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SubjectRe: [PATCH v8 11/12] user_events: Validate user payloads for size and null termination
On Thu, 16 Dec 2021 09:35:10 -0800
Beau Belgrave <beaub@linux.microsoft.com> wrote:

> Add validation to ensure data is at or greater than the min size for the
> fields of the event. If a dynamic array is used and is a type of char,
> ensure null termination of the array exists.

OK, looks good to me except a few nitpicks.

Reveiewed-by: Masami Hiramatsu <mhiramat@kernel.org>

I added some comments below.

>
> Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
> ---
> kernel/trace/trace_events_user.c | 147 +++++++++++++++++++++++++++----
> 1 file changed, 132 insertions(+), 15 deletions(-)
>
> diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> index fa3e26281fc3..58b8c9607c80 100644
> --- a/kernel/trace/trace_events_user.c
> +++ b/kernel/trace/trace_events_user.c
> @@ -64,9 +64,11 @@ struct user_event {
> struct dyn_event devent;
> struct hlist_node node;
> struct list_head fields;
> + struct list_head validators;
> atomic_t refcnt;
> int index;
> int flags;
> + int min_size;
> };
>
> /*
> @@ -81,8 +83,17 @@ struct user_event_refs {
> struct user_event *events[];
> };
>
> +#define VALIDATOR_ENSURE_NULL (1 << 0)
> +#define VALIDATOR_REL (1 << 1)
> +
> +struct user_event_validator {
> + struct list_head link;
> + int offset;
> + int flags;
> +};
> +
> typedef void (*user_event_func_t) (struct user_event *user, struct iov_iter *i,
> - void *tpdata);
> + void *tpdata, bool *faulted);

Why don't you just return "int" value? ;-)

>
> static int user_event_parse(char *name, char *args, char *flags,
> struct user_event **newuser);
> @@ -214,6 +225,17 @@ static int user_field_size(const char *type)
> return -EINVAL;
> }
>
> +static void user_event_destroy_validators(struct user_event *user)
> +{
> + struct user_event_validator *validator, *next;
> + struct list_head *head = &user->validators;
> +
> + list_for_each_entry_safe(validator, next, head, link) {
> + list_del(&validator->link);
> + kfree(validator);
> + }
> +}
> +
> static void user_event_destroy_fields(struct user_event *user)
> {
> struct ftrace_event_field *field, *next;
> @@ -229,13 +251,43 @@ static int user_event_add_field(struct user_event *user, const char *type,
> const char *name, int offset, int size,
> int is_signed, int filter_type)
> {
> + struct user_event_validator *validator;
> struct ftrace_event_field *field;
> + int validator_flags = 0;
>
> field = kmalloc(sizeof(*field), GFP_KERNEL);
>
> if (!field)
> return -ENOMEM;
>
> + if (str_has_prefix(type, "__data_loc "))
> + goto add_validator;
> +
> + if (str_has_prefix(type, "__rel_loc ")) {
> + validator_flags |= VALIDATOR_REL;
> + goto add_validator;
> + }
> +
> + goto add_field;
> +
> +add_validator:
> + if (strstr(type, "char") != 0)
> + validator_flags |= VALIDATOR_ENSURE_NULL;
> +
> + validator = kmalloc(sizeof(*validator), GFP_KERNEL);
> +
> + if (!validator) {
> + kfree(field);
> + return -ENOMEM;
> + }
> +
> + validator->flags = validator_flags;
> + validator->offset = offset;
> +
> + /* Want sequential access when validating */
> + list_add_tail(&validator->link, &user->validators);
> +
> +add_field:
> field->type = type;
> field->name = name;
> field->offset = offset;
> @@ -245,6 +297,12 @@ static int user_event_add_field(struct user_event *user, const char *type,
>
> list_add(&field->link, &user->fields);
>
> + /*
> + * Min size from user writes that are required, this does not include
> + * the size of trace_entry (common fields).
> + */
> + user->min_size = (offset + size) - sizeof(struct trace_entry);
> +
> return 0;
> }
>
> @@ -516,6 +574,7 @@ static int destroy_user_event(struct user_event *user)
> clear_bit(user->index, page_bitmap);
> hash_del(&user->node);
>
> + user_event_destroy_validators(user);
> kfree(user->call.print_fmt);
> kfree(EVENT_NAME(user));
> kfree(user);
> @@ -537,15 +596,49 @@ static struct user_event *find_user_event(char *name, u32 *outkey)
> return NULL;
> }
>
> +static int user_event_validate(struct user_event *user, void *data, int len)
> +{
> + struct list_head *head = &user->validators;
> + struct user_event_validator *validator;
> + void *pos, *end = data + len;
> + u32 loc, offset, size;
> +
> + list_for_each_entry(validator, head, link) {
> + pos = data + validator->offset;
> +
> + /* Already done min_size check, no bounds check here */
> + loc = *(u32 *)pos;
> + offset = loc & 0xffff;
> + size = loc >> 16;
> +
> + if (likely(validator->flags & VALIDATOR_REL))
> + pos += offset + sizeof(loc);
> + else
> + pos = data + offset;
> +
> + pos += size;
> +
> + if (unlikely(pos > end))
> + return -EFAULT;
> +
> + if (likely(validator->flags & VALIDATOR_ENSURE_NULL))
> + if (unlikely(*(char *)(pos - 1) != 0))

