linux-kernel - Re: [PATCH] jffs2: Fix retry handling jffs2

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Message-ID: <CAHc6FU73Cx=KengB8R=am_d0fGvQjaRrog9tqBC8TJaa+F296g@mail.gmail.com>
Date:   Mon, 17 Dec 2018 14:42:16 +0100
From:   Andreas Gruenbacher <agruenba@...hat.com>
To:     Richard Weinberger <richard@....at>
Cc:     linux-mtd@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>,
        dwmw2@...radead.org, stable <stable@...r.kernel.org>
Subject: Re: [PATCH] jffs2: Fix retry handling jffs2_listxattr

Hi Richard,

On Sat, 15 Dec 2018 at 11:22, Richard Weinberger <richard@....at> wrote:
> When jffs2 has to retry reading xattrs we need to reset
> the buffer pointer. Otherwise we return old xattrs from the
> previous iteration which leads to a inconsistency between
> the number of bytes we return and the real list size.
>
> Cc: <stable@...r.kernel.org>
> Cc: Andreas Gruenbacher <agruenba@...hat.com>
> Fixes: 764a5c6b1fa4 ("xattr handlers: Simplify list operation")
> Signed-off-by: Richard Weinberger <richard@....at>

Reviewed-by: Andreas Gruenbacher <agruenba@...hat.com>

> ---
> Andreas,
>
> since you maintain the attr package too, I report it right here. :-)
> This jffs2 bug lead to a crash in attr_list().
>
> for() will loop to crash when there is no trailing \0 in the
> list of xattrs.
>
> for (l = lbuf; l != lbuf + length; l = strchr(l, '\0') + 1) {
>         if (api_unconvert(name, l, flags))
>                 continue;
>
> ...
> }
>
> I suggest changing the loop condition to something like l < lbuf + length.

With that change alone, strchr would still go beyond the buffer. Let's
just append a null character at the end instead.

Thanks,
Andreas

> Thanks,
> //richard
> ---
>  fs/jffs2/xattr.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/fs/jffs2/xattr.c b/fs/jffs2/xattr.c
> index da3e18503c65..0cb322eb9516 100644
> --- a/fs/jffs2/xattr.c
> +++ b/fs/jffs2/xattr.c
> @@ -967,6 +967,7 @@ ssize_t jffs2_listxattr(struct dentry *dentry, char *buffer, size_t size)
>         struct jffs2_xattr_ref *ref, **pref;
>         struct jffs2_xattr_datum *xd;
>         const struct xattr_handler *xhandle;
> +       char *orig_buffer = buffer;
>         const char *prefix;
>         ssize_t prefix_len, len, rc;
>         int retry = 0;
> @@ -977,6 +978,7 @@ ssize_t jffs2_listxattr(struct dentry *dentry, char *buffer, size_t size)
>
>         down_read(&c->xattr_sem);
>   retry:
> +       buffer = orig_buffer;
>         len = 0;
>         for (ref=ic->xref, pref=&ic->xref; ref; pref=&ref->next, ref=ref->next) {
>                 BUG_ON(ref->ic != ic);
> --
> 2.20.0
>