[PATCH] erofs-utils: zero directory writer buffer

[PATCH] erofs-utils: zero directory writer buffer

[Garv]

Signed-off-by: Garv <garvkumar1502@gmail.com>
---
 lib/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/inode.c b/lib/inode.c
index ec96556..e7d07e0 100644
--- a/lib/inode.c
+++ b/lib/inode.c
@@ -597,7 +597,7 @@ static struct erofs_vfile *erofs_dirwriter_open(struct erofs_inode *dir)
 {
 	struct erofs_dirwriter_vf *dwv;
 
-	dwv = malloc(sizeof(*dwv) + erofs_blksiz(dir->sbi));
+	dwv = calloc(1, sizeof(*dwv) + erofs_blksiz(dir->sbi));
 	if (!dwv)
 		return ERR_PTR(-ENOMEM);
 	dwv->vf.ops = &erofs_dirwriter_vfops;
-- 
2.53.0

Re: [PATCH] erofs-utils: zero directory writer buffer

[Gao Xiang]

On Tue, Sep 29, 2026 at 07:09:17PM +0530, Garv wrote:
> Signed-off-by: Garv <garvkumar1502@gmail.com>

Can you explain a bit more why we need that?

Thanks,
Gao Xiang

> ---
>  lib/inode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/inode.c b/lib/inode.c
> index ec96556..e7d07e0 100644
> --- a/lib/inode.c
> +++ b/lib/inode.c
> @@ -597,7 +597,7 @@ static struct erofs_vfile *erofs_dirwriter_open(struct erofs_inode *dir)
>  {
>  	struct erofs_dirwriter_vf *dwv;
>  
> -	dwv = malloc(sizeof(*dwv) + erofs_blksiz(dir->sbi));
> +	dwv = calloc(1, sizeof(*dwv) + erofs_blksiz(dir->sbi));
>  	if (!dwv)
>  		return ERR_PTR(-ENOMEM);
>  	dwv->vf.ops = &erofs_dirwriter_vfops;
> -- 
> 2.53.0
> 
> 

Re: [PATCH] erofs-utils: zero directory writer buffer

[Garv Kumar]

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Hi Gao,

Thanks for asking. I traced the directory writer path again, and I agree
that my original explanation was incomplete. fill_dirblock() already clears
the unused portion of the generated directory block, so I shouldn’t have
described the change simply as fixing uninitialized directory-block spare
space.

The reproducer I used preserves non-zero contents in the output file by
bypassing the normal truncation path, and the calloc() change makes the
generated image deterministic in that test. However, I have not yet
established that dwv->dirdata is the source of those stale bytes, so I
don’t want to claim that this is the correct fix without further
verification.

I’ll investigate the exact data path and send a revised patch if necessary.

Thanks,
Garv

On Tue, 29 Sept 2026 at 19:12, Gao Xiang <xiang@kernel.org> wrote:

> On Tue, Sep 29, 2026 at 07:09:17PM +0530, Garv wrote:
> > Signed-off-by: Garv <garvkumar1502@gmail.com>
>
> Can you explain a bit more why we need that?
>
> Thanks,
> Gao Xiang
>
> > ---
> >  lib/inode.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/lib/inode.c b/lib/inode.c
> > index ec96556..e7d07e0 100644
> > --- a/lib/inode.c
> > +++ b/lib/inode.c
> > @@ -597,7 +597,7 @@ static struct erofs_vfile
> *erofs_dirwriter_open(struct erofs_inode *dir)
> >  {
> >       struct erofs_dirwriter_vf *dwv;
> >
> > -     dwv = malloc(sizeof(*dwv) + erofs_blksiz(dir->sbi));
> > +     dwv = calloc(1, sizeof(*dwv) + erofs_blksiz(dir->sbi));
> >       if (!dwv)
> >               return ERR_PTR(-ENOMEM);
> >       dwv->vf.ops = &erofs_dirwriter_vfops;
> > --
> > 2.53.0
> >
> >
>

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Re: [PATCH] erofs-utils: zero directory writer buffer

[Garv Kumar]

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Hi Gao,

Thanks for asking. I traced the directory writer path again, and I agree
that my original explanation was incomplete. fill_dirblock() already clears
the unused portion of the generated directory block, so I shouldn’t have
described the change simply as fixing uninitialized directory-block spare
space.

The reproducer I used preserves non-zero contents in the output file by
bypassing the normal truncation path, and the calloc() change makes the
generated image deterministic in that test. However, I have not yet
established that dwv->dirdata is the source of those stale bytes, so I
don’t want to claim that this is the correct fix without further
verification.

I’ll investigate the exact data path and send a revised patch if necessary.

Thanks,
Garv

On Tue, 29 Sept 2026 at 19:12, Gao Xiang <xiang@kernel.org> wrote:

> On Tue, Sep 29, 2026 at 07:09:17PM +0530, Garv wrote:
> > Signed-off-by: Garv <garvkumar1502@gmail.com>
>
> Can you explain a bit more why we need that?
>
> Thanks,
> Gao Xiang
>
> > ---
> >  lib/inode.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/lib/inode.c b/lib/inode.c
> > index ec96556..e7d07e0 100644
> > --- a/lib/inode.c
> > +++ b/lib/inode.c
> > @@ -597,7 +597,7 @@ static struct erofs_vfile
> *erofs_dirwriter_open(struct erofs_inode *dir)
> >  {
> >       struct erofs_dirwriter_vf *dwv;
> >
> > -     dwv = malloc(sizeof(*dwv) + erofs_blksiz(dir->sbi));
> > +     dwv = calloc(1, sizeof(*dwv) + erofs_blksiz(dir->sbi));
> >       if (!dwv)
> >               return ERR_PTR(-ENOMEM);
> >       dwv->vf.ops = &erofs_dirwriter_vfops;
> > --
> > 2.53.0
> >
> >
>

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