LIVEUPDATE_IOCTL_CREATE_SESSION ioctl which provide a name
that is an empty string or too long are not allowed.

Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 .../testing/selftests/liveupdate/liveupdate.c | 42 +++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/tools/testing/selftests/liveupdate/liveupdate.c b/tools/testing/selftests/liveupdate/liveupdate.c
index c2878e3d5ef9..f0a8e600c154 100644
--- a/tools/testing/selftests/liveupdate/liveupdate.c
+++ b/tools/testing/selftests/liveupdate/liveupdate.c
@@ -345,4 +345,46 @@ TEST_F(liveupdate_device, preserve_unsupported_fd)
 	ASSERT_EQ(close(session_fd), 0);
 }
 
+/*
+ * Test Case: Create Session with No Null Termination
+ *
+ * Verifies that filling the entire 64-byte name field with non-null characters
+ * (no '\0' terminator) is rejected by the kernel with EINVAL.
+ */
+TEST_F(liveupdate_device, create_session_no_null_termination)
+{
+	struct liveupdate_ioctl_create_session args = {};
+
+	self->fd1 = open(LIVEUPDATE_DEV, O_RDWR);
+	if (self->fd1 < 0 && errno == ENOENT)
+		SKIP(return, "%s does not exist", LIVEUPDATE_DEV);
+	ASSERT_GE(self->fd1, 0);
+
+	/* Fill entire name field with 'X', no null terminator */
+	args.size = sizeof(args);
+	memset(args.name, 'X', sizeof(args.name));
+
+	EXPECT_LT(ioctl(self->fd1, LIVEUPDATE_IOCTL_CREATE_SESSION, &args), 0);
+	EXPECT_EQ(errno, EINVAL);
+}
+
+/*
+ * Test Case: Create Session with Empty Name
+ *
+ * Verifies that creating a session with an empty string name fails
+ * with EINVAL.
+ */
+TEST_F(liveupdate_device, create_session_empty_name)
+{
+	int session_fd;
+
+	self->fd1 = open(LIVEUPDATE_DEV, O_RDWR);
+	if (self->fd1 < 0 && errno == ENOENT)
+		SKIP(return, "%s does not exist", LIVEUPDATE_DEV);
+	ASSERT_GE(self->fd1, 0);
+
+	session_fd = create_session(self->fd1, "");
+	EXPECT_EQ(session_fd, -EINVAL);
+}
+
 TEST_HARNESS_MAIN
-- 
2.47.3

[PATCH v10 3/4] liveupdate: add LIVEUPDATE_SESSION_GET_NAME ioctl

[luca.boccassi]

From: Luca Boccassi <luca.boccassi@gmail.com>

Userspace when requesting a session via the ioctl specifies a name and
gets a FD, but then there is no ioctl to go back the other way and get
the name given a LUO session FD. This is problematic especially when
there is a userspace orchestrator that wants to check what FDs it is
handling for clients without having to do manual string scraping of
procfs, or without procfs at all.

Add a ioctl to simply get the name from an FD.

Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 include/uapi/linux/liveupdate.h | 21 +++++++++++++++++++++
 kernel/liveupdate/luo_session.c | 13 +++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/include/uapi/linux/liveupdate.h b/include/uapi/linux/liveupdate.h
index 30bc66ee9436..3a9ff53b02e0 100644
--- a/include/uapi/linux/liveupdate.h
+++ b/include/uapi/linux/liveupdate.h
@@ -59,6 +59,7 @@ enum {
 	LIVEUPDATE_CMD_SESSION_PRESERVE_FD = LIVEUPDATE_CMD_SESSION_BASE,
 	LIVEUPDATE_CMD_SESSION_RETRIEVE_FD = 0x41,
 	LIVEUPDATE_CMD_SESSION_FINISH = 0x42,
+	LIVEUPDATE_CMD_SESSION_GET_NAME = 0x43,
 };
 
 /**
@@ -213,4 +214,24 @@ struct liveupdate_session_finish {
 #define LIVEUPDATE_SESSION_FINISH					\
 	_IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_SESSION_FINISH)
 
