From 363b02dab09b3226f3bd1420dad9c72b79a42a76 Mon Sep 17 00:00:00 2001 From: David Howells Date: Wed, 4 Oct 2017 16:43:25 +0100 Subject: KEYS: Fix race between updating and finding a negative key Consolidate KEY_FLAG_INSTANTIATED, KEY_FLAG_NEGATIVE and the rejection error into one field such that: (1) The instantiation state can be modified/read atomically. (2) The error can be accessed atomically with the state. (3) The error isn't stored unioned with the payload pointers. This deals with the problem that the state is spread over three different objects (two bits and a separate variable) and reading or updating them atomically isn't practical, given that not only can uninstantiated keys change into instantiated or rejected keys, but rejected keys can also turn into instantiated keys - and someone accessing the key might not be using any locking. The main side effect of this problem is that what was held in the payload may change, depending on the state. For instance, you might observe the key to be in the rejected state. You then read the cached error, but if the key semaphore wasn't locked, the key might've become instantiated between the two reads - and you might now have something in hand that isn't actually an error code. The state is now KEY_IS_UNINSTANTIATED, KEY_IS_POSITIVE or a negative error code if the key is negatively instantiated. The key_is_instantiated() function is replaced with key_is_positive() to avoid confusion as negative keys are also 'instantiated'. Additionally, barriering is included: (1) Order payload-set before state-set during instantiation. (2) Order state-read before payload-read when using the key. Further separate barriering is necessary if RCU is being used to access the payload content after reading the payload pointers. Fixes: 146aa8b1453b ("KEYS: Merge the type-specific data with the payload data") Cc: stable@vger.kernel.org # v4.4+ Reported-by: Eric Biggers Signed-off-by: David Howells Reviewed-by: Eric Biggers --- security/keys/trusted.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'security/keys/trusted.c') diff --git a/security/keys/trusted.c b/security/keys/trusted.c index ddfaebf60fc8..bd85315cbfeb 100644 --- a/security/keys/trusted.c +++ b/security/keys/trusted.c @@ -1066,7 +1066,7 @@ static int trusted_update(struct key *key, struct key_preparsed_payload *prep) char *datablob; int ret = 0; - if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) + if (key_is_negative(key)) return -ENOKEY; p = key->payload.data[0]; if (!p->migratable) -- cgit v1.2.3 From a3c812f7cfd80cf51e8f5b7034f7418f6beb56c1 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Thu, 2 Nov 2017 00:47:12 +0000 Subject: KEYS: trusted: fix writing past end of buffer in trusted_read() When calling keyctl_read() on a key of type "trusted", if the user-supplied buffer was too small, the kernel ignored the buffer length and just wrote past the end of the buffer, potentially corrupting userspace memory. Fix it by instead returning the size required, as per the documentation for keyctl_read(). We also don't even fill the buffer at all in this case, as this is slightly easier to implement than doing a short read, and either behavior appears to be permitted. It also makes it match the behavior of the "encrypted" key type. Fixes: d00a1c72f7f4 ("keys: add new trusted key-type") Reported-by: Ben Hutchings Cc: # v2.6.38+ Signed-off-by: Eric Biggers Signed-off-by: David Howells Reviewed-by: Mimi Zohar Reviewed-by: James Morris Signed-off-by: James Morris --- security/keys/trusted.c | 23 ++++++++++++----------- 1 file changed, 12 insertions(+), 11 deletions(-) (limited to 'security/keys/trusted.c') diff --git a/security/keys/trusted.c b/security/keys/trusted.c index bd85315cbfeb..98aa89ff7bfd 100644 --- a/security/keys/trusted.c +++ b/security/keys/trusted.c @@ -1147,20 +1147,21 @@ static long trusted_read(const struct key *key, char __user *buffer, p = dereference_key_locked(key); if (!p) return -EINVAL; - if (!buffer || buflen <= 0) - return 2 * p->blob_len; - ascii_buf = kmalloc(2 * p->blob_len, GFP_KERNEL); - if (!ascii_buf) - return -ENOMEM; - bufp = ascii_buf; - for (i = 0; i < p->blob_len; i++) - bufp = hex_byte_pack(bufp, p->blob[i]); - if ((copy_to_user(buffer, ascii_buf, 2 * p->blob_len)) != 0) { + if (buffer && buflen >= 2 * p->blob_len) { + ascii_buf = kmalloc(2 * p->blob_len, GFP_KERNEL); + if (!ascii_buf) + return -ENOMEM; + + bufp = ascii_buf; + for (i = 0; i < p->blob_len; i++) + bufp = hex_byte_pack(bufp, p->blob[i]); + if (copy_to_user(buffer, ascii_buf, 2 * p->blob_len) != 0) { + kzfree(ascii_buf); + return -EFAULT; + } kzfree(ascii_buf); - return -EFAULT; } - kzfree(ascii_buf); return 2 * p->blob_len; } -- cgit v1.2.3