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* [PATCH AUTOSEL 5.2 10/12] keys: Fix missing null pointer check in request_key_auth_describe()
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@ 2019-09-09 15:40 ` Sasha Levin
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From: Sasha Levin @ 2019-09-09 15:40 UTC (permalink / raw)
  To: linux-kernel, stable
  Cc: Hillf Danton, Sachin Sant, David Howells, Linus Torvalds,
	Sasha Levin, keyrings, linux-security-module

From: Hillf Danton <>

[ Upstream commit d41a3effbb53b1bcea41e328d16a4d046a508381 ]

If a request_key authentication token key gets revoked, there's a window in
which request_key_auth_describe() can see it with a NULL payload - but it
makes no check for this and something like the following oops may occur:

	BUG: Kernel NULL pointer dereference at 0x00000038
	Faulting instruction address: 0xc0000000004ddf30
	Oops: Kernel access of bad area, sig: 11 [#1]
	NIP [...] request_key_auth_describe+0x90/0xd0
	LR [...] request_key_auth_describe+0x54/0xd0
	Call Trace:
	[...] request_key_auth_describe+0x54/0xd0 (unreliable)
	[...] proc_keys_show+0x308/0x4c0
	[...] seq_read+0x3d0/0x540
	[...] proc_reg_read+0x90/0x110
	[...] __vfs_read+0x3c/0x70
	[...] vfs_read+0xb4/0x1b0
	[...] ksys_read+0x7c/0x130
	[...] system_call+0x5c/0x70

Fix this by checking for a NULL pointer when describing such a key.

Also make the read routine check for a NULL pointer to be on the safe side.

[DH: Modified to not take already-held rcu lock and modified to also check
 in the read routine]

Fixes: 04c567d9313e ("[PATCH] Keys: Fix race between two instantiators of a key")
Reported-by: Sachin Sant <>
Signed-off-by: Hillf Danton <>
Signed-off-by: David Howells <>
Tested-by: Sachin Sant <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Sasha Levin <>
 security/keys/request_key_auth.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c
index e45b5cf3b97fd..8491becb57270 100644
--- a/security/keys/request_key_auth.c
+++ b/security/keys/request_key_auth.c
@@ -66,6 +66,9 @@ static void request_key_auth_describe(const struct key *key,
 	struct request_key_auth *rka = get_request_key_auth(key);
+	if (!rka)
+		return;
 	seq_puts(m, "key:");
 	seq_puts(m, key->description);
 	if (key_is_positive(key))
@@ -83,6 +86,9 @@ static long request_key_auth_read(const struct key *key,
 	size_t datalen;
 	long ret;
+	if (!rka)
+		return -EKEYREVOKED;
 	datalen = rka->callout_len;
 	ret = datalen;

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