This patch adds basic auditing to io_uring operations, regardless of their context. This is accomplished by allocating audit_context structures for the io-wq worker and io_uring SQPOLL kernel threads as well as explicitly auditing the io_uring operations in io_issue_sqe(). Individual io_uring operations can bypass auditing through the "audit_skip" field in the struct io_op_def definition for the operation; although great care must be taken so that security relevant io_uring operations do not bypass auditing; please contact the audit mailing list (see the MAINTAINERS file) with any questions. The io_uring operations are audited using a new AUDIT_URINGOP record, an example is shown below: type=UNKNOWN[1336] msg=audit(1630523381.288:260): uring_op=19 success=yes exit=0 items=0 ppid=853 pid=1204 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 key=(null) AUID="root" UID="root" GID="root" EUID="root" SUID="root" FSUID="root" EGID="root" SGID="root" FSGID="root" Thanks to Richard Guy Briggs for review and feedback. Signed-off-by: Paul Moore <paul(a)paul-moore.com&gt; --- v4: - removed some work-in-progress comments - removed the auid logging in audit_log_uring() v3: - removed work-in-progress warning from the description v2: - added dummy funcs for audit_uring_{entry,exit}() - replaced opcode checks in io_issue_sqe() with audit_skip checks - moved fastpath checks into audit_uring_{entry,exit}() - audit_log_uring() uses GFP_ATOMIC - don't record the arch in __audit_uring_entry() v1: - initial draft --- fs/io-wq.c | 4 + fs/io_uring.c | 55 +++++++++++++-- include/linux/audit.h | 26 +++++++ include/uapi/linux/audit.h | 1 kernel/audit.h | 2 + kernel/auditsc.c | 166 ++++++++++++++++++++++++++++++++++++++++++++ 6 files changed, 248 insertions(+), 6 deletions(-) diff --git a/fs/io-wq.c b/fs/io-wq.c index 6c55362c1f99..dac5c5961c9d 100644 --- a/fs/io-wq.c +++ b/fs/io-wq.c @@ -14,6 +14,7 @@ #include <linux/rculist_nulls.h> #include <linux/cpu.h> #include <linux/tracehook.h> +#include <linux/audit.h> #include "io-wq.h" @@ -562,6 +563,8 @@ static int io_wqe_worker(void *data) snprintf(buf, sizeof(buf), "iou-wrk-%d", wq->task->pid); set_task_comm(current, buf); + audit_alloc_kernel(current); + while (!test_bit(IO_WQ_BIT_EXIT, &wq->state)) { long ret; @@ -601,6 +604,7 @@ static int io_wqe_worker(void *data) io_worker_handle_work(worker); } + audit_free(current); io_worker_exit(worker); return 0; } diff --git a/fs/io_uring.c b/fs/io_uring.c index 16fb7436043c..388754b24785 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -79,6 +79,7 @@ #include <linux/pagemap.h> #include <linux/io_uring.h> #include <linux/tracehook.h> +#include <linux/audit.h> #define CREATE_TRACE_POINTS #include <trace/events/io_uring.h> @@ -917,6 +918,8 @@ struct io_op_def { unsigned needs_async_setup : 1; /* should block plug */ unsigned plug : 1; + /* skip auditing */ + unsigned audit_skip : 1; /* size of async data needed, if any */ unsigned short async_size; }; @@ -930,6 +933,7 @@ static const struct io_op_def io_op_defs[] = { .buffer_select = 1, .needs_async_setup = 1, .plug = 1, + .audit_skip = 1, .async_size = sizeof(struct io_async_rw), }, [IORING_OP_WRITEV] = { @@ -939,16 +943,19 @@ static const struct io_op_def io_op_defs[] = { .pollout = 1, .needs_async_setup = 1, .plug = 1, + .audit_skip = 1, .async_size = sizeof(struct io_async_rw), }, [IORING_OP_FSYNC] = { .needs_file = 1, + .audit_skip = 1, }, [IORING_OP_READ_FIXED] = { .needs_file = 1, .unbound_nonreg_file = 1, .pollin = 1, .plug = 1, + .audit_skip = 1, .async_size = sizeof(struct io_async_rw), }, [IORING_OP_WRITE_FIXED] = { @@ -957,15 +964,20 @@ static const struct io_op_def io_op_defs[] = { .unbound_nonreg_file = 1, .pollout = 1, .plug = 1, + .audit_skip = 1, .async_size = sizeof(struct io_async_rw), }, [IORING_OP_POLL_ADD] = { .needs_file = 1, .unbound_nonreg_file = 1, + .audit_skip = 1, + }, + [IORING_OP_POLL_REMOVE] = { + .audit_skip = 1, }, - [IORING_OP_POLL_REMOVE] = {}, [IORING_OP_SYNC_FILE_RANGE] = { .needs_file = 1, + .audit_skip = 1, }, [IORING_OP_SENDMSG] = { .needs_file = 1, @@ -983,18 +995,23 @@ static const struct io_op_def io_op_defs[] = { .async_size = sizeof(struct io_async_msghdr), }, [IORING_OP_TIMEOUT] = { + .audit_skip = 1, .async_size = sizeof(struct io_timeout_data), }, [IORING_OP_TIMEOUT_REMOVE] = { /* used by timeout updates' prep() */ + .audit_skip = 1, }, [IORING_OP_ACCEPT] = { .needs_file = 1, .unbound_nonreg_file = 1, .pollin = 1, }, - [IORING_OP_ASYNC_CANCEL] = {}, + [IORING_OP_ASYNC_CANCEL] = { + .audit_skip = 1, + }, [IORING_OP_LINK_TIMEOUT] = { + .audit_skip = 1, .async_size = sizeof(struct io_timeout_data), }, [IORING_OP_CONNECT] = { @@ -1009,14 +1026,19 @@ static const struct io_op_def io_op_defs[] = { }, [IORING_OP_OPENAT] = {}, [IORING_OP_CLOSE] = {}, - [IORING_OP_FILES_UPDATE] = {}, - [IORING_OP_STATX] = {}, + [IORING_OP_FILES_UPDATE] = { + .audit_skip = 1, + }, + [IORING_OP_STATX] = { + .audit_skip = 1, + }, [IORING_OP_READ] = { .needs_file = 1, .unbound_nonreg_file = 1, .pollin = 1, .buffer_select = 1, .plug = 1, + .audit_skip = 1, .async_size = sizeof(struct io_async_rw), }, [IORING_OP_WRITE] = { @@ -1025,39 +1047,50 @@ static const struct io_op_def io_op_defs[] = { .unbound_nonreg_file = 1, .pollout = 1, .plug = 1, + .audit_skip = 1, .async_size = sizeof(struct io_async_rw), }, [IORING_OP_FADVISE] = { .needs_file = 1, + .audit_skip = 1, }, [IORING_OP_MADVISE] = {}, [IORING_OP_SEND] = { .needs_file = 1, .unbound_nonreg_file = 1, .pollout = 1, + .audit_skip = 1, }, [IORING_OP_RECV] = { .needs_file = 1, .unbound_nonreg_file = 1, .pollin = 1, .buffer_select = 1, + .audit_skip = 1, }, [IORING_OP_OPENAT2] = { }, [IORING_OP_EPOLL_CTL] = { .unbound_nonreg_file = 1, + .audit_skip = 1, }, [IORING_OP_SPLICE] = { .needs_file = 1, .hash_reg_file = 1, .unbound_nonreg_file = 1, + .audit_skip = 1, + }, + [IORING_OP_PROVIDE_BUFFERS] = { + .audit_skip = 1, + }, + [IORING_OP_REMOVE_BUFFERS] = { + .audit_skip = 1, }, - [IORING_OP_PROVIDE_BUFFERS] = {}, - [IORING_OP_REMOVE_BUFFERS] = {}, [IORING_OP_TEE] = { .needs_file = 1, .hash_reg_file = 1, .unbound_nonreg_file = 1, + .audit_skip = 1, }, [IORING_OP_SHUTDOWN] = { .needs_file = 1, @@ -6591,6 +6624,9 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags) if ((req->flags & REQ_F_CREDS) && req->creds != current_cred()) creds = override_creds(req->creds); + if (!io_op_defs[req->opcode].audit_skip) + audit_uring_entry(req->opcode); + switch (req->opcode) { case IORING_OP_NOP: ret = io_nop(req, issue_flags); @@ -6706,6 +6742,9 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags) break; } + if (!io_op_defs[req->opcode].audit_skip) + audit_uring_exit(!ret, ret); + if (creds) revert_creds(creds); if (ret) @@ -7360,6 +7399,8 @@ static int io_sq_thread(void *data) set_cpus_allowed_ptr(current, cpu_online_mask); current->flags |= PF_NO_SETAFFINITY; + audit_alloc_kernel(current); + mutex_lock(&sqd->lock); while (1) { bool cap_entries, sqt_spin = false; @@ -7425,6 +7466,8 @@ static int io_sq_thread(void *data) io_run_task_work(); mutex_unlock(&sqd->lock); + audit_free(current); + complete(&sqd->exited); do_exit(0); } diff --git a/include/linux/audit.h b/include/linux/audit.h index 