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Subject[PATCH 19/37] binder: use atomic for transaction_log index
Date
The log->next index for the transaction log was
not protected when incremented. This led to a
case where log->next++ resulted in an index
larger than ARRAY_SIZE(log->entry) and eventually
a bad access to memory.

Fixed by making the log index an atomic64 and
converting to an array by using "% ARRAY_SIZE(log->entry)"

Also added "complete" field to the log entry which is
written last to tell the print code whether the
entry is complete

Signed-off-by: Todd Kjos <tkjos@google.com>
---
drivers/android/binder.c | 75 +++++++++++++++++++++++++++++++++++++-----------
1 file changed, 59 insertions(+), 16 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index a1912a22c89c..cb78a4e6872d 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -187,6 +187,7 @@ static inline void binder_stats_created(enum binder_stat_types type)

struct binder_transaction_log_entry {
int debug_id;
+ int debug_id_done;
int call_type;
int from_proc;
int from_thread;
@@ -202,8 +203,8 @@ struct binder_transaction_log_entry {
const char *context_name;
};
struct binder_transaction_log {
- int next;
- int full;
+ atomic_t cur;
+ bool full;
struct binder_transaction_log_entry entry[32];
};
static struct binder_transaction_log binder_transaction_log;
@@ -213,14 +214,19 @@ static struct binder_transaction_log_entry *binder_transaction_log_add(
struct binder_transaction_log *log)
{
struct binder_transaction_log_entry *e;
+ unsigned int cur = atomic_inc_return(&log->cur);

- e = &log->entry[log->next];
- memset(e, 0, sizeof(*e));
- log->next++;
- if (log->next == ARRAY_SIZE(log->entry)) {
- log->next = 0;
+ if (cur >= ARRAY_SIZE(log->entry))
log->full = 1;
- }
+ e = &log->entry[cur % ARRAY_SIZE(log->entry)];
+ WRITE_ONCE(e->debug_id_done, 0);
+ /*
+ * write-barrier to synchronize access to e->debug_id_done.
+ * We make sure the initialized 0 value is seen before
+ * memset() other fields are zeroed by memset.
+ */
+ smp_wmb();
+ memset(e, 0, sizeof(*e));
return e;
}

@@ -1400,8 +1406,10 @@ static void binder_transaction(struct binder_proc *proc,
struct binder_buffer_object *last_fixup_obj = NULL;
binder_size_t last_fixup_min_off = 0;
struct binder_context *context = proc->context;
+ int t_debug_id = atomic_inc_return(&binder_last_id);

e = binder_transaction_log_add(&binder_transaction_log);
+ e->debug_id = t_debug_id;
e->call_type = reply ? 2 : !!(tr->flags & TF_ONE_WAY);
e->from_proc = proc->pid;
e->from_thread = thread->pid;
@@ -1545,8 +1553,7 @@ static void binder_transaction(struct binder_proc *proc,
}
binder_stats_created(BINDER_STAT_TRANSACTION_COMPLETE);

- t->debug_id = atomic_inc_return(&binder_last_id);
- e->debug_id = t->debug_id;
+ t->debug_id = t_debug_id;

if (reply)
binder_debug(BINDER_DEBUG_TRANSACTION,
@@ -1821,6 +1828,12 @@ static void binder_transaction(struct binder_proc *proc,
else
wake_up_interruptible(target_wait);
}
+ /*
+ * write barrier to synchronize with initialization
+ * of log entry
+ */
+ smp_wmb();
+ WRITE_ONCE(e->debug_id_done, t_debug_id);
return;

err_translate_failed:
@@ -1858,6 +1871,13 @@ static void binder_transaction(struct binder_proc *proc,
e->return_error_line = return_error_line;
fe = binder_transaction_log_add(&binder_transaction_log_failed);
*fe = *e;
+ /*
+ * write barrier to synchronize with initialization
+ * of log entry
+ */
+ smp_wmb();
+ WRITE_ONCE(e->debug_id_done, t_debug_id);
+ WRITE_ONCE(fe->debug_id_done, t_debug_id);
}

BUG_ON(thread->return_error != BR_OK);
@@ -3718,27 +3738,47 @@ static int binder_proc_show(struct seq_file *m, void *unused)
static void print_binder_transaction_log_entry(struct seq_file *m,
struct binder_transaction_log_entry *e)
{
+ int debug_id = READ_ONCE(e->debug_id_done);
+ /*
+ * read barrier to guarantee debug_id_done read before
+ * we print the log values
+ */
+ smp_rmb();
seq_printf(m,
- "%d: %s from %d:%d to %d:%d context %s node %d handle %d size %d:%d ret %d/%d l=%d\n",
+ "%d: %s from %d:%d to %d:%d context %s node %d handle %d size %d:%d ret %d/%d l=%d",
e->debug_id, (e->call_type == 2) ? "reply" :
((e->call_type == 1) ? "async" : "call "), e->from_proc,
e->from_thread, e->to_proc, e->to_thread, e->context_name,
e->to_node, e->target_handle, e->data_size, e->offsets_size,
e->return_error, e->return_error_param,
e->return_error_line);
+ /*
+ * read-barrier to guarantee read of debug_id_done after
+ * done printing the fields of the entry
+ */
+ smp_rmb();
+ seq_printf(m, debug_id && debug_id == READ_ONCE(e->debug_id_done) ?
+ "\n" : " (incomplete)\n");
}

static int binder_transaction_log_show(struct seq_file *m, void *unused)
{
struct binder_transaction_log *log = m->private;
+ unsigned int log_cur = atomic_read(&log->cur);
+ unsigned int count;
+ unsigned int cur;
int i;

- if (log->full) {
- for (i = log->next; i < ARRAY_SIZE(log->entry); i++)
- print_binder_transaction_log_entry(m, &log->entry[i]);
+ count = log_cur + 1;
+ cur = count < ARRAY_SIZE(log->entry) && !log->full ?
+ 0 : count % ARRAY_SIZE(log->entry);
+ if (count > ARRAY_SIZE(log->entry) || log->full)
+ count = ARRAY_SIZE(log->entry);
+ for (i = 0; i < count; i++) {
+ unsigned int index = cur++ % ARRAY_SIZE(log->entry);
+
+ print_binder_transaction_log_entry(m, &log->entry[index]);
}
- for (i = 0; i < log->next; i++)
- print_binder_transaction_log_entry(m, &log->entry[i]);
return 0;
}

@@ -3793,6 +3833,9 @@ static int __init binder_init(void)
struct binder_device *device;
struct hlist_node *tmp;

+ atomic_set(&binder_transaction_log.cur, ~0U);
+ atomic_set(&binder_transaction_log_failed.cur, ~0U);
+
binder_debugfs_dir_entry_root = debugfs_create_dir("binder", NULL);
if (binder_debugfs_dir_entry_root)
binder_debugfs_dir_entry_proc = debugfs_create_dir("proc",
--
2.13.2.725.g09c95d1e9-goog
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