+/**
+ * struct liveupdate_session_get_name - ioctl(LIVEUPDATE_SESSION_GET_NAME)
+ * @size:  Input; sizeof(struct liveupdate_session_get_name)
+ * @reserved: Input; Must be zero. Reserved for future use.
+ * @name:  Output; A null-terminated string with the full session name.
+ *
+ * Retrieves the full name of the session associated with this file descriptor.
+ * This is useful because the kernel may truncate the name shown in /proc.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+struct liveupdate_session_get_name {
+	__u32		size;
+	__u32		reserved;
+	__u8		name[LIVEUPDATE_SESSION_NAME_LENGTH];
+};
+
+#define LIVEUPDATE_SESSION_GET_NAME					\
+	_IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_SESSION_GET_NAME)
+
 #endif /* _UAPI_LIVEUPDATE_H */
diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c
index 5e316a4c5d71..0bcf2def074e 100644
--- a/kernel/liveupdate/luo_session.c
+++ b/kernel/liveupdate/luo_session.c
@@ -289,10 +289,21 @@ static int luo_session_finish(struct luo_session *session,
 	return luo_ucmd_respond(ucmd, sizeof(*argp));
 }
 
+static int luo_session_get_name(struct luo_session *session,
+				struct luo_ucmd *ucmd)
+{
+	struct liveupdate_session_get_name *argp = ucmd->cmd;
+
+	strscpy((char *)argp->name, session->name, sizeof(argp->name));
+
+	return luo_ucmd_respond(ucmd, sizeof(*argp));
+}
+
 union ucmd_buffer {
 	struct liveupdate_session_finish finish;
 	struct liveupdate_session_preserve_fd preserve;
 	struct liveupdate_session_retrieve_fd retrieve;
+	struct liveupdate_session_get_name get_name;
 };
 
 struct luo_ioctl_op {
@@ -319,6 +330,8 @@ static const struct luo_ioctl_op luo_session_ioctl_ops[] = {
 		 struct liveupdate_session_preserve_fd, token),
 	IOCTL_OP(LIVEUPDATE_SESSION_RETRIEVE_FD, luo_session_retrieve_fd,
 		 struct liveupdate_session_retrieve_fd, token),
+	IOCTL_OP(LIVEUPDATE_SESSION_GET_NAME, luo_session_get_name,
+		 struct liveupdate_session_get_name, name),
 };
 
 static long luo_session_ioctl(struct file *filep, unsigned int cmd,
-- 
2.47.3

[PATCH v10 4/4] selftests/liveupdate: add test cases for LIVEUPDATE_SESSION_GET_NAME

[luca.boccassi]

From: Luca Boccassi <luca.boccassi@gmail.com>

Verify that the new LIVEUPDATE_SESSION_GET_NAME ioctl works
as expected via new test cases in the existing liveupdate selftest.

Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 .../testing/selftests/liveupdate/liveupdate.c | 71 +++++++++++++++++++
 1 file changed, 71 insertions(+)

diff --git a/tools/testing/selftests/liveupdate/liveupdate.c b/tools/testing/selftests/liveupdate/liveupdate.c
index f0a8e600c154..eda832125809 100644
--- a/tools/testing/selftests/liveupdate/liveupdate.c
+++ b/tools/testing/selftests/liveupdate/liveupdate.c
@@ -102,6 +102,22 @@ static int create_session(int lu_fd, const char *name)
 	return args.fd;
 }
 
+/* Helper function to get a session name via ioctl. */
+static int get_session_name(int session_fd, char *name, size_t name_len)
+{
+	struct liveupdate_session_get_name args = {};
+
+	args.size = sizeof(args);
+
+	if (ioctl(session_fd, LIVEUPDATE_SESSION_GET_NAME, &args))
+		return -errno;
+
+	strncpy(name, (char *)args.name, name_len - 1);
+	name[name_len - 1] = '\0';
+
+	return 0;
+}
+
 /*
  * Test Case: Create Duplicate Session
  *
@@ -387,4 +403,59 @@ TEST_F(liveupdate_device, create_session_empty_name)
 	EXPECT_EQ(session_fd, -EINVAL);
 }
 