82b7c1116a85..d656a06dd909 100644 --- a/include/linux/audit.h +++ b/include/linux/audit.h @@ -286,7 +286,10 @@ static inline int audit_signal_info(int sig, struct task_struct *t) /* These are defined in auditsc.c */ /* Public API */ extern int audit_alloc(struct task_struct *task); +extern int audit_alloc_kernel(struct task_struct *task); extern void __audit_free(struct task_struct *task); +extern void __audit_uring_entry(u8 op); +extern void __audit_uring_exit(int success, long code); extern void __audit_syscall_entry(int major, unsigned long a0, unsigned long a1, unsigned long a2, unsigned long a3); extern void __audit_syscall_exit(int ret_success, long ret_value); @@ -323,6 +326,21 @@ static inline void audit_free(struct task_struct *task) if (unlikely(task->audit_context)) __audit_free(task); } +static inline void audit_uring_entry(u8 op) +{ + /* + * We intentionally check audit_context() before audit_enabled as most + * Linux systems (as of ~2021) rely on systemd which forces audit to + * be enabled regardless of the user's audit configuration. + */ + if (unlikely(audit_context() && audit_enabled)) + __audit_uring_entry(op); +} +static inline void audit_uring_exit(int success, long code) +{ + if (unlikely(!audit_dummy_context())) + __audit_uring_exit(success, code); +} static inline void audit_syscall_entry(int major, unsigned long a0, unsigned long a1, unsigned long a2, unsigned long a3) @@ -554,8 +572,16 @@ static inline int audit_alloc(struct task_struct *task) { return 0; } +static inline int audit_alloc_kernel(struct task_struct *task) +{ + return 0; +} static inline void audit_free(struct task_struct *task) { } +static inline void audit_uring_entry(u8 op) +{ } +static inline void audit_uring_exit(int success, long code) +{ } static inline void audit_syscall_entry(int major, unsigned long a0, unsigned long a1, unsigned long a2, unsigned long a3) diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h index daa481729e9b..a1997697c8b1 100644 --- a/include/uapi/linux/audit.h +++ b/include/uapi/linux/audit.h @@ -118,6 +118,7 @@ #define AUDIT_TIME_ADJNTPVAL 1333 /* NTP value adjustment */ #define AUDIT_BPF 1334 /* BPF subsystem */ #define AUDIT_EVENT_LISTENER 1335 /* Task joined multicast read socket */ +#define AUDIT_URINGOP 1336 /* io_uring operation */ #define AUDIT_AVC 1400 /* SE Linux avc denial or grant */ #define AUDIT_SELINUX_ERR 1401 /* Internal SE Linux Errors */ diff --git a/kernel/audit.h b/kernel/audit.h index 13abc48de0bd..d1161e3b83e2 100644 --- a/kernel/audit.h +++ b/kernel/audit.h @@ -103,10 +103,12 @@ struct audit_context { enum { AUDIT_CTX_UNUSED, /* audit_context is currently unused */ AUDIT_CTX_SYSCALL, /* in use by syscall */ + AUDIT_CTX_URING, /* in use by io_uring */ } context; enum audit_state state, current_state; unsigned int serial; /* serial number for record */ int major; /* syscall number */ + int uring_op; /* uring operation */ struct timespec64 ctime; /* time of syscall entry */ unsigned long argv[4]; /* syscall arguments */ long return_code;/* syscall return code */ diff --git a/kernel/auditsc.c b/kernel/auditsc.c index f3d309b05c2d..6dda448fb826 100644 --- a/kernel/auditsc.c +++ b/kernel/auditsc.c @@ -959,6 +959,7 @@ static void audit_reset_context(struct audit_context *ctx) ctx->current_state = ctx->state; ctx->serial = 0; ctx->major = 0; + ctx->uring_op = 0; ctx->ctime = (struct timespec64){ .tv_sec = 0, .tv_nsec = 0 }; memset(ctx->argv, 0, sizeof(ctx->argv)); ctx->return_code = 0; @@ -1044,6 +1045,31 @@ int audit_alloc(struct task_struct *tsk) return 0; } +/** + * audit_alloc_kernel - allocate an