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tomoyo: Use atomic_t for statistics counter

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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>
This commit is contained in:
Tetsuo Handa 2020-01-02 12:53:49 +09:00 committed by Greg Kroah-Hartman
parent ddba92fa83
commit 8f1c7fe1d5
1 changed files with 4 additions and 7 deletions
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11
security/tomoyo/common.c
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@ -2254,9 +2254,9 @@ static const char * const tomoyo_memory_headers[TOMOYO_MAX_MEMORY_STAT] = {
[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];
/**
@ -2268,10 +2268,7 @@ static time64_t tomoyo_stat_modified[TOMOYO_MAX_POLICY_STAT];
*/
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();
}
@ -2291,7 +2288,7 @@ static void tomoyo_read_stat(struct tomoyo_io_buffer *head)
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;
tomoyo_convert_time(tomoyo_stat_modified[i], &stamp);