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SubjectRe: Oops (request_key_auth_describe) while running cve-2016-7042 from LTP
Date
Can you try this patch instead of Hillf's?

David
---
commit df882ad6d4e24a3763719c1798ea58e87d56c2d7
Author: Hillf Danton <hdanton@sina.com>
Date: Fri Aug 30 15:54:33 2019 +0100

keys: Fix missing null pointer check in request_key_auth_describe()

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.

Fixes: 04c567d9313e ("[PATCH] Keys: Fix race between two instantiators of a key")
Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
Signed-off-by: David Howells <dhowells@redhat.com>

diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c
index e73ec040e250..ecba39c93fd9 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 = dereference_key_rcu(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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