[PATCH 5.5 20/23] tomoyo: Use atomic_t for statistics counter

Greg Kroah-Hartman
2020-02-03T16:38:26Z

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

commit a8772fad0172aeae339144598b809fd8d4823331 upstream.

syzbot is reporting that there is a race at tomoyo_stat_update() [1].
Although it is acceptable to fail to track exact number of times policy
was updated, convert to atomic_t because this is not a hot path.

[1] https://syzkaller.appspot.com/bug?id=a4d7b973972eeed410596e6604580e0133b0fc04

Reported-by: syzbot <syzbot+efea72d4a0a1d03596cd@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
security/tomoyo/common.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)

--- a/security/tomoyo/common.c
+++ b/security/tomoyo/common.c
@@ -2322,9 +2322,9 @@ static const char * const tomoyo_memory_
[TOMOYO_MEMORY_QUERY] = "query message:",
};

-/* Timestamp counter for last updated. */
-static unsigned int tomoyo_stat_updated[TOMOYO_MAX_POLICY_STAT];
/* Counter for number of updates. */
+static atomic_t tomoyo_stat_updated[TOMOYO_MAX_POLICY_STAT];
+/* Timestamp counter for last updated. */
static time64_t tomoyo_stat_modified[TOMOYO_MAX_POLICY_STAT];

/**
@@ -2336,10 +2336,7 @@ static time64_t tomoyo_stat_modified[TOM
*/
void tomoyo_update_stat(const u8 index)
{
- /*
- * I don't use atomic operations because race condition is not fatal.
- */
- tomoyo_stat_updated[index]++;
+ atomic_inc(&tomoyo_stat_updated[index]);
tomoyo_stat_modified[index] = ktime_get_real_seconds();
}

@@ -2360,7 +2357,7 @@ static void tomoyo_read_stat(struct tomo
for (i = 0; i < TOMOYO_MAX_POLICY_STAT; i++) {
tomoyo_io_printf(head, "Policy %-30s %10u",
tomoyo_policy_headers[i],
- tomoyo_stat_updated[i]);
+ atomic_read(&tomoyo_stat_updated[i]));
if (tomoyo_stat_modified[i]) {
struct tomoyo_time stamp;