From: Steven Rostedt <rostedt@goodmis.org> stable inclusion from stable-v6.6.70 commit f452f397f9a6a605989e4151078ab76b41d490cc category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/IBJ835 CVE: NA Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit afd2627f727b89496d79a6b934a025fc916d4ded ] The TP_printk() portion of a trace event is executed at the time a event is read from the trace. This can happen seconds, minutes, hours, days, months, years possibly later since the event was recorded. If the print format contains a dereference to a string via "%s", and that string was allocated, there's a chance that string could be freed before it is read by the trace file. To protect against such bugs, there are two functions that verify the event. The first one is test_event_printk(), which is called when the event is created. It reads the TP_printk() format as well as its arguments to make sure nothing may be dereferencing a pointer that was not copied into the ring buffer along with the event. If it is, it will trigger a WARN_ON(). For strings that use "%s", it is not so easy. The string may not reside in the ring buffer but may still be valid. Strings that are static and part of the kernel proper which will not be freed for the life of the running system, are safe to dereference. But to know if it is a pointer to a static string or to something on the heap can not be determined until the event is triggered. This brings us to the second function that tests for the bad dereferencing of strings, trace_check_vprintf(). It would walk through the printf format looking for "%s", and when it finds it, it would validate that the pointer is safe to read. If not, it would produces a WARN_ON() as well and write into the ring buffer "[UNSAFE-MEMORY]". The problem with this is how it used va_list to have vsnprintf() handle all the cases that it didn't need to check. Instead of re-implementing vsnprintf(), it would make a copy of the format up to the %s part, and call vsnprintf() with the current va_list ap variable, where the ap would then be ready to point at the string in question. For architectures that passed va_list by reference this was possible. For architectures that passed it by copy it was not. A test_can_verify() function was used to differentiate between the two, and if it wasn't possible, it would disable it. Even for architectures where this was feasible, it was a stretch to rely on such a method that is undocumented, and could cause issues later on with new optimizations of the compiler. Instead, the first function test_event_printk() was updated to look at "%s" as well. If the "%s" argument is a pointer outside the event in the ring buffer, it would find the field type of the event that is the problem and mark the structure with a new flag called "needs_test". The event itself will be marked by TRACE_EVENT_FL_TEST_STR to let it be known that this event has a field that needs to be verified before the event can be printed using the printf format. When the event fields are created from the field type structure, the fields would copy the field type's "needs_test" value. Finally, before being printed, a new function ignore_event() is called which will check if the event has the TEST_STR flag set (if not, it returns false). If the flag is set, it then iterates through the events fields looking for the ones that have the "needs_test" flag set. Then it uses the offset field from the field structure to find the pointer in the ring buffer event. It runs the tests to make sure that pointer is safe to print and if not, it triggers the WARN_ON() and also adds to the trace output that the event in question has an unsafe memory access. The ignore_event() makes the trace_check_vprintf() obsolete so it is removed. Link: https://lore.kernel.org/all/CAHk-=wh3uOnqnZPpR0PeLZZtyWbZLboZ7cHLCKRWsocvs9Y... Cc: stable@vger.kernel.org Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Al Viro <viro@ZenIV.linux.org.uk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: https://lore.kernel.org/20241217024720.848621576@goodmis.org Fixes: 5013f454a352c ("tracing: Add check of trace event print fmts for dereferencing pointers") Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> Signed-off-by: Sasha Levin <sashal@kernel.org> Conflicts: include/linux/trace_events.h kernel/trace/trace.c [ 1. Conflicts caused by KABI reservation of the ftrace_event_field structure. 