[PATCH] ftrace: Fix use-after-free issue in ftrace_location()

[Zheng Yejian]

KASAN reports a bug:

  BUG: KASAN: use-after-free in ftrace_location+0x90/0x120
  Read of size 8 at addr ffff888141d40010 by task insmod/424
  CPU: 8 PID: 424 Comm: insmod Tainted: G        W          6.9.0-rc2+ #213
  [...]
  Call Trace:
   <TASK>
   dump_stack_lvl+0x68/0xa0
   print_report+0xcf/0x610
   kasan_report+0xb5/0xe0
   ftrace_location+0x90/0x120
   register_kprobe+0x14b/0xa40
   kprobe_init+0x2d/0xff0 [kprobe_example]
   do_one_initcall+0x8f/0x2d0
   do_init_module+0x13a/0x3c0
   load_module+0x3082/0x33d0
   init_module_from_file+0xd2/0x130
   __x64_sys_finit_module+0x306/0x440
   do_syscall_64+0x68/0x140
   entry_SYSCALL_64_after_hwframe+0x71/0x79

The root cause is that when lookup_rec() is lookuping ftrace record of
an address in some module, and at the same time in ftrace_release_mod(),
the memory that saving ftrace records has been freed as that module is
being deleted.

  register_kprobes() {
    check_kprobe_address_safe() {
      arch_check_ftrace_location() {
        ftrace_location() {
          lookup_rec()  // access memory that has been freed by
                        // ftrace_release_mod() !!!

It seems that the ftrace_lock is required when lookuping records in
ftrace_location(), so is ftrace_location_range().

Fixes: ae6aa16fdc16 ("kprobes: introduce ftrace based optimization")
Signed-off-by: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
---
 kernel/trace/ftrace.c | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index da1710499698..838d175709c1 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1581,7 +1581,7 @@ static struct dyn_ftrace *lookup_rec(unsigned long start, unsigned long end)
 }
 
 /**
- * ftrace_location_range - return the first address of a traced location
+ * ftrace_location_range_locked - return the first address of a traced location
  *	if it touches the given ip range
  * @start: start of range to search.
  * @end: end of range to search (inclusive). @end points to the last byte
@@ -1592,7 +1592,7 @@ static struct dyn_ftrace *lookup_rec(unsigned long start, unsigned long end)
  * that is either a NOP or call to the function tracer. It checks the ftrace
  * internal tables to determine if the address belongs or not.
  */
-unsigned long ftrace_location_range(unsigned long start, unsigned long end)
+static unsigned long ftrace_location_range_locked(unsigned long start, unsigned long end)
 {
 	struct dyn_ftrace *rec;
 
@@ -1603,6 +1603,17 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end)
 	return 0;
 }
 
+unsigned long ftrace_location_range(unsigned long start, unsigned long end)
+{
+	unsigned long loc;
+
+	mutex_lock(&ftrace_lock);
+	loc = ftrace_location_range_locked(start, end);
+	mutex_unlock(&ftrace_lock);
+
+	return loc;
+}
+
 /**
  * ftrace_location - return the ftrace location
  * @ip: the instruction pointer to check
@@ -1614,25 +1625,22 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end)
  */
 unsigned long ftrace_location(unsigned long ip)
 {
-	struct dyn_ftrace *rec;
+	unsigned long loc;
 	unsigned long offset;
 	unsigned long size;
 
-	rec = lookup_rec(ip, ip);
-	if (!rec) {
+	loc = ftrace_location_range(ip, ip);
+	if (!loc) {
 		if (!kallsyms_lookup_size_offset(ip, &size, &offset))
 			goto out;
 
 		/* map sym+0 to __fentry__ */
 		if (!offset)
-			rec = lookup_rec(ip, ip + size - 1);
+			loc = ftrace_location_range(ip, ip + size - 1);
 	}
 
-	if (rec)
-		return rec->ip;
-
 out:
-	return 0;
+	return loc;
 }
 
 /**
-- 
2.25.1