4f5359685a
I found that there is nothing to protect event_hash in
ftrace_find_event(). Rcu protects the event hashlist
but not the event itself while we use it after its extraction
through ftrace_find_event().
This lack of a proper locking in this spot opens a race
window between any event dereferencing and module removal.
Eg:
--Task A--
print_trace_line(trace) {
event = find_ftrace_event(trace)
--Task B--
trace_module_remove_events(mod) {
list_trace_events_module(ev, mod) {
unregister_ftrace_event(ev->event) {
hlist_del(ev->event->node)
list_del(....)
}
}
}
|--> module removed, the event has been dropped
--Task A--
event->print(trace); // Dereferencing freed memory
If the event retrieved belongs to a module and this module
is concurrently removed, we may end up dereferencing a data
from a freed module.
RCU could solve this, but it would add latency to the kernel and
forbid tracers output callbacks to call any sleepable code.
So this fix converts 'trace_event_mutex' to a read/write semaphore,
and adds trace_event_read_lock() to protect ftrace_find_event().
[ Impact: fix possible freed memory dereference in ftrace ]
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <4A114806.7090302@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
48 lines
1.4 KiB
C
48 lines
1.4 KiB
C
#ifndef __TRACE_EVENTS_H
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#define __TRACE_EVENTS_H
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#include <linux/trace_seq.h>
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#include "trace.h"
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extern enum print_line_t
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trace_print_bprintk_msg_only(struct trace_iterator *iter);
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extern enum print_line_t
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trace_print_printk_msg_only(struct trace_iterator *iter);
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extern int
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seq_print_ip_sym(struct trace_seq *s, unsigned long ip,
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unsigned long sym_flags);
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extern int seq_print_userip_objs(const struct userstack_entry *entry,
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struct trace_seq *s, unsigned long sym_flags);
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extern int seq_print_user_ip(struct trace_seq *s, struct mm_struct *mm,
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unsigned long ip, unsigned long sym_flags);
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extern int trace_print_context(struct trace_iterator *iter);
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extern int trace_print_lat_context(struct trace_iterator *iter);
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extern void trace_event_read_lock(void);
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extern void trace_event_read_unlock(void);
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extern struct trace_event *ftrace_find_event(int type);
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extern enum print_line_t trace_nop_print(struct trace_iterator *iter,
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int flags);
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#define MAX_MEMHEX_BYTES 8
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#define HEX_CHARS (MAX_MEMHEX_BYTES*2 + 1)
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#define SEQ_PUT_FIELD_RET(s, x) \
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do { \
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if (!trace_seq_putmem(s, &(x), sizeof(x))) \
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return TRACE_TYPE_PARTIAL_LINE; \
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} while (0)
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#define SEQ_PUT_HEX_FIELD_RET(s, x) \
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do { \
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BUILD_BUG_ON(sizeof(x) > MAX_MEMHEX_BYTES); \
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if (!trace_seq_putmem_hex(s, &(x), sizeof(x))) \
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return TRACE_TYPE_PARTIAL_LINE; \
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} while (0)
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#endif
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