[PATCH] unicode: add s_encoding null ptr check in utf8ncursor

[Edward AD]

When init struct utf8cursor *u8c in utf8ncursor(), we need check um is
valid.

Reported-and-tested-by: syzbot+9cf75dc581fb4307d6dd@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: b81427939590 ("ext4: remove redundant checks of s_encoding")
Signed-off-by: Edward AD <twuufnxlz@xxxxxxxxx>
---
 fs/unicode/utf8-norm.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/unicode/utf8-norm.c b/fs/unicode/utf8-norm.c
index 768f8ab448b8..906b639b2f38 100644
--- a/fs/unicode/utf8-norm.c
+++ b/fs/unicode/utf8-norm.c
@@ -422,6 +422,10 @@ int utf8ncursor(struct utf8cursor *u8c, const struct unicode_map *um,
 {
 	if (!s)
 		return -1;
+
+	if (IS_ERR_OR_NULL(um))
+		return -1;
+
 	u8c->um = um;
 	u8c->n = n;
 	u8c->s = s;
-- 
2.25.1