af_packet: Fix fortified memcpy() without flex array.

Sergei Trofimovich reported a regression [0] caused by commit a0ade8404c3b
("af_packet: Fix warning of fortified memcpy() in packet_getname().").

It introduced a flex array sll_addr_flex in struct sockaddr_ll as a
union-ed member with sll_addr to work around the fortified memcpy() check.

However, a userspace program uses a struct that has struct sockaddr_ll in
the middle, where a flex array is illegal to exist.

  include/linux/if_packet.h:24:17: error: flexible array member 'sockaddr_ll::<unnamed union>::<unnamed struct>::sll_addr_flex' not at end of 'struct packet_info_t'
     24 |                 __DECLARE_FLEX_ARRAY(unsigned char, sll_addr_flex);
        |                 ^~~~~~~~~~~~~~~~~~~~

To fix the regression, let's go back to the first attempt [1] telling
memcpy() the actual size of the array.

Reported-by: Sergei Trofimovich <slyich@gmail.com>
Closes: https://github.com/NixOS/nixpkgs/pull/252587#issuecomment-1741733002 [0]
Link: https://lore.kernel.org/netdev/20230720004410.87588-3-kuniyu@amazon.com/
Fixes: a0ade8404c3b ("af_packet: Fix warning of fortified memcpy() in packet_getname().")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20231009153151.75688-1-kuniyu@amazon.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/include/uapi/linux/if_packet.h b/include/uapi/linux/if_packet.h
index 4d0ad22..9efc423 100644 (file)
--- a/include/uapi/linux/if_packet.h
+++ b/include/uapi/linux/if_packet.h
@@ -18,11 +18,7 @@ struct sockaddr_ll {
        unsigned short  sll_hatype;
        unsigned char   sll_pkttype;
        unsigned char   sll_halen;
-       union {
-               unsigned char   sll_addr[8];
-               /* Actual length is in sll_halen. */
-               __DECLARE_FLEX_ARRAY(unsigned char, sll_addr_flex);
-       };
+       unsigned char   sll_addr[8];
 };
 
 /* Packet types */

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 8f97648..a84e00b 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3607,7 +3607,12 @@ static int packet_getname(struct socket *sock, struct sockaddr *uaddr,
        if (dev) {
                sll->sll_hatype = dev->type;
                sll->sll_halen = dev->addr_len;
-               memcpy(sll->sll_addr_flex, dev->dev_addr, dev->addr_len);
+
+               /* Let __fortify_memcpy_chk() know the actual buffer size. */
+               memcpy(((struct sockaddr_storage *)sll)->__data +
+                      offsetof(struct sockaddr_ll, sll_addr) -
+                      offsetofend(struct sockaddr_ll, sll_family),
+                      dev->dev_addr, dev->addr_len);
        } else {
                sll->sll_hatype = 0;    /* Bad: we have no ARPHRD_UNSPEC */
                sll->sll_halen = 0;