+/*
+ * Test Case: Get Session Name
+ *
+ * Verifies that the full session name can be retrieved from a session file
+ * descriptor via ioctl.
+ */
+TEST_F(liveupdate_device, get_session_name)
+{
+	char name_buf[LIVEUPDATE_SESSION_NAME_LENGTH] = {};
+	const char *session_name = "get-name-test-session";
+	int session_fd;
+
+	self->fd1 = open(LIVEUPDATE_DEV, O_RDWR);
+	if (self->fd1 < 0 && errno == ENOENT)
+		SKIP(return, "%s does not exist", LIVEUPDATE_DEV);
+	ASSERT_GE(self->fd1, 0);
+
+	session_fd = create_session(self->fd1, session_name);
+	ASSERT_GE(session_fd, 0);
+
+	ASSERT_EQ(get_session_name(session_fd, name_buf, sizeof(name_buf)), 0);
+	ASSERT_STREQ(name_buf, session_name);
+
+	ASSERT_EQ(close(session_fd), 0);
+}
+
+/*
+ * Test Case: Get Session Name at Maximum Length
+ *
+ * Verifies that a session name using the full LIVEUPDATE_SESSION_NAME_LENGTH
+ * (minus the null terminator) can be correctly retrieved.
+ */
+TEST_F(liveupdate_device, get_session_name_max_length)
+{
+	char name_buf[LIVEUPDATE_SESSION_NAME_LENGTH] = {};
+	char long_name[LIVEUPDATE_SESSION_NAME_LENGTH];
+	int session_fd;
+
+	memset(long_name, 'A', sizeof(long_name) - 1);
+	long_name[sizeof(long_name) - 1] = '\0';
+
+	self->fd1 = open(LIVEUPDATE_DEV, O_RDWR);
+	if (self->fd1 < 0 && errno == ENOENT)
+		SKIP(return, "%s does not exist", LIVEUPDATE_DEV);
+	ASSERT_GE(self->fd1, 0);
+
+	session_fd = create_session(self->fd1, long_name);
+	ASSERT_GE(session_fd, 0);
+
+	ASSERT_EQ(get_session_name(session_fd, name_buf, sizeof(name_buf)), 0);
+	ASSERT_STREQ(name_buf, long_name);
+
+	ASSERT_EQ(close(session_fd), 0);
+}
+
 TEST_HARNESS_MAIN
-- 
2.47.3

Re: [PATCH v10 1/4] liveupdate: reject LIVEUPDATE_IOCTL_CREATE_SESSION with invalid name length

[Pratyush Yadav]

On Fri, Apr 24 2026, luca.boccassi@gmail.com wrote:

> From: Luca Boccassi <luca.boccassi@gmail.com>
>
> A session name must not be an empty string, and must not exceed the
> maximum size define in the uapi header, including null termination.
>
> Fixes: 0153094d03df ("liveupdate: luo_session: add sessions support")
>
> Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
> Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Reviewed-by: Pratyush Yadav <pratyush@kernel.org>

Cc: stable?

[...]

-- 
Regards,
Pratyush Yadav

Re: [PATCH v10 1/4] liveupdate: reject LIVEUPDATE_IOCTL_CREATE_SESSION with invalid name length

[Luca Boccassi]

On Wed, 29 Apr 2026 at 15:24, Pratyush Yadav <pratyush@kernel.org> wrote:
>
> On Fri, Apr 24 2026, luca.boccassi@gmail.com wrote:
>
> > From: Luca Boccassi <luca.boccassi@gmail.com>
> >
> > A session name must not be an empty string, and must not exceed the
> > maximum size define in the uapi header, including null termination.
> >
> > Fixes: 0153094d03df ("liveupdate: luo_session: add sessions support")
> >
> > Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
> > Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> > Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
>
> Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
>
> Cc: stable?

Yeah that would be good, can it be added when merging please?

Re: [PATCH v10 2/4] selftests/liveupdate: add test cases for LIVEUPDATE_IOCTL_CREATE_SESSION calls with invalid length

[Pratyush Yadav]

On Fri, Apr 24 2026, luca.boccassi@gmail.com wrote:

> From: Luca Boccassi <luca.boccassi@gmail.com>
>
> Verify that LIVEUPDATE_IOCTL_CREATE_SESSION ioctl which provide a name
> that is an empty string or too long are not allowed.
>
> Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
> Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Reviewed-by: Pratyush Yadav <pratyush@kernel.org>

[...]

-- 
Regards,
Pratyush Yadav

Re: [PATCH v10 3/4] liveupdate: add LIVEUPDATE_SESSION_GET_NAME ioctl

[Pratyush Yadav]

On Fri, Apr 24 2026, luca.boccassi@gmail.com wrote:

