[PATCH 4.20 101/145] KEYS: fix parsing invalid pkey info string

[Greg Kroah-Hartman]

4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@xxxxxxxxxx>

commit 57b0e31453209d746c99e513d80b3d0c44a80891 upstream.

We need to check the return value of match_token() for Opt_err before
doing anything with it.

[ Not only did the old "-1" value for Opt_err cause problems for the
  __test_and_set_bit(), as fixed in commit 94c13f66e13c ("security:
  don't use a negative Opt_err token index"), but accessing
  "args[0].from" is invalid for the Opt_err case, as pointed out by Eric
  later.  - Linus ]

Reported-by: syzbot+a22e0dc07567662c50bc@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 00d60fd3b932 ("KEYS: Provide keyctls to drive the new key type ops for asymmetric keys [ver #2]")
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Cc: stable@xxxxxxxxxx # 4.20
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 security/keys/keyctl_pkey.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/security/keys/keyctl_pkey.c
+++ b/security/keys/keyctl_pkey.c
@@ -50,6 +50,8 @@ static int keyctl_pkey_params_parse(stru
 		if (*p == '\0' || *p == ' ' || *p == '\t')
 			continue;
 		token = match_token(p, param_keys, args);
+		if (token == Opt_err)
+			return -EINVAL;
 		if (__test_and_set_bit(token, &token_mask))
 			return -EINVAL;
 		q = args[0].from;