Commit a3c812f7 authored Nov 02, 2017 by Eric Biggers Committed by James Morris Nov 02, 2017

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: d00a1c72 ("keys: add new trusted key-type")
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Cc: <stable@vger.kernel.org> # v2.6.38+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Reviewed-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>

parent 3239b6f2

security/keys/trusted.c

+12 −11

Original line number	Diff line number	Diff line
		@@ -1147,8 +1147,8 @@ 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;

		if (buffer && buflen >= 2 * p->blob_len) {
		ascii_buf = kmalloc(2 * p->blob_len, GFP_KERNEL);
		if (!ascii_buf)
		return -ENOMEM;
		@@ -1156,11 +1156,12 @@ static long trusted_read(const struct key key, char __user buffer,
		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 (copy_to_user(buffer, ascii_buf, 2 * p->blob_len) != 0) {
		kzfree(ascii_buf);
		return -EFAULT;
		}
		kzfree(ascii_buf);
		}
		return 2 * p->blob_len;
		}

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