As we discussed in the previous version, isn't it '\0' ?
(just a style comment)

> + return -EFAULT;
> + }
> +
> + return 0;
> +}
> +
> /*
> * Writes the user supplied payload out to a trace file.
> */
> static void user_event_ftrace(struct user_event *user, struct iov_iter *i,
> - void *tpdata)
> + void *tpdata, bool *faulted)
> {
> struct trace_event_file *file;
> struct trace_entry *entry;
> struct trace_event_buffer event_buffer;
> + size_t size = sizeof(*entry) + i->count;
>
> file = (struct trace_event_file *)tpdata;
>
> @@ -555,19 +648,25 @@ static void user_event_ftrace(struct user_event *user, struct iov_iter *i,
> return;
>
> /* Allocates and fills trace_entry, + 1 of this is data payload */
> - entry = trace_event_buffer_reserve(&event_buffer, file,
> - sizeof(*entry) + i->count);
> + entry = trace_event_buffer_reserve(&event_buffer, file, size);
>
> if (unlikely(!entry))
> return;
>
> - if (unlikely(!copy_nofault(entry + 1, i->count, i))) {
> - __trace_event_discard_commit(event_buffer.buffer,
> - event_buffer.event);
> - return;
> - }
> + if (unlikely(!copy_nofault(entry + 1, i->count, i)))
> + goto discard;

OK, this is a fault error.

> +
> + if (!list_empty(&user->validators) &&
> + unlikely(user_event_validate(user, entry, size)))
> + goto discard;

But this maybe an invalid parameter error.

Thank you,

>
> trace_event_buffer_commit(&event_buffer);
> +
> + return;
> +discard:
> + *faulted = true;
> + __trace_event_discard_commit(event_buffer.buffer,
> + event_buffer.event);
> }
>
> #ifdef CONFIG_PERF_EVENTS
> @@ -622,7 +721,7 @@ static void user_event_bpf(struct user_event *user, struct iov_iter *i)
> * Writes the user supplied payload out to perf ring buffer or eBPF program.
> */
> static void user_event_perf(struct user_event *user, struct iov_iter *i,
> - void *tpdata)
> + void *tpdata, bool *faulted)
> {
> struct hlist_head *perf_head;
>
> @@ -645,14 +744,21 @@ static void user_event_perf(struct user_event *user, struct iov_iter *i,
>
> perf_fetch_caller_regs(regs);
>
> - if (unlikely(!copy_nofault(perf_entry + 1, i->count, i))) {
> - perf_swevent_put_recursion_context(context);
> - return;
> - }
> + if (unlikely(!copy_nofault(perf_entry + 1, i->count, i)))
> + goto discard;
> +
> + if (!list_empty(&user->validators) &&
> + unlikely(user_event_validate(user, perf_entry, size)))
> + goto discard;
>
> perf_trace_buf_submit(perf_entry, size, context,
> user->call.event.type, 1, regs,
> perf_head, NULL);
> +
> + return;
> +discard:
> + *faulted = true;
> + perf_swevent_put_recursion_context(context);
> }
> }
> #endif
> @@ -967,6 +1073,7 @@ static int user_event_parse(char *name, char *args, char *flags,
>
> INIT_LIST_HEAD(&user->class.fields);
> INIT_LIST_HEAD(&user->fields);
> + INIT_LIST_HEAD(&user->validators);
>
> user->tracepoint.name = name;
>
> @@ -1015,6 +1122,7 @@ static int user_event_parse(char *name, char *args, char *flags,
> return 0;
> put_user:
> user_event_destroy_fields(user);
> + user_event_destroy_validators(user);
> kfree(user);
> return ret;
> }
> @@ -1072,6 +1180,9 @@ static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
> if (unlikely(user == NULL))
> return -ENOENT;
>
> + if (unlikely(i->count < user->min_size))
> + return -EINVAL;
> +
> tp = &user->tracepoint;
>
> /*
> @@ -1083,10 +1194,13 @@ static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
> user_event_func_t probe_func;
> struct iov_iter copy;
> void *tpdata;
> + bool faulted;
>
> if (unlikely(iov_iter_fault_in_readable(i, i->count)))
> return -EFAULT;
>
> + faulted = false;
> +
> rcu_read_lock_sched();
>
> probe_func_ptr = rcu_dereference_sched(tp->funcs);
> @@ -1096,11 +1210,14 @@ static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
> copy = *i;
> probe_func = probe_func_ptr->func;
> tpdata = probe_func_ptr->data;
> - probe_func(user, &copy, tpdata);
> + probe_func(user, &copy, tpdata, &faulted);
> } while ((++probe_func_ptr)->func);
> }
>
> rcu_read_unlock_sched();
> +
> + if (unlikely(faulted))
> + return -EFAULT;
> }
>
> return ret;
> --
> 2.17.1
>


--
Masami Hiramatsu <mhiramat@kernel.org>

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