include/net/sctp/sctp.h | 2 +- net/sctp/socket.c | 20 ++++++++++---------- net/sctp/ulpevent.c | 5 ++--- 3 files changed, 13 insertions(+), 14 deletions(-)
From: Qing Luo <luoqing@kylinos.cn>
The err output parameter in sctp_skb_recv_datagram() is passed to
callers but never validated, making error reporting unreliable.
Remove it and use ERR_PTR to encode errors directly in the return
value, which is the standard kernel pattern for this case.
Signed-off-by: Qing Luo <luoqing@kylinos.cn>
---
include/net/sctp/sctp.h | 2 +-
net/sctp/socket.c | 20 ++++++++++----------
net/sctp/ulpevent.c | 5 ++---
3 files changed, 13 insertions(+), 14 deletions(-)
diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
index d50c27812504..b86d50d6b146 100644
--- a/include/net/sctp/sctp.h
+++ b/include/net/sctp/sctp.h
@@ -97,7 +97,7 @@ void sctp_sock_rfree(struct sk_buff *skb);
extern struct percpu_counter sctp_sockets_allocated;
int sctp_asconf_mgmt(struct sctp_sock *, struct sctp_sockaddr_entry *);
-struct sk_buff *sctp_skb_recv_datagram(struct sock *, int, int *);
+struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags);
typedef int (*sctp_callback_t)(struct sctp_endpoint *, struct sctp_transport *, void *);
void sctp_transport_walk_start(struct rhashtable_iter *iter);
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index c7b9e325ec1c..2deaa498e6cf 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -2123,9 +2123,11 @@ static int sctp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
goto out;
}
- skb = sctp_skb_recv_datagram(sk, flags, &err);
- if (!skb)
+ skb = sctp_skb_recv_datagram(sk, flags);
+ if (IS_ERR(skb)) {
+ err = PTR_ERR(skb);
goto out;
+ }
/* Get the total length of the skb including any skb's in the
* frag_list.
@@ -9082,7 +9084,7 @@ static int sctp_wait_for_packet(struct sock *sk, int *err, long *timeo_p)
* Note: This is pretty much the same routine as in core/datagram.c
* with a few changes to make lksctp work.
*/
-struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags, int *err)
+struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags)
{
int error;
struct sk_buff *skb;
@@ -9117,21 +9119,19 @@ struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags, int *err)
if (error)
goto no_packet;
- if (sk->sk_shutdown & RCV_SHUTDOWN)
+ if (sk->sk_shutdown & RCV_SHUTDOWN) {
+ error = 0;
break;
-
+ }
/* User doesn't want to wait. */
error = -EAGAIN;
if (!timeo)
goto no_packet;
- } while (sctp_wait_for_packet(sk, err, &timeo) == 0);
-
- return NULL;
+ } while (sctp_wait_for_packet(sk, &error, &timeo) == 0);
no_packet:
- *err = error;
- return NULL;
+ return ERR_PTR(error);
}
/* If sndbuf has changed, wake up per association sndbuf waiters. */
diff --git a/net/sctp/ulpevent.c b/net/sctp/ulpevent.c
index 8920ca92a011..21ae0adbaeef 100644
--- a/net/sctp/ulpevent.c
+++ b/net/sctp/ulpevent.c
@@ -1061,10 +1061,9 @@ void sctp_ulpevent_read_nxtinfo(const struct sctp_ulpevent *event,
struct sock *sk)
{
struct sk_buff *skb;
- int err;
- skb = sctp_skb_recv_datagram(sk, MSG_PEEK | MSG_DONTWAIT, &err);
- if (skb != NULL) {
+ skb = sctp_skb_recv_datagram(sk, MSG_PEEK | MSG_DONTWAIT);
+ if (!IS_ERR_OR_NULL(skb)) {
__sctp_ulpevent_read_nxtinfo(sctp_skb2event(skb),
msghdr, skb);
/* Just release refcount here. */
--
2.25.1
>> I think it's used at [1] in sctp_recvmsg():
>>
>> skb = sctp_skb_recv_datagram(sk, flags, &err);
>> if (!skb)
>> goto out;
> Would it make more sense to ERR_PTR() etc ?
>
>
> David
Yes, you are right. The current implementation returns a negative error
code directly via err, but it would be cleaner to use ERR_PTR() to
unify the error path with other datagram receivers.
I will refactor this part in v4:
>
>
>> ...