audit_context for a kernel task + * @tsk: the kernel task + * + * Similar to the audit_alloc() function, but intended for kernel private + * threads. Returns zero on success, negative values on failure. + */ +int audit_alloc_kernel(struct task_struct *tsk) +{ + /* + * At the moment we are just going to call into audit_alloc() to + * simplify the code, but there two things to keep in mind with this + * approach: + * + * 1. Filtering internal kernel tasks is a bit laughable in almost all + * cases, but there is at least one case where there is a benefit: + * the '-a task,never' case allows the admin to effectively disable + * task auditing at runtime. + * + * 2. The {set,clear}_task_syscall_work() ops likely have zero effect + * on these internal kernel tasks, but they probably don't hurt either. + */ + return audit_alloc(tsk); +} + static inline void audit_free_context(struct audit_context *context) { /* resetting is extra work, but it is likely just noise */ @@ -1546,6 +1572,44 @@ static void audit_log_proctitle(void) audit_log_end(ab); } +/** + * audit_log_uring - generate a AUDIT_URINGOP record + * @ctx: the audit context + */ +static void audit_log_uring(struct audit_context *ctx) +{ + struct audit_buffer *ab; + const struct cred *cred; + + ab = audit_log_start(ctx, GFP_ATOMIC, AUDIT_URINGOP); + if (!ab) + return; + cred = current_cred(); + audit_log_format(ab, "uring_op=%d", ctx->uring_op); + if (ctx->return_valid != AUDITSC_INVALID) + audit_log_format(ab, " success=%s exit=%ld", + (ctx->return_valid == AUDITSC_SUCCESS ? + "yes" : "no"), + ctx->return_code); + audit_log_format(ab, + " items=%d" + " ppid=%d pid=%d uid=%u gid=%u euid=%u suid=%u" + " fsuid=%u egid=%u sgid=%u fsgid=%u", + ctx->name_count, + task_ppid_nr(current), task_tgid_nr(current), + from_kuid(&init_user_ns, cred->uid), + from_kgid(&init_user_ns, cred->gid), + from_kuid(&init_user_ns, cred->euid), + from_kuid(&init_user_ns, cred->suid), + from_kuid(&init_user_ns, cred->fsuid), + from_kgid(&init_user_ns, cred->egid), + from_kgid(&init_user_ns, cred->sgid), + from_kgid(&init_user_ns, cred->fsgid)); + audit_log_task_context(ab); + audit_log_key(ab, ctx->filterkey); + audit_log_end(ab); +} + static void audit_log_exit(void) { int i, call_panic = 0; @@ -1581,6 +1645,9 @@ static void audit_log_exit(void) audit_log_key(ab, context->filterkey); audit_log_end(ab); break; + case AUDIT_CTX_URING: + audit_log_uring(context); + break; default: BUG(); break; @@ -1751,6 +1818,105 @@ static void audit_return_fixup(struct audit_context *ctx, ctx->return_valid = (success ? AUDITSC_SUCCESS : AUDITSC_FAILURE); } +/** + * __audit_uring_entry - prepare the kernel task's audit context for io_uring + * @op: the io_uring opcode + * + * This is similar to audit_syscall_entry() but is intended for use by io_uring + * operations. This function should only ever be called from + * audit_uring_entry() as we rely on the audit context checking present in that + * function. + */ +void __audit_uring_entry(u8 op) +{ + struct audit_context *ctx = audit_context(); + + if (ctx->state == AUDIT_STATE_DISABLED) + return; + + /* + * NOTE: It's possible that we can be called from the process' context + * before it returns to userspace, and before audit_syscall_exit() + * is called. In this case there is not much to do, just record + * the io_uring details and return. + */ + ctx->uring_op = op; + if (ctx->context == AUDIT_CTX_SYSCALL) + return; + + ctx->dummy = !audit_n_rules; + if (!ctx->dummy && ctx->state == AUDIT_STATE_BUILD) + ctx->prio = 0; + + ctx->context = AUDIT_CTX_URING; + ctx->current_state = ctx->state; + ktime_get_coarse_real_ts64(&ctx->ctime); +} + +/** + * __audit_uring_exit - wrap up the kernel task's audit context after io_uring + * @success: true/false value to indicate if the operation succeeded or not + * @code: operation return code + * + * This is similar to audit_syscall_exit() but is intended for use by io_uring + * operations. This function should only ever be called from + * audit_uring_exit() as we rely on the audit context checking present in that + * function. + */ +void __audit_uring_exit(int success, long code) +{ + struct audit_context *ctx = audit_context(); + + /* + * TODO: At some point we will likely want to filter on io_uring ops + * and other things similar to what we do for syscalls, but that + * is something for another day; just record what we can here. + */ + + if (ctx->context == AUDIT_CTX_SYSCALL) { + /* + * NOTE: See the note in __audit_uring_entry() about the case + * where we may be called from process context before we + * return to userspace via audit_syscall_exit(). In this + * case we simply emit a URINGOP record and bail, the + * normal syscall exit handling will take care of + * everything else. + * It is also worth mentioning that when we are called, + * the current process creds may differ from the creds + * used during the normal syscall processing; keep that + * in mind if/when we move the record generation code. + */ + + /* + * We need to filter on the syscall info here to decide if we + * should emit a URINGOP record. I know it seems odd but this + * solves the problem where users have a filter to block *all* + * syscall records in the "exit" filter; we want to preserve + * the behavior here. + */ + audit_filter_syscall(current, ctx); + audit_filter_inodes(current, ctx); + if (ctx->current_state != AUDIT_STATE_RECORD) + return; + + audit_log_uring(ctx); + return; + } + + /* this may generate CONFIG_CHANGE records */ + if (!list_empty(&ctx->killed_trees)) + audit_kill_trees(ctx); + + audit_filter_inodes(current, ctx); + if (ctx->current_state != AUDIT_STATE_RECORD) + goto out; + audit_return_fixup(ctx, success, code); + audit_log_exit(); + +out: + audit_reset_context(ctx); +} + /** * __audit_syscall_entry - fill in an audit record at syscall entry * @major: major syscall type (function)

On 2021-09-15 12:49, Paul Moore wrote: Looks good. Acked-by: Richard Guy Briggs <rgb(a)redhat.com&gt; - RGB -- Richard Guy Briggs <rgb(a)redhat.com&gt; Sr. S/W Engineer, Kernel Security, Base Operating Systems Remote, Ottawa, Red Hat Canada IRC: rgb, SunRaycer Voice: +1.647.777.2635, Internal: (81) 32635

Converting io_uring's anonymous inode to the secure anon inode API enables LSMs to enforce policy on the io_uring anonymous inodes if they chose to do so. This is an important first step towards providing the necessary mechanisms so that LSMs can apply security policy to io_uring operations. Signed-off-by: Paul Moore <paul(a)paul-moore.com&gt; --- v4: - no change v3: - no change v2: - no change v1: - initial draft --- fs/io_uring.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index 388754b24785..56cc9aba0d01 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -10155,8 +10155,8 @@ static struct file *io_uring_get_file(struct io_ring_ctx *ctx) return ERR_PTR(ret); #endif - file = anon_inode_getfile("[io_uring]", &io_uring_fops, ctx, - O_RDWR | O_CLOEXEC); + file = anon_inode_getfile_secure("[io_uring]", &io_uring_fops, ctx, + O_RDWR | O_CLOEXEC, NULL); #if defined(CONFIG_UNIX) if (IS_ERR(file)) { sock_release(ctx->ring_sock);

