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    Subject[PATCH 4.19 20/70] tomoyo: Use atomic_t for statistics counter
    Date
    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
    @@ -2254,9 +2254,9 @@ 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];

    /**
    @@ -2268,10 +2268,7 @@ 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();
    }

    @@ -2291,7 +2288,7 @@ 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;
    tomoyo_convert_time(tomoyo_stat_modified[i], &stamp);

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