4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Biggers ebiggers@google.com
commit a3c812f7cfd80cf51e8f5b7034f7418f6beb56c1 upstream.
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 ben@decadent.org.uk 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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- security/keys/trusted.c | 23 ++++++++++++----------- 1 file changed, 12 insertions(+), 11 deletions(-)
--- a/security/keys/trusted.c +++ b/security/keys/trusted.c @@ -1147,20 +1147,21 @@ static long trusted_read(const struct ke p = rcu_dereference_key(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; }