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

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Date:   Sat, 15 Dec 2018 11:13:29 +0100
From:   Richard Weinberger <richard@....at>
To:     linux-mtd@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, dwmw2@...radead.org,
        Richard Weinberger <richard@....at>, stable@...r.kernel.org,
        Andreas Gruenbacher <agruenba@...hat.com>
Subject: [PATCH] jffs2: Fix retry handling jffs2_listxattr

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>
---
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