2. On LTS-6.6, the modifications of the following dependency patches will be reverted by the current patch: - 680c07fabc2b ("tracing: Handle old buffer mappings for event strings and functions") - 55841e8820b9 ("tracing: Fix trace_check_vprintf() when tp_printk is used") And merging these two patches would cause an individual commit to fail compilation. Therefore, we decided not to backport these patches and resolved the conflicts manually. ] Signed-off-by: Li Huafei <lihuafei1@huawei.com> --- include/linux/trace_events.h | 6 +- kernel/trace/trace.c | 214 +++++++++-------------------------- kernel/trace/trace.h | 6 +- kernel/trace/trace_events.c | 32 ++++-- kernel/trace/trace_output.c | 6 +- 5 files changed, 91 insertions(+), 173 deletions(-) diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h index 54ade3cea56e..e6cb294f03b4 100644 --- a/include/linux/trace_events.h +++ b/include/linux/trace_events.h @@ -280,7 +280,8 @@ struct trace_event_fields { const char *name; const int size; const int align; - const int is_signed; + const unsigned int is_signed:1; + unsigned int needs_test:1; const int filter_type; const int len; }; @@ -332,6 +333,7 @@ enum { TRACE_EVENT_FL_EPROBE_BIT, TRACE_EVENT_FL_FPROBE_BIT, TRACE_EVENT_FL_CUSTOM_BIT, + TRACE_EVENT_FL_TEST_STR_BIT, }; /* @@ -349,6 +351,7 @@ enum { * CUSTOM - Event is a custom event (to be attached to an exsiting tracepoint) * This is set when the custom event has not been attached * to a tracepoint yet, then it is cleared when it is. + * TEST_STR - The event has a "%s" that points to a string outside the event */ enum { TRACE_EVENT_FL_FILTERED = (1 << TRACE_EVENT_FL_FILTERED_BIT), @@ -362,6 +365,7 @@ enum { TRACE_EVENT_FL_EPROBE = (1 << TRACE_EVENT_FL_EPROBE_BIT), TRACE_EVENT_FL_FPROBE = (1 << TRACE_EVENT_FL_FPROBE_BIT), TRACE_EVENT_FL_CUSTOM = (1 << TRACE_EVENT_FL_CUSTOM_BIT), + TRACE_EVENT_FL_TEST_STR = (1 << TRACE_EVENT_FL_TEST_STR_BIT), }; #define TRACE_EVENT_FL_UKPROBE (TRACE_EVENT_FL_KPROBE | TRACE_EVENT_FL_UPROBE) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 88027b3b8158..10aace4d26e7 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -3760,17 +3760,12 @@ char *trace_iter_expand_format(struct trace_iterator *iter) } /* Returns true if the string is safe to dereference from an event */ -static bool trace_safe_str(struct trace_iterator *iter, const char *str, - bool star, int len) +static bool trace_safe_str(struct trace_iterator *iter, const char *str) { unsigned long addr = (unsigned long)str; struct trace_event *trace_event; struct trace_event_call *event; - /* Ignore strings with no length */ - if (star && !len) - return true; - /* OK if part of the event data */ if ((addr >= (unsigned long)iter->ent) && (addr < (unsigned long)iter->ent + iter->ent_size)) @@ -3810,133 +3805,69 @@ static bool trace_safe_str(struct trace_iterator *iter, const char *str, return false; } -static DEFINE_STATIC_KEY_FALSE(trace_no_verify); - -static int test_can_verify_check(const char *fmt, ...) -{ - char buf[16]; - va_list ap; - int ret; - - /* - * The verifier is dependent on vsnprintf() modifies the va_list - * passed to it, where it is sent as a reference. Some architectures - * (like x86_32) passes it by value, which means that vsnprintf() - * does not modify the va_list passed to it, and the verifier - * would then need to be able to understand all the values that - * vsnprintf can use. If it is passed by value, then the verifier - * is disabled. - */ - va_start(ap, fmt); - vsnprintf(buf, 16, "%d", ap); - ret = va_arg(ap, int); - va_end(ap); - - return ret; -} - -static void test_can_verify(void) -{ - if (!test_can_verify_check("%d %d", 0, 1)) { - pr_info("trace event string verifier disabled\n"); - static_branch_inc(&trace_no_verify); - } -} - /** - * trace_check_vprintf - Check dereferenced strings while writing to the seq buffer + * ignore_event - Check dereferenced fields while writing to the seq buffer * @iter: The iterator that holds the seq buffer and the event being printed - * @fmt: The format used to print the event - * @ap: The va_list holding the data to print from @fmt. * - * This writes the data into the @iter->seq buffer using the data from - * @fmt and @ap. If the format has a %s, then the source of the string - * is examined to make sure it is safe to print, otherwise it will - * warn and print "[UNSAFE MEMORY]" in place of the dereferenced string - * pointer. + * At boot up, test_event_printk() will flag any event that dereferences + * a string with "%s" that does exist in the ring buffer. It may still + * be valid, as the string may point to a static string in the kernel + * rodata that never gets freed. But if the string pointer is pointing + * to something that was allocated, there's a chance that it can be freed + * by the time the user reads the trace. This would cause a bad memory + * access by the kernel and possibly crash the system. + * + * This function will