smc: Fix various oops due to inet_sock type confusion.

In the Linux kernel, the following vulnerability has been resolved:

smc: Fix various oops due to inet_sock type confusion.

syzbot reported weird splats [0][1] in cipso_v4_sock_setattr() while

freeing inet_sk(sk)->inet_opt.

The address was freed multiple times even though it was read-only memory.

cipso_v4_sock_setattr() did nothing wrong, and the root cause was type

confusion.

The cited commit made it possible to create smc_sock as an INET socket.

The issue is that struct smc_sock does not have struct inet_sock as the

first member but hijacks AF_INET and AF_INET6 sk_family, which confuses

various places.

In this case, inet_sock.inet_opt was actually smc_sock.clcsk_data_ready(),

which is an address of a function in the text segment.

$ pahole -C inet_sock vmlinux

struct inet_sock {

...

struct ip_options_rcu * inet_opt; /* 784 8 */

$ pahole -C smc_sock vmlinux

struct smc_sock {

...

void (*clcsk_data_ready)(struct sock *); /* 784 8 */

The same issue for another field was reported before. [2][3]

At that time, an ugly hack was suggested [4], but it makes both INET

and SMC code error-prone and hard to change.

Also, yet another variant was fixed by a hacky commit 98d4435efcbf3

("net/smc: prevent NULL pointer dereference in txopt_get").

Instead of papering over the root cause by such hacks, we should not

allow non-INET socket to reuse the INET infra.

Let's add inet_sock as the first member of smc_sock.

[0]:

kvfree_call_rcu(): Double-freed call. rcu_head 000000006921da73

WARNING: CPU: 0 PID: 6718 at mm/slab_common.c:1956 kvfree_call_rcu+0x94/0x3f0 mm/slab_common.c:1955

Modules linked in:

CPU: 0 UID: 0 PID: 6718 Comm: syz.0.17 Tainted: G W 6.16.0-rc4-syzkaller-g7482bb149b9f #0 PREEMPT

Tainted: [W]=WARN

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025

pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)

pc : kvfree_call_rcu+0x94/0x3f0 mm/slab_common.c:1955

lr : kvfree_call_rcu+0x94/0x3f0 mm/slab_common.c:1955

sp : ffff8000a03a7730

x29: ffff8000a03a7730 x28: 00000000fffffff5 x27: 1fffe000184823d3

x26: dfff800000000000 x25: ffff0000c2411e9e x24: ffff0000dd88da00

x23: ffff8000891ac9a0 x22: 00000000ffffffea x21: ffff8000891ac9a0

x20: ffff8000891ac9a0 x19: ffff80008afc2480 x18: 00000000ffffffff

x17: 0000000000000000 x16: ffff80008ae642c8 x15: ffff700011ede14c

x14: 1ffff00011ede14c x13: 0000000000000004 x12: ffffffffffffffff

x11: ffff700011ede14c x10: 0000000000ff0100 x9 : 5fa3c1ffaf0ff000

x8 : 5fa3c1ffaf0ff000 x7 : 0000000000000001 x6 : 0000000000000001

x5 : ffff8000a03a7078 x4 : ffff80008f766c20 x3 : ffff80008054d360

x2 : 0000000000000000 x1 : 0000000000000201 x0 : 0000000000000000

Call trace:

kvfree_call_rcu+0x94/0x3f0 mm/slab_common.c:1955 (P)

cipso_v4_sock_setattr+0x2f0/0x3f4 net/ipv4/cipso_ipv4.c:1914

netlbl_sock_setattr+0x240/0x334 net/netlabel/netlabel_kapi.c:1000

smack_netlbl_add+0xa8/0x158 security/smack/smack_lsm.c:2581

smack_inode_setsecurity+0x378/0x430 security/smack/smack_lsm.c:2912

security_inode_setsecurity+0x118/0x3c0 security/security.c:2706

__vfs_setxattr_noperm+0x174/0x5c4 fs/xattr.c:251

__vfs_setxattr_locked+0x1ec/0x218 fs/xattr.c:295

vfs_setxattr+0x158/0x2ac fs/xattr.c:321

do_setxattr fs/xattr.c:636 [inline]

file_setxattr+0x1b8/0x294 fs/xattr.c:646

path_setxattrat+0x2ac/0x320 fs/xattr.c:711

__do_sys_fsetxattr fs/xattr.c:761 [inline]

__se_sys_fsetxattr fs/xattr.c:758 [inline]

__arm64_sys_fsetxattr+0xc0/0xdc fs/xattr.c:758

__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]

invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49

el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132

do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151

el0_svc+0x58/0x180 arch/arm64/kernel/entry-common.c:879

el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898

el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600

[

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