> From: Luca Boccassi <luca.boccassi@gmail.com>
>
> Userspace when requesting a session via the ioctl specifies a name and
> gets a FD, but then there is no ioctl to go back the other way and get
> the name given a LUO session FD. This is problematic especially when
> there is a userspace orchestrator that wants to check what FDs it is
> handling for clients without having to do manual string scraping of
> procfs, or without procfs at all.
>
> Add a ioctl to simply get the name from an FD.
>
> Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
> Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
>  include/uapi/linux/liveupdate.h | 21 +++++++++++++++++++++
>  kernel/liveupdate/luo_session.c | 13 +++++++++++++
>  2 files changed, 34 insertions(+)
>
> diff --git a/include/uapi/linux/liveupdate.h b/include/uapi/linux/liveupdate.h
> index 30bc66ee9436..3a9ff53b02e0 100644
> --- a/include/uapi/linux/liveupdate.h
> +++ b/include/uapi/linux/liveupdate.h
> @@ -59,6 +59,7 @@ enum {
>  	LIVEUPDATE_CMD_SESSION_PRESERVE_FD = LIVEUPDATE_CMD_SESSION_BASE,
>  	LIVEUPDATE_CMD_SESSION_RETRIEVE_FD = 0x41,
>  	LIVEUPDATE_CMD_SESSION_FINISH = 0x42,
> +	LIVEUPDATE_CMD_SESSION_GET_NAME = 0x43,
>  };
>  
>  /**
> @@ -213,4 +214,24 @@ struct liveupdate_session_finish {
>  #define LIVEUPDATE_SESSION_FINISH					\
>  	_IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_SESSION_FINISH)
>  
> +/**
> + * struct liveupdate_session_get_name - ioctl(LIVEUPDATE_SESSION_GET_NAME)
> + * @size:  Input; sizeof(struct liveupdate_session_get_name)
> + * @reserved: Input; Must be zero. Reserved for future use.

You need to enforce this in luo_session_get_name(). Otherwise some
userspace might try to get clever and stash some data here. Then if we
ever put something else here it will break that userspace.

With this fixed,

Reviewed-by: Pratyush Yadav <pratyush@kernel.org>

> + * @name:  Output; A null-terminated string with the full session name.
> + *
> + * Retrieves the full name of the session associated with this file descriptor.
> + * This is useful because the kernel may truncate the name shown in /proc.
> + *
> + * Return: 0 on success, negative error code on failure.
> + */
> +struct liveupdate_session_get_name {
> +	__u32		size;
> +	__u32		reserved;
> +	__u8		name[LIVEUPDATE_SESSION_NAME_LENGTH];
> +};
> +
> +#define LIVEUPDATE_SESSION_GET_NAME					\
> +	_IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_SESSION_GET_NAME)
> +
>  #endif /* _UAPI_LIVEUPDATE_H */
> diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c
> index 5e316a4c5d71..0bcf2def074e 100644
> --- a/kernel/liveupdate/luo_session.c
> +++ b/kernel/liveupdate/luo_session.c
> @@ -289,10 +289,21 @@ static int luo_session_finish(struct luo_session *session,
>  	return luo_ucmd_respond(ucmd, sizeof(*argp));
>  }
>  
> +static int luo_session_get_name(struct luo_session *session,
> +				struct luo_ucmd *ucmd)
> +{
> +	struct liveupdate_session_get_name *argp = ucmd->cmd;
> +
> +	strscpy((char *)argp->name, session->name, sizeof(argp->name));
> +
> +	return luo_ucmd_respond(ucmd, sizeof(*argp));
> +}
> +
>  union ucmd_buffer {
>  	struct liveupdate_session_finish finish;
>  	struct liveupdate_session_preserve_fd preserve;
>  	struct liveupdate_session_retrieve_fd retrieve;
> +	struct liveupdate_session_get_name get_name;
>  };
>  
>  struct luo_ioctl_op {
> @@ -319,6 +330,8 @@ static const struct luo_ioctl_op luo_session_ioctl_ops[] = {
>  		 struct liveupdate_session_preserve_fd, token),
>  	IOCTL_OP(LIVEUPDATE_SESSION_RETRIEVE_FD, luo_session_retrieve_fd,
>  		 struct liveupdate_session_retrieve_fd, token),
> +	IOCTL_OP(LIVEUPDATE_SESSION_GET_NAME, luo_session_get_name,
> +		 struct liveupdate_session_get_name, name),
>  };
>  
>  static long luo_session_ioctl(struct file *filep, unsigned int cmd,

-- 
Regards,
Pratyush Yadav

Re: [PATCH v10 4/4] selftests/liveupdate: add test cases for LIVEUPDATE_SESSION_GET_NAME

[Pratyush Yadav]

On Fri, Apr 24 2026, luca.boccassi@gmail.com wrote:

> From: Luca Boccassi <luca.boccassi@gmail.com>
>
> Verify that the new LIVEUPDATE_SESSION_GET_NAME ioctl works
> as expected via new test cases in the existing liveupdate selftest.
>
> Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
> Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Reviewed-by: Pratyush Yadav <pratyush@kernel.org>

[...]

-- 
Regards,
Pratyush Yadav