[PATCH] jffs2: ensure wbuf_verify is valid before using it.

[Hou Tao]

Now MTD emulated by UBI volumn doesn't allocate wbuf_verify in
jffs2_ubivol_setup(), because UBI can do the verifcation itself,
so when CONFIG_JFFS2_FS_WBUF_VERIFY is enabled and a MTD device
emulated by UBI volumn is used, a Oops will occur as show in the
following trace:

    general protection fault: 0000 [#1] SMP KASAN PTI
    CPU: 6 PID: 404 Comm: kworker/6:1 Not tainted 4.19.0-rc8
    Workqueue: events_long delayed_wbuf_sync
    RIP: 0010:ubi_io_read+0x156/0x650
    Call Trace:
     ubi_eba_read_leb+0x57d/0xba0
     ubi_leb_read+0xe5/0x1b0
     gluebi_read+0x10c/0x1a0
     mtd_read+0x112/0x340
     jffs2_verify_write+0xef/0x440
     __jffs2_flush_wbuf+0x3fa/0x3540
     jffs2_flush_wbuf_gc+0x1b1/0x2e0
     process_one_work+0x58b/0x11e0
     worker_thread+0x8f/0xfe0
     kthread+0x2ae/0x3a0
     ret_from_fork+0x35/0x40

Fix the problem by checking the validity of wbuf_verify before
using it in jffs2_verify_write().

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 0029da3bf430 ("JFFS2: add UBI support")
Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
---
 fs/jffs2/wbuf.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/jffs2/wbuf.c b/fs/jffs2/wbuf.c
index c6821a509481..3de45f4559d1 100644
--- a/fs/jffs2/wbuf.c
+++ b/fs/jffs2/wbuf.c
@@ -234,6 +234,13 @@ static int jffs2_verify_write(struct jffs2_sb_info *c, unsigned char *buf,
 	size_t retlen;
 	char *eccstr;
 
+	/*
+	 * MTD emulated by UBI volume doesn't allocate wbuf_verify,
+	 * because it can do the verification itself.
+	 */
+	if (!c->wbuf_verify)
+		return 0;
+
 	ret = mtd_read(c->mtd, ofs, c->wbuf_pagesize, &retlen, c->wbuf_verify);
 	if (ret && ret != -EUCLEAN && ret != -EBADMSG) {
 		pr_warn("%s(): Read back of page at %08x failed: %d\n",
-- 
2.16.2.dirty