[PATCH] jffs2: Fix retry handling jffs2_listxattr

[PATCH] jffs2: Fix retry handling jffs2_listxattr

[Richard Weinberger]

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@vger.kernel.org>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Fixes: 764a5c6b1fa4 ("xattr handlers: Simplify list operation")
Signed-off-by: Richard Weinberger <richard@nod.at>
---
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.

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

Re: [PATCH] jffs2: Fix retry handling jffs2_listxattr

[Andreas Gruenbacher]

Hi Richard,

On Sat, 15 Dec 2018 at 11:22, Richard Weinberger <richard@nod.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@vger.kernel.org>
> Cc: Andreas Gruenbacher <agruenba@redhat.com>
> Fixes: 764a5c6b1fa4 ("xattr handlers: Simplify list operation")
> Signed-off-by: Richard Weinberger <richard@nod.at>

Reviewed-by: Andreas Gruenbacher <agruenba@redhat.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
>