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Message-ID: <4ad606c2-c7d1-4463-a2f1-4fd0c63c6e9b@schaufler-ca.com>
Date: Thu, 19 Dec 2024 13:34:14 -0800
From: Casey Schaufler <casey@...aufler-ca.com>
To: Hamza Mahfooz <hamzamahfooz@...ux.microsoft.com>,
linux-security-module@...r.kernel.org, io-uring@...r.kernel.org
Cc: Paul Moore <paul@...l-moore.com>, Jens Axboe <axboe@...nel.dk>,
James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>,
Pavel Begunkov <asml.silence@...il.com>,
Stephen Smalley <stephen.smalley.work@...il.com>,
Ondrej Mosnacek <omosnace@...hat.com>, Thiébaud Weksteen
<tweek@...gle.com>, Masahiro Yamada <masahiroy@...nel.org>,
Bram Bonné <brambonne@...gle.com>,
linux-kernel@...r.kernel.org, selinux@...r.kernel.org,
Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH] lsm,io_uring: add LSM hooks for io_uring_setup()
On 12/19/2024 12:41 PM, Hamza Mahfooz wrote:
> It is desirable to allow LSM to configure accessibility to io_uring.
Why is it desirable to allow LSM to configure accessibility to io_uring?
> So,
> add an LSM for io_uring_allowed() to guard access to io_uring.
>
> Cc: Paul Moore <paul@...l-moore.com>
> Cc: Jens Axboe <axboe@...nel.dk>
> Signed-off-by: Hamza Mahfooz <hamzamahfooz@...ux.microsoft.com>
> ---
> include/linux/lsm_hook_defs.h | 1 +
> include/linux/security.h | 5 +++++
> io_uring/io_uring.c | 21 ++++++++++++++-------
> security/security.c | 12 ++++++++++++
> security/selinux/hooks.c | 14 ++++++++++++++
> security/selinux/include/classmap.h | 2 +-
> 6 files changed, 47 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index eb2937599cb0..ee45229418dd 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -456,6 +456,7 @@ LSM_HOOK(int, 0, perf_event_write, struct perf_event *event)
> LSM_HOOK(int, 0, uring_override_creds, const struct cred *new)
> LSM_HOOK(int, 0, uring_sqpoll, void)
> LSM_HOOK(int, 0, uring_cmd, struct io_uring_cmd *ioucmd)
> +LSM_HOOK(int, 0, uring_allowed, void)
> #endif /* CONFIG_IO_URING */
>
> LSM_HOOK(void, LSM_RET_VOID, initramfs_populated, void)
> diff --git a/include/linux/security.h b/include/linux/security.h
> index cbdba435b798..0a5e897289e8 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -2351,6 +2351,7 @@ static inline int security_perf_event_write(struct perf_event *event)
> extern int security_uring_override_creds(const struct cred *new);
> extern int security_uring_sqpoll(void);
> extern int security_uring_cmd(struct io_uring_cmd *ioucmd);
> +extern int security_uring_allowed(void);
> #else
> static inline int security_uring_override_creds(const struct cred *new)
> {
> @@ -2364,6 +2365,10 @@ static inline int security_uring_cmd(struct io_uring_cmd *ioucmd)
> {
> return 0;
> }
> +extern int security_uring_allowed(void)
> +{
> + return 0;
> +}
> #endif /* CONFIG_SECURITY */
> #endif /* CONFIG_IO_URING */
>
> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> index 06ff41484e29..0922bb0724c0 100644
> --- a/io_uring/io_uring.c
> +++ b/io_uring/io_uring.c
> @@ -3806,29 +3806,36 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params)
> return io_uring_create(entries, &p, params);
> }
>
> -static inline bool io_uring_allowed(void)
> +static inline int io_uring_allowed(void)
> {
> int disabled = READ_ONCE(sysctl_io_uring_disabled);
> kgid_t io_uring_group;
>
> if (disabled == 2)
> - return false;
> + return -EPERM;
>
> if (disabled == 0 || capable(CAP_SYS_ADMIN))
> - return true;
> + goto allowed_lsm;
>
> io_uring_group = make_kgid(&init_user_ns, sysctl_io_uring_group);
> if (!gid_valid(io_uring_group))
> - return false;
> + return -EPERM;
> +
> + if (!in_group_p(io_uring_group))
> + return -EPERM;
>
> - return in_group_p(io_uring_group);
> +allowed_lsm:
> + return security_uring_allowed();
> }
>
> SYSCALL_DEFINE2(io_uring_setup, u32, entries,
> struct io_uring_params __user *, params)
> {
> - if (!io_uring_allowed())
> - return -EPERM;
> + int ret;
> +
> + ret = io_uring_allowed();
> + if (ret)
> + return ret;
>
> return io_uring_setup(entries, params);
> }
> diff --git a/security/security.c b/security/security.c
> index 09664e09fec9..e4d532e4ead4 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -5996,6 +5996,18 @@ int security_uring_cmd(struct io_uring_cmd *ioucmd)
> {
> return call_int_hook(uring_cmd, ioucmd);
> }
> +
> +/**
> + * security_uring_allowed() - Check if io_uring_setup() is allowed
> + *
> + * Check whether the current task is allowed to call io_uring_setup().
> + *
> + * Return: Returns 0 if permission is granted.
> + */
> +int security_uring_allowed(void)
> +{
> + return call_int_hook(uring_allowed);
> +}
> #endif /* CONFIG_IO_URING */
>
> /**
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 366c87a40bd1..b4e298c51c16 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -7117,6 +7117,19 @@ static int selinux_uring_cmd(struct io_uring_cmd *ioucmd)
> return avc_has_perm(current_sid(), isec->sid,
> SECCLASS_IO_URING, IO_URING__CMD, &ad);
> }
> +
> +/**
> + * selinux_uring_allowed - check if io_uring_setup() can be called
> + *
> + * Check to see if the current task is allowed to call io_uring_setup().
> + */
> +static int selinux_uring_allowed(void)
> +{
> + u32 sid = current_sid();
> +
> + return avc_has_perm(sid, sid, SECCLASS_IO_URING, IO_URING__ALLOWED,
> + NULL);
> +}
> #endif /* CONFIG_IO_URING */
>
> static const struct lsm_id selinux_lsmid = {
> @@ -7370,6 +7383,7 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
> LSM_HOOK_INIT(uring_override_creds, selinux_uring_override_creds),
> LSM_HOOK_INIT(uring_sqpoll, selinux_uring_sqpoll),
> LSM_HOOK_INIT(uring_cmd, selinux_uring_cmd),
> + LSM_HOOK_INIT(uring_allowed, selinux_uring_allowed),
> #endif
>
> /*
> diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
> index 2bc20135324a..5ae222f7e543 100644
> --- a/security/selinux/include/classmap.h
> +++ b/security/selinux/include/classmap.h
> @@ -177,7 +177,7 @@ const struct security_class_mapping secclass_map[] = {
> { "perf_event",
> { "open", "cpu", "kernel", "tracepoint", "read", "write", NULL } },
> { "anon_inode", { COMMON_FILE_PERMS, NULL } },
> - { "io_uring", { "override_creds", "sqpoll", "cmd", NULL } },
> + { "io_uring", { "override_creds", "sqpoll", "cmd", "allowed", NULL } },
> { "user_namespace", { "create", NULL } },
> { NULL }
> };
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