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

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Date:   Tue, 4 Oct 2022 16:26:10 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
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 04, 2022 at 03:56:45PM -0700, Nick Desaulniers wrote:
> 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.

I sent a v2 but I kept the changes separate:

https://lore.kernel.org/20221004232359.285685-1-nathan@kernel.org/
https://lore.kernel.org/20221004232359.285685-2-nathan@kernel.org/

Thanks for taking a look!

> >
> >                 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