[PATCH v2] fscrypt: fix dereference of NULL user_key_payload

From: Eric Biggers <redacted>

When an fscrypt-encrypted file is opened, we request the file's master
key from the keyrings service as a logon key, then access its payload.
However, a revoked key has a NULL payload, and we failed to check for
this.  request_key() *does* skip revoked keys, but there is still a
window where the key can be revoked before we acquire its semaphore.

Fix it by checking for a NULL payload, treating it like a key which was
already revoked at the time it was requested.

Fixes: 88bd6ccdcdd6 ("ext4 crypto: add encryption key management facilities")
Reviewed-by: James Morris <redacted>
Cc: <redacted>    [v4.1+]
Signed-off-by: Eric Biggers <redacted>
---

Changed since v1: added Reviewed-by and resent as standalone patch.
Can this please be taken through the fscrypt tree?

 fs/crypto/keyinfo.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/crypto/keyinfo.c b/fs/crypto/keyinfo.c
index 018c588c7ac3..8e704d12a1cf 100644
--- a/fs/crypto/keyinfo.c
+++ b/fs/crypto/keyinfo.c

@@ -109,6 +109,11 @@ static int validate_user_key(struct fscrypt_info *crypt_info,
 		goto out;
 	}
 	ukp = user_key_payload_locked(keyring_key);
+	if (!ukp) {
+		/* key was revoked before we acquired its semaphore */
+		res = -EKEYREVOKED;
+		goto out;
+	}
 	if (ukp->datalen != sizeof(struct fscrypt_key)) {
 		res = -EINVAL;
 		goto out;

-- 
2.14.2.920.gcf0c67979c-goog

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On Mon, Oct 09, 2017 at 12:46:18PM -0700, Eric Biggers wrote:

From: Eric Biggers <redacted>

When an fscrypt-encrypted file is opened, we request the file's master
key from the keyrings service as a logon key, then access its payload.
However, a revoked key has a NULL payload, and we failed to check for
this.  request_key() *does* skip revoked keys, but there is still a
window where the key can be revoked before we acquire its semaphore.

Fix it by checking for a NULL payload, treating it like a key which was
already revoked at the time it was requested.

Fixes: 88bd6ccdcdd6 ("ext4 crypto: add encryption key management facilities")
Reviewed-by: James Morris <redacted>
Cc: <redacted>    [v4.1+]
Signed-off-by: Eric Biggers <redacted>

Applied, thanks.

					- Ted
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On Sun, Oct 29, 2017 at 06:23:05AM -0400, Theodore Ts'o wrote:

On Mon, Oct 09, 2017 at 12:46:18PM -0700, Eric Biggers wrote:

quoted

From: Eric Biggers <redacted>

When an fscrypt-encrypted file is opened, we request the file's master
key from the keyrings service as a logon key, then access its payload.
However, a revoked key has a NULL payload, and we failed to check for
this.  request_key() *does* skip revoked keys, but there is still a
window where the key can be revoked before we acquire its semaphore.

Fix it by checking for a NULL payload, treating it like a key which was
already revoked at the time it was requested.

Fixes: 88bd6ccdcdd6 ("ext4 crypto: add encryption key management facilities")
Reviewed-by: James Morris <redacted>
Cc: <redacted>    [v4.1+]
Signed-off-by: Eric Biggers <redacted>

Applied, thanks.

Hi Ted, you should drop this one, since it's already in mainline; David Howells
ended up taking the original series via the keyrings tree.

Thanks!

Eric
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On Sun, Oct 29, 2017 at 09:32:46AM -0700, Eric Biggers wrote:

Hi Ted, you should drop this one, since it's already in mainline; David Howells
ended up taking the original series via the keyrings tree.

Ah, I see it landed in v4.14-rc6.  I'll drop it from the fscrypt tree.

      	     	       		   	     - Ted
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