>>
>> out:
>> release_sock(sk);
>> return err; <------ [1]syzbot ci has tested the following series [v4] sctp: socket: refactor sctp_skb_recv_datagram to use ERR_PTR https://lore.kernel.org/all/20260720082145.1072547-1-l1138897701@163.com * [PATCH net v4] sctp: socket: refactor sctp_skb_recv_datagram to use ERR_PTR and found the following issue: general protection fault in sctp_recvmsg Full report is available here: https://ci.syzbot.org/series/f979ded9-9743-486d-b911-69a904c9f4ad *** general protection fault in sctp_recvmsg tree: net URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net.git base: e13caf1c26587434f0b768193100440939c0fb91 arch: amd64 compiler: Debian clang version 22.1.6 (++20260514074242+fc4aad7b5db3-1~exp1~20260514074407.73), Debian LLD 22.1.6 config: https://ci.syzbot.org/builds/e4b39daf-f862-498e-8aeb-c22b5a168551/config syz repro: https://ci.syzbot.org/findings/1893a3b4-56e4-49d0-9865-4ff919f027b3/syz_repro Oops: general protection fault, probably for non-canonical address 0xdffffc000000000e: 0000 [#1] SMP KASAN PTI KASAN: null-ptr-deref in range [0x0000000000000070-0x0000000000000077] CPU: 0 UID: 0 PID: 5830 Comm: syz.2.19 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 RIP: 0010:sctp_recvmsg+0x28d/0xd60 net/sctp/socket.c:2135 Code: ff 72 0d e8 35 6a d6 f6 41 89 ee e9 da 06 00 00 4c 89 7c 24 08 48 8d 7d 70 48 89 f8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <0f> b6 04 08 84 c0 0f 85 2f 08 00 00 4c 63 7d 70 4d 39 fe 4d 0f 43 RSP: 0018:ffffc90003a8f838 EFLAGS: 00010202 RAX: 000000000000000e RBX: ffff888115ad1c80 RCX: dffffc0000000000 RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000070 RBP: 0000000000000000 R08: 1ffff92000751ef4 R09: 1ffff11022b5a460 R10: dffffc0000000000 R11: fffffbfff206639f R12: ffff888115ad22f0 R13: ffffc90003a8fd00 R14: 0000000000000000 R15: 0000000000000300 FS: 00007facf6b766c0(0000) GS:ffff88818dc17000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00002000000055c0 CR3: 000000010a812000 CR4: 00000000000006f0 Call Trace: <TASK> sock_recvmsg_nosec net/socket.c:1128 [inline] sock_recvmsg+0x166/0x1e0 net/socket.c:1148 ____sys_recvmsg+0x1e6/0x4a0 net/socket.c:2904 ___sys_recvmsg+0x213/0x5a0 net/socket.c:2946 do_recvmmsg+0x31a/0x7f0 net/socket.c:3041 __sys_recvmmsg net/socket.c:3115 [inline] __do_sys_recvmmsg net/socket.c:3138 [inline] __se_sys_recvmmsg net/socket.c:3131 [inline] __x64_sys_recvmmsg+0x198/0x250 net/socket.c:3131 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7facf5d9ce59 Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007facf6b76028 EFLAGS: 00000246 ORIG_RAX: 000000000000012b RAX: ffffffffffffffda RBX: 00007facf6015fa0 RCX: 00007facf5d9ce59 RDX: 000000000400023c RSI: 00002000000055c0 RDI: 0000000000000004 RBP: 00007facf5e32e6f R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000300 R11: 0000000000000246 R12: 0000000000000000 R13: 00007facf6016038 R14: 00007facf6015fa0 R15: 00007ffcc05d60d8 </TASK> Modules linked in: ---[ end trace 0000000000000000 ]--- RIP: 0010:sctp_recvmsg+0x28d/0xd60 net/sctp/socket.c:2135 Code: ff 72 0d e8 35 6a d6 f6 41 89 ee e9 da 06 00 00 4c 89 7c 24 08 48 8d 7d 70 48 89 f8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <0f> b6 04 08 84 c0 0f 85 2f 08 00 00 4c 63 7d 70 4d 39 fe 4d 0f 43 RSP: 0018:ffffc90003a8f838 EFLAGS: 00010202 RAX: 000000000000000e RBX: ffff888115ad1c80 RCX: dffffc0000000000 RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000070 RBP: 0000000000000000 R08: 1ffff92000751ef4 R09: 1ffff11022b5a460 R10: dffffc0000000000 R11: fffffbfff206639f R12: ffff888115ad22f0 R13: ffffc90003a8fd00 R14: 0000000000000000 R15: 0000000000000300 FS: 00007facf6b766c0(0000) GS:ffff88818dc17000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00002000000055c0 CR3: 000000010a812000 CR4: 00000000000006f0 ---------------- Code disassembly (best guess): 0: ff 72 0d push 0xd(%rdx) 3: e8 35 6a d6 f6 call 0xf6d66a3d 8: 41 89 ee mov %ebp,%r14d b: e9 da 06 00 00 jmp 0x6ea 10: 4c 89 7c 24 08 mov %r15,0x8(%rsp) 15: 48 8d 7d 70 lea 0x70(%rbp),%rdi 19: 48 89 f8 mov %rdi,%rax 1c: 48 c1 e8 03 shr $0x3,%rax 20: 48 b9 00 00 00 00 00 movabs $0xdffffc0000000000,%rcx 27: fc ff df * 2a: 0f b6 04 08 movzbl (%rax,%rcx,1),%eax <-- trapping instruction 2e: 84 c0 test %al,%al 30: 0f 85 2f 08 00 00 jne 0x865 36: 4c 63 7d 70 movslq 0x70(%rbp),%r15 3a: 4d 39 fe cmp %r15,%r14 3d: 4d rex.WRB 3e: 0f .byte 0xf 3f: 43 rex.XB *** If these findings have caused you to resend the series or submit a separate fix, please add the following tag to your commit message: Tested-by: syzbot@syzkaller.appspotmail.com --- This report is generated by a bot. 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