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af_packet: Fix fortified memcpy() without flex array.

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Sergei Trofimovich reported a regression [0] caused by commit a0ade8404c
("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/ [1]
Fixes: a0ade8404c ("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>
This commit is contained in:
Kuniyuki Iwashima 2023-10-09 08:31:52 -07:00 committed by Paolo Abeni
parent 71c299c711
commit e2bca4870f
2 changed files with 7 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/uapi/linux/if_packet.h
View File

@ -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 */

7
net/packet/af_packet.c
View File

@ -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;