[PATCH v2] fscrypt: fix dereference of NULL user_key_payload

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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