From bc2acd699938b98ea7f903d67acce4a84d6b7fe8 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Thu, 2 Nov 2017 00:47:12 +0000 Subject: [PATCH] KEYS: trusted: fix writing past end of buffer in trusted_read() 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 Signed-off-by: Eric Biggers Signed-off-by: David Howells Reviewed-by: Mimi Zohar Reviewed-by: James Morris Signed-off-by: James Morris Signed-off-by: Ben Hutchings --- security/keys/trusted.c | 23 ++++++++++++----------- 1 file changed, 12 insertions(+), 11 deletions(-) diff --git a/security/keys/trusted.c b/security/keys/trusted.c index de3ec30c084f..c73462b5b867 100644 --- a/security/keys/trusted.c +++ b/security/keys/trusted.c @@ -1089,20 +1089,21 @@ static long trusted_read(const struct key *key, char __user *buffer, 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; } -- 2.39.5