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keys: Fix missing null pointer check in request_key_auth_describe()

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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: 04c567d931 ("[PATCH] Keys: Fix race between two instantiators of a key")
Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
Signed-off-by: Hillf Danton <hdanton@sina.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hillf Danton 2019-09-02 13:37:29 +01:00 committed by Linus Torvalds
parent a3f5e1f578
commit d41a3effbb
1 changed files with 6 additions and 0 deletions
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6
security/keys/request_key_auth.c
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@ -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;