This patch implements two new io_uring access controls, specifically support for controlling the io_uring "personalities" and IORING_SETUP_SQPOLL. Controlling the sharing of io_urings themselves is handled via the normal file/inode labeling and sharing mechanisms. The io_uring { override_creds } permission restricts which domains the subject domain can use to override it's own credentials. Granting a domain the io_uring { override_creds } permission allows it to impersonate another domain in io_uring operations. The io_uring { sqpoll } permission restricts which domains can create asynchronous io_uring polling threads. This is important from a security perspective as operations queued by this asynchronous thread inherit the credentials of the thread creator by default; if an io_uring is shared across process/domain boundaries this could result in one domain impersonating another. Controlling the creation of sqpoll threads, and the sharing of io_urings across processes, allow policy authors to restrict the ability of one domain to impersonate another via io_uring. As a quick summary, this patch adds a new object class with two permissions: io_uring { override_creds sqpoll } These permissions can be seen in the two simple policy statements below: allow domA_t domB_t : io_uring { override_creds }; allow domA_t self : io_uring { sqpoll }; Signed-off-by: Paul Moore <paul(a)paul-moore.com&gt; --- v4: - no change v3: - removed work-in-progress warning from the description v2: - made the selinux_uring_* funcs static - removed the debugging code v1: - initial draft --- security/selinux/hooks.c | 34 ++++++++++++++++++++++++++++++++++ security/selinux/include/classmap.h | 2 ++ 2 files changed, 36 insertions(+) diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 6517f221d52c..012e8504ed9e 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -7111,6 +7111,35 @@ static int selinux_perf_event_write(struct perf_event *event) } #endif +#ifdef CONFIG_IO_URING +/** + * selinux_uring_override_creds - check the requested cred override + * @new: the target creds + * + * Check to see if the current task is allowed to override it's credentials + * to service an io_uring operation. + */ +static int selinux_uring_override_creds(const struct cred *new) +{ + return avc_has_perm(&selinux_state, current_sid(), cred_sid(new), + SECCLASS_IO_URING, IO_URING__OVERRIDE_CREDS, NULL); +} + +/** + * selinux_uring_sqpoll - check if a io_uring polling thread can be created + * + * Check to see if the current task is allowed to create a new io_uring + * kernel polling thread. + */ +static int selinux_uring_sqpoll(void) +{ + int sid = current_sid(); + + return avc_has_perm(&selinux_state, sid, sid, + SECCLASS_IO_URING, IO_URING__SQPOLL, NULL); +} +#endif /* CONFIG_IO_URING */ + /* * IMPORTANT NOTE: When adding new hooks, please be careful to keep this order: * 1. any hooks that don't belong to (2.) or (3.) below, @@ -7349,6 +7378,11 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = { LSM_HOOK_INIT(perf_event_write, selinux_perf_event_write), #endif +#ifdef CONFIG_IO_URING + LSM_HOOK_INIT(uring_override_creds, selinux_uring_override_creds), + LSM_HOOK_INIT(uring_sqpoll, selinux_uring_sqpoll), +#endif + LSM_HOOK_INIT(locked_down, selinux_lockdown), /* diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h index 084757ff4390..698ccfdaf82d 100644 --- a/security/selinux/include/classmap.h +++ b/security/selinux/include/classmap.h @@ -254,6 +254,8 @@ struct security_class_mapping secclass_map[] = { { "integrity", "confidentiality", NULL } }, { "anon_inode", { COMMON_FILE_PERMS, NULL } }, + { "io_uring", + { "override_creds", "sqpoll", NULL } }, { NULL } };