[PATCH net v2] net: do not leave a dangling sk pointer, when socket creation fails

[Ignat Korchagin <ignat@cloudflare.com>]

A KASAN enabled kernel will log something like below (decoded and stripped):
[   78.328507][  T299] ==================================================================
[ 78.329018][ T299] BUG: KASAN: slab-use-after-free in __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
[   78.329366][  T299] Read of size 8 at addr ffff888007110dd8 by task traceroute/299
[   78.329366][  T299]
[   78.329366][  T299] CPU: 2 PID: 299 Comm: traceroute Tainted: G            E      6.10.0-rc2+ #2
[   78.329366][  T299] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[   78.329366][  T299] Call Trace:
[   78.329366][  T299]  <TASK>
[ 78.329366][ T299] dump_stack_lvl (lib/dump_stack.c:117 (discriminator 1))
[ 78.329366][ T299] print_report (mm/kasan/report.c:378 mm/kasan/report.c:488)
[ 78.329366][ T299] ? __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
[ 78.329366][ T299] kasan_report (mm/kasan/report.c:603)
[ 78.329366][ T299] ? __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
[ 78.329366][ T299] kasan_check_range (mm/kasan/generic.c:183 mm/kasan/generic.c:189)
[ 78.329366][ T299] __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
[ 78.329366][ T299] bpf_get_socket_ptr_cookie (./arch/x86/include/asm/preempt.h:94 ./include/linux/sock_diag.h:42 net/core/filter.c:5094 net/core/filter.c:5092)
[ 78.329366][ T299] bpf_prog_875642cf11f1d139___sock_release+0x6e/0x8e
[ 78.329366][ T299] bpf_trampoline_6442506592+0x47/0xaf
[ 78.329366][ T299] __sock_release (net/socket.c:652)
[ 78.329366][ T299] __sock_create (net/socket.c:1601)
...
[   78.329366][  T299] Allocated by task 299 on cpu 2 at 78.328492s:
[ 78.329366][ T299] kasan_save_stack (mm/kasan/common.c:48)
[ 78.329366][ T299] kasan_save_track (mm/kasan/common.c:68)
[ 78.329366][ T299] __kasan_slab_alloc (mm/kasan/common.c:312 mm/kasan/common.c:338)
[ 78.329366][ T299] kmem_cache_alloc_noprof (mm/slub.c:3941 mm/slub.c:4000 mm/slub.c:4007)
[ 78.329366][ T299] sk_prot_alloc (net/core/sock.c:2075)
[ 78.329366][ T299] sk_alloc (net/core/sock.c:2134)
[ 78.329366][ T299] inet_create (net/ipv4/af_inet.c:327 net/ipv4/af_inet.c:252)
[ 78.329366][ T299] __sock_create (net/socket.c:1572)
[ 78.329366][ T299] __sys_socket (net/socket.c:1660 net/socket.c:1644 net/socket.c:1706)
[ 78.329366][ T299] __x64_sys_socket (net/socket.c:1718)
[ 78.329366][ T299] do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
[ 78.329366][ T299] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
[   78.329366][  T299]
[   78.329366][  T299] Freed by task 299 on cpu 2 at 78.328502s:
[ 78.329366][ T299] kasan_save_stack (mm/kasan/common.c:48)
[ 78.329366][ T299] kasan_save_track (mm/kasan/common.c:68)
[ 78.329366][ T299] kasan_save_free_info (mm/kasan/generic.c:582)
[ 78.329366][ T299] poison_slab_object (mm/kasan/common.c:242)
[ 78.329366][ T299] __kasan_slab_free (mm/kasan/common.c:256)
[ 78.329366][ T299] kmem_cache_free (mm/slub.c:4437 mm/slub.c:4511)
[ 78.329366][ T299] __sk_destruct (net/core/sock.c:2117 net/core/sock.c:2208)
[ 78.329366][ T299] inet_create (net/ipv4/af_inet.c:397 net/ipv4/af_inet.c:252)
[ 78.329366][ T299] __sock_create (net/socket.c:1572)
[ 78.329366][ T299] __sys_socket (net/socket.c:1660 net/socket.c:1644 net/socket.c:1706)
[ 78.329366][ T299] __x64_sys_socket (net/socket.c:1718)
[ 78.329366][ T299] do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
[ 78.329366][ T299] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)

Fix this by clearing the struct socket reference in sk_common_release() to cover
all protocol families create functions.

Fixes: c5dbb89fc2ac ("bpf: Expose bpf_get_socket_cookie to tracing programs")
Suggested-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Ignat Korchagin <ignat@cloudflare.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/netdev/20240613194047.36478-1-kuniyu@amazon.com/T/
---
Changes in v2:
  * moved the NULL-ing of the socket reference to sk_common_release() (as
    suggested by Kuniyuki Iwashima)
  * trimmed down the KASAN report in the commit message to show only relevant
    info

 net/core/sock.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/net/core/sock.c b/net/core/sock.c
index 8629f9aecf91..575af557c46b 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -3742,6 +3742,17 @@ void sk_common_release(struct sock *sk)
 
 	sk->sk_prot->unhash(sk);
 
+	/*
+	 * struct net_proto_family create functions like inet_create() or
+	 * inet6_create() have an error path, which call this function. This sk
+	 * may have already been associated with a struct socket, so ensure to
+	 * clear this reference not to leave a dangling pointer in the
+	 * struct socket instance.
+	 */
+
+	if (sk->sk_socket)
+		sk->sk_socket->sk = NULL;
+
 	/*
 	 * In this point socket cannot receive new packets, but it is possible
 	 * that some packets are in flight because some CPU runs receiver and
-- 
2.39.2