Re: [PATCH] nfc: Fix the sockaddr length sanitization in llcp_sock_connect
From: Kees Cook <hidden>
Date: 2017-05-24 16:58:29
Also in:
linux-wireless, lkml
On Wed, May 24, 2017 at 3:26 AM, Mateusz Jurczyk [off-list ref] wrote:
Fix the sockaddr length verification in the connect() handler of NFC/LLCP sockets, to compare against the size of the actual structure expected on input (sockaddr_nfc_llcp) instead of its shorter version (sockaddr_nfc). Both structures are defined in include/uapi/linux/nfc.h. The fields specific to the _llcp extended struct are as follows: 276 __u8 dsap; /* Destination SAP, if known */ 277 __u8 ssap; /* Source SAP to be bound to */ 278 char service_name[NFC_LLCP_MAX_SERVICE_NAME]; /* Service name URI */; 279 size_t service_name_len; If the caller doesn't provide a sufficiently long sockaddr buffer, these fields remain uninitialized (and they currently originate from the stack frame of the top-level sys_connect handler). They are then copied by llcp_sock_connect() into internal storage (nfc_llcp_sock structure), and could be subsequently read back through the user-mode getsockname() function (handled by llcp_sock_getname()). This would result in the disclosure of up to ~70 uninitialized bytes from the kernel stack to user-mode clients capable of creating AFC_NFC sockets. Signed-off-by: Mateusz Jurczyk <redacted>
Acked-by: Kees Cook <redacted> -Kees
quoted hunk ↗ jump to hunk
--- net/nfc/llcp_sock.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)diff --git a/net/nfc/llcp_sock.c b/net/nfc/llcp_sock.c index 2ffb18e73df6..d0d12bea65cb 100644 --- a/net/nfc/llcp_sock.c +++ b/net/nfc/llcp_sock.c@@ -662,8 +662,7 @@ static int llcp_sock_connect(struct socket *sock, struct sockaddr *_addr, pr_debug("sock %p sk %p flags 0x%x\n", sock, sk, flags); - if (!addr || len < sizeof(struct sockaddr_nfc) || - addr->sa_family != AF_NFC) + if (!addr || len < sizeof(*addr) || addr->sa_family != AF_NFC) return -EINVAL; if (addr->service_name_len == 0 && addr->dsap == 0) --2.13.0.219.gdb65acc882-goog
-- Kees Cook Pixel Security