linux-kernel - Re: [PATCH -next] fs/ntfs3: Don't use uni1 uninitialized in ntfs_d

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Message-ID: <CAKwvOdm=ZHjoF+j+ivj17t3OMpTA-5Dx71+g3KRSHO=L6RRpEA@mail.gmail.com>
Date:   Tue, 4 Oct 2022 15:56:45 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Konstantin Komarov <almaz.alexandrovich@...agon-software.com>,
        Tom Rix <trix@...hat.com>, ntfs3@...ts.linux.dev,
        llvm@...ts.linux.dev, patches@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] fs/ntfs3: Don't use uni1 uninitialized in ntfs_d_compare()

On Tue, Oct 4, 2022 at 7:42 AM Nathan Chancellor <nathan@...nel.org> wrote:
>
> Clang warns:
>
>   fs/ntfs3/namei.c:445:7: error: variable 'uni1' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>                   if (toupper(c1) != toupper(c2)) {
>                       ^~~~~~~~~~~~~~~~~~~~~~~~~~
>   ./include/linux/ctype.h:64:20: note: expanded from macro 'toupper'
>   #define toupper(c) __toupper(c)
>                     ^
>   fs/ntfs3/namei.c:487:12: note: uninitialized use occurs here
>           __putname(uni1);
>                     ^~~~
>   ./include/linux/fs.h:2789:65: note: expanded from macro '__putname'
>   #define __putname(name)         kmem_cache_free(names_cachep, (void *)(name))
>                                                                         ^~~~
>   fs/ntfs3/namei.c:445:3: note: remove the 'if' if its condition is always false
>                   if (toupper(c1) != toupper(c2)) {
>                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   fs/ntfs3/namei.c:434:7: error: variable 'uni1' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>                   if (!lm--) {
>                       ^~~~~
>   fs/ntfs3/namei.c:487:12: note: uninitialized use occurs here
>           __putname(uni1);
>                     ^~~~
>   ./include/linux/fs.h:2789:65: note: expanded from macro '__putname'
>   #define __putname(name)         kmem_cache_free(names_cachep, (void *)(name))
>                                                                         ^~~~
>   fs/ntfs3/namei.c:434:3: note: remove the 'if' if its condition is always false
>                   if (!lm--) {
>                   ^~~~~~~~~~~~
>   fs/ntfs3/namei.c:430:22: note: initialize the variable 'uni1' to silence this warning
>           struct cpu_str *uni1, *uni2;
>                               ^
>                               = NULL
>   2 errors generated.
>
> There is no point in calling __putname() in these particular error
> paths, as there has been no corresponding __getname() call yet. Just
> return directly in these blocks to clear up the warning.
>
> Fixes: a3a956c78efa ("fs/ntfs3: Add option "nocase"")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1729
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>  fs/ntfs3/namei.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/fs/ntfs3/namei.c b/fs/ntfs3/namei.c
> index 315763eb05ff..5d3a6ce3f05f 100644
> --- a/fs/ntfs3/namei.c
> +++ b/fs/ntfs3/namei.c
> @@ -431,10 +431,8 @@ static int ntfs_d_compare(const struct dentry *dentry, unsigned int len1,
>
>         /* First try fast implementation. */
>         for (;;) {
> -               if (!lm--) {
> -                       ret = len1 == len2 ? 0 : 1;
> -                       goto out;
> -               }
> +               if (!lm--)
> +                       return len1 == len2 ? 0 : 1;

I know the code originally used this, but I can't help but look at
this and think that it should be:

return len1 != len2;

Do you mind cleaning it up while you're here?

Otherwise LGTM;

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

You may retain my RB tag whether you send that suggestion in a v2 or not.

>
>                 if ((c1 = *n1++) == (c2 = *n2++))
>                         continue;
> @@ -442,10 +440,8 @@ static int ntfs_d_compare(const struct dentry *dentry, unsigned int len1,
>                 if (c1 >= 0x80 || c2 >= 0x80)
>                         break;
>
> -               if (toupper(c1) != toupper(c2)) {
> -                       ret = 1;
> -                       goto out;
> -               }
> +               if (toupper(c1) != toupper(c2))
> +                       return 1;
>         }
>
>         /*
>
> base-commit: d45da67caedacd500879de5e649360cc70777af7
> --
> 2.37.3
>


-- 
Thanks,
~Nick Desaulniers