linux-kernel - Re: [PATCH -next] fanotify: Fix the checks in fanotify_fsid

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Message-ID: <CAKwvOdkHSRZy_BjyWx2sdZ89CwmMaHAJrNf_xmiGQDphrqjEiA@mail.gmail.com>
Date:   Fri, 27 Mar 2020 10:26:34 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Jan Kara <jack@...e.cz>, Amir Goldstein <amir73il@...il.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH -next] fanotify: Fix the checks in fanotify_fsid_equal

On Fri, Mar 27, 2020 at 10:10 AM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> Clang warns:
>
> fs/notify/fanotify/fanotify.c:28:23: warning: self-comparison always
> evaluates to true [-Wtautological-compare]
>         return fsid1->val[0] == fsid1->val[0] && fsid2->val[1] == fsid2->val[1];
>                              ^
> fs/notify/fanotify/fanotify.c:28:57: warning: self-comparison always
> evaluates to true [-Wtautological-compare]
>         return fsid1->val[0] == fsid1->val[0] && fsid2->val[1] == fsid2->val[1];
>                                                                ^
> 2 warnings generated.
>
> The intention was clearly to compare val[0] and val[1] in the two
> different fsid structs. Fix it otherwise this function always returns
> true.
>
> Fixes: afc894c784c8 ("fanotify: Store fanotify handles differently")
> Link: https://github.com/ClangBuiltLinux/linux/issues/952
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>

Thanks for the patch. Subtle bugs that are off by one character have
always been hard for me to spot!
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>  fs/notify/fanotify/fanotify.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> index 7a889da1ee12..cb54ecdb3fb9 100644
> --- a/fs/notify/fanotify/fanotify.c
> +++ b/fs/notify/fanotify/fanotify.c
> @@ -25,7 +25,7 @@ static bool fanotify_path_equal(struct path *p1, struct path *p2)
>  static inline bool fanotify_fsid_equal(__kernel_fsid_t *fsid1,
>                                        __kernel_fsid_t *fsid2)
>  {
> -       return fsid1->val[0] == fsid1->val[0] && fsid2->val[1] == fsid2->val[1];
> +       return fsid1->val[0] == fsid2->val[0] && fsid1->val[1] == fsid2->val[1];
>  }
>
>  static bool fanotify_fh_equal(struct fanotify_fh *fh1,
> --

-- 
Thanks,
~Nick Desaulniers