check if the event has any fields flagged as needing + * to be checked at runtime and perform those checks. + * + * If it is found that a field is unsafe, it will write into the @iter->seq + * a message stating what was found to be unsafe. + * + * @return: true if the event is unsafe and should be ignored, + * false otherwise. */ -void trace_check_vprintf(struct trace_iterator *iter, const char *fmt, - va_list ap) +bool ignore_event(struct trace_iterator *iter) { - const char *p = fmt; - const char *str; - int i, j; + struct ftrace_event_field *field; + struct trace_event *trace_event; + struct trace_event_call *event; + struct list_head *head; + struct trace_seq *seq; + const void *ptr; - if (WARN_ON_ONCE(!fmt)) - return; + trace_event = ftrace_find_event(iter->ent->type); - if (static_branch_unlikely(&trace_no_verify)) - goto print; + seq = &iter->seq; - /* Don't bother checking when doing a ftrace_dump() */ - if (iter->fmt == static_fmt_buf) - goto print; + if (!trace_event) { + trace_seq_printf(seq, "EVENT ID %d NOT FOUND?\n", iter->ent->type); + return true; + } - while (*p) { - bool star = false; - int len = 0; - - j = 0; - - /* We only care about %s and variants */ - for (i = 0; p[i]; i++) { - if (i + 1 >= iter->fmt_size) { - /* - * If we can't expand the copy buffer, - * just print it. - */ - if (!trace_iter_expand_format(iter)) - goto print; - } + event = container_of(trace_event, struct trace_event_call, event); + if (!(event->flags & TRACE_EVENT_FL_TEST_STR)) + return false; - if (p[i] == '\\' && p[i+1]) { - i++; - continue; - } - if (p[i] == '%') { - /* Need to test cases like %08.*s */ - for (j = 1; p[i+j]; j++) { - if (isdigit(p[i+j]) || - p[i+j] == '.') - continue; - if (p[i+j] == '*') { - star = true; - continue; - } - break; - } - if (p[i+j] == 's') - break; - star = false; - } - j = 0; - } - /* If no %s found then just print normally */ - if (!p[i]) - break; + head = trace_get_fields(event); + if (!head) { + trace_seq_printf(seq, "FIELDS FOR EVENT '%s' NOT FOUND?\n", + trace_event_name(event)); + return true; + } - /* Copy up to the %s, and print that */ - strncpy(iter->fmt, p, i); - iter->fmt[i] = '\0'; - trace_seq_vprintf(&iter->seq, iter->fmt, ap); + /* Offsets are from the iter->ent that points to the raw event */ + ptr = iter->ent; - /* - * If iter->seq is full, the above call no longer guarantees - * that ap is in sync with fmt processing, and further calls - * to va_arg() can return wrong positional arguments. - * - * Ensure that ap is no longer used in this case. - */ - if (iter->seq.full) { - p = ""; - break; - } + list_for_each_entry(field, head, link) { + const char *str; + bool good; + + if (!field->needs_test) + continue; - if (star) - len = va_arg(ap, int); + str = *(const char **)(ptr + field->offset); - /* The ap now points to the string data of the %s */ - str = va_arg(ap, const char *); + good = trace_safe_str(iter, str); /* * If you hit this warning, it is likely that the @@ -3947,45 +3878,14 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt, * instead. See samples/trace_events/trace-events-sample.h * for reference. */ - if (WARN_ONCE(!trace_safe_str(iter, str, star, len), - "fmt: '%s' current_buffer: '%s'", - fmt, seq_buf_str(&iter->seq.seq))) { - int ret; - - /* Try to safely read the string */ - if (star) { - if (len + 1 > iter->fmt_size) - len = iter->fmt_size - 1; - if (len < 0) - len = 0; - ret = copy_from_kernel_nofault(iter->fmt, str, len); - iter->fmt[len] = 0; - star = false; - } else { - ret = strncpy_from_kernel_nofault(iter->fmt, str, - iter->fmt_size); - } - if (ret < 0) - trace_seq_printf(&iter->seq, "(0x%px)", str); - else - trace_seq_printf(&iter->seq, "(0x%px:%s)", - str, iter->fmt); - str = "[UNSAFE-MEMORY]"; - strcpy(iter->fmt, "%s"); - } else { - strncpy(iter->fmt, p + i, j + 1); - iter->fmt[j+1] = '\0'; + if (WARN_ONCE(!good, "event '%s' has unsafe pointer field '%s'", + trace_event_name(event), field->name)) { + trace_seq_printf(seq, "EVENT %s: HAS UNSAFE POINTER FIELD '%s'\n", + trace_event_name(event), field->name); + return true; } - if (star) - trace_seq_printf(&iter->seq, iter->fmt, len, str); - else - trace_seq_printf(&iter->seq, iter->fmt, str); - - p += i + j + 1; } - print: - if (*p) - trace_seq_vprintf(&iter->seq, p, ap); + return false; } const char *trace_event_format(struct trace_iterator *iter, const char *fmt) @@ -10533,8 +10433,6 @@ __init static int tracer_alloc_buffers(void) register_snapshot_cmd(); - test_can_verify(); - return 0; out_free_pipe_cpumask: diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 3ff785aa9444..2af084b67fa0 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -648,9 +648,8 @@ void trace_buffer_unlock_commit_nostack(struct trace_buffer *buffer, bool trace_is_tracepoint_string(const char *str); const char *trace_event_format(struct trace_iterator *iter, const char *fmt); -void trace_check_vprintf(struct trace_iterator *iter, const char *fmt, - va_list ap) __printf(2, 0); char *trace_iter_expand_format(struct trace_iterator *iter); +bool ignore_event(struct trace_iterator *iter); int trace_empty(struct trace_iterator *iter); @@ -1329,7 +1328,8 @@ struct ftrace_event_field { int filter_type; int offset; int size; - int is_signed; + unsigned int is_signed:1; + unsigned int needs_test:1; int len; KABI_RESERVE(1) KABI_RESERVE(2) diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 64cd856308e7..0b7eb6f230ed 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -82,7 +82,7 @@ static int system_refcount_dec(struct event_subsystem *system) } static struct ftrace_event_field * -__find_event_field(struct list_head *head, char *name) +__find_event_field(struct list_head *head, const char *name) { struct ftrace_event_field *field; @@ -114,7 +114,8 @@ trace_find_event_field(struct trace_event_call *call, char *name) static int __trace_define_field(struct list_head *head, const char *type, const char *name, int offset, int size, - int is_signed, int filter_type, int len) + int is_signed, int filter_type, int len, + int need_test) { struct ftrace_event_field *field; @@ -133,6 +134,7 @@ static int __trace_define_field(struct list_head *head, const char *type, field->offset = offset; field->size = size; field->is_signed = is_signed; + field->needs_test = need_test; field->len = len; list_add(&field->link, head); @@ -151,13 +153,13 @@ int trace_define_field(struct trace_event_call *call, const char *type, head = trace_get_fields(call); return __trace_define_field(head, type, name, offset, size, - is_signed, filter_type, 0); + is_signed, filter_type, 0, 0); } EXPORT_SYMBOL_GPL(trace_define_field); static int trace_define_field_ext(struct trace_event_call *call, const char *type, const char *name, int offset, int size, int is_signed, - int filter_type, int len) + int filter_type, int len, int need_test) { struct list_head *head; @@ -166,13 +168,13 @@ static int trace_define_field_ext(struct trace_event_call *call, const char *typ head = trace_get_fields(call); return __trace_define_field(head, type, name, offset, size, - is_signed, filter_type, len); + is_signed, filter_type, len, need_test); } #define __generic_field(type, item, filter_type) \ ret = __trace_define_field(&ftrace_generic_fields, #type, \ #item, 0, 0, is_signed_type(type), \ - filter_type, 0); \ + filter_type, 0, 0); \ if (ret) \ return ret; @@ -181,7 +183,8 @@ static int trace_define_field_ext(struct trace_event_call *call, const char *typ "common_" #item, \ offsetof(typeof(ent), item), \ sizeof(ent.item), \ - is_signed_type(type), FILTER_OTHER, 0); \ + is_signed_type(type), FILTER_OTHER, \ + 0, 0); \ if (ret) \ return ret; @@ -332,6 +335,7 @@ static bool process_pointer(const char *fmt, int len, struct trace_event_call *c /* Return true if the string is safe */ static bool process_string(const char *fmt, int len, struct trace_event_call *call) { + struct trace_event_fields *field; const char *r, *e, *s; e = fmt + len; @@ -372,8 +376,16 @@ static bool process_string(const char *fmt, int len, struct trace_event_call *ca if (process_pointer(fmt, len, call)) return true; - /* Make sure the field is found, and consider it OK for now if it is */ - return find_event_field(fmt, call) != NULL; + /* Make sure the field is found */ + field = find_event_field(fmt, call); + if (!field) + return false; + + /* Test this field's string before printing the event */ + call->flags |= TRACE_EVENT_FL_TEST_STR; + field->needs_test = 1; + + return true; } /* @@ -2552,7 +2564,7 @@ event_define_fields(struct trace_event_call *call) ret = trace_define_field_ext(call, field->type, field->name, offset, field->size, field->is_signed, field->filter_type, - field->len); + field->len, field->needs_test); if (WARN_ON_ONCE(ret)) { pr_err("error code is %d\n", ret); break; diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c index db575094c498..2b948d35fb59 100644 --- a/kernel/trace/trace_output.c +++ b/kernel/trace/trace_output.c @@ -317,10 +317,14 @@ EXPORT_SYMBOL(trace_raw_output_prep); void trace_event_printf(struct trace_iterator *iter, const char *fmt, ...) { + struct trace_seq *s = &iter->seq; va_list ap; + if (ignore_event(iter)) + return; + va_start(ap, fmt); - trace_check_vprintf(iter, trace_event_format(iter, fmt), ap); + trace_seq_vprintf(s, trace_event_format(iter, fmt), ap); va_end(ap); } EXPORT_SYMBOL(trace_event_printf); -- 2.25.1