[PATCH -next] fanotify: Fix the checks in fanotify_fsid_equal

[PATCH -next] fanotify: Fix the checks in fanotify_fsid_equal

[Nathan Chancellor]

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@gmail.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,
-- 
2.26.0

Re: [PATCH -next] fanotify: Fix the checks in fanotify_fsid_equal

[Nick Desaulniers]

On Fri, Mar 27, 2020 at 10:10 AM Nathan Chancellor
<natechancellor@gmail.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@gmail.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@google.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

Re: [PATCH -next] fanotify: Fix the checks in fanotify_fsid_equal

[Amir Goldstein]

On Fri, Mar 27, 2020 at 8:10 PM Nathan Chancellor
<natechancellor@gmail.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@gmail.com>
> ---

Ouch! Good catch!

It would have been quite hard to catch this with tests as
non equal fsid and equal fid are quite rare in the wild.
I will try to write some test with mounts of cloned loop devs.

Thanks,
Amir.

Re: [PATCH -next] fanotify: Fix the checks in fanotify_fsid_equal

[Jan Kara]

On Fri 27-03-20 10:10:30, Nathan Chancellor 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@gmail.com>

Thanks for the fix! That's a good catch that would have been pain to debug!
I've applied it to my tree.

								Honza

> ---
>  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,
> -- 
> 2.26.0
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR