AI Trajectory

null

{
  "EnableConfigs": [
    "IP_SCTP"
  ],
  "FocusSymbols": [
    "sctp_recvmsg",
    "sctp_skb_recv_datagram"
  ],
  "Reasoning": "The patch modifies the return value of sctp_skb_recv_datagram to return ERR_PTR instead of NULL. However, in sctp_recvmsg, it checks IS_ERR(skb) but sctp_skb_recv_datagram can still return NULL (ERR_PTR(0)) when RCV_SHUTDOWN is set, leading to a NULL pointer dereference on skb-\u003elen. This is a functional change and a bug that should be fuzzed.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 98f7b741db1d5c2ee29848af25fbcc60e414a127\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Mon Jul 20 09:02:34 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h\nindex d50c27812504f3..b86d50d6b14688 100644\n--- a/include/net/sctp/sctp.h\n+++ b/include/net/sctp/sctp.h\n@@ -97,7 +97,7 @@ void sctp_sock_rfree(struct sk_buff *skb);\n \n extern struct percpu_counter sctp_sockets_allocated;\n int sctp_asconf_mgmt(struct sctp_sock *, struct sctp_sockaddr_entry *);\n-struct sk_buff *sctp_skb_recv_datagram(struct sock *, int, int *);\n+struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags);\n \n typedef int (*sctp_callback_t)(struct sctp_endpoint *, struct sctp_transport *, void *);\n void sctp_transport_walk_start(struct rhashtable_iter *iter);\ndiff --git a/net/sctp/socket.c b/net/sctp/socket.c\nindex c7b9e325ec1cd3..2deaa498e6cf89 100644\n--- a/net/sctp/socket.c\n+++ b/net/sctp/socket.c\n@@ -2123,9 +2123,11 @@ static int sctp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,\n \t\tgoto out;\n \t}\n \n-\tskb = sctp_skb_recv_datagram(sk, flags, \u0026err);\n-\tif (!skb)\n+\tskb = sctp_skb_recv_datagram(sk, flags);\n+\tif (IS_ERR(skb)) {\n+\t\terr = PTR_ERR(skb);\n \t\tgoto out;\n+\t}\n \n \t/* Get the total length of the skb including any skb's in the\n \t * frag_list.\n@@ -9082,7 +9084,7 @@ static int sctp_wait_for_packet(struct sock *sk, int *err, long *timeo_p)\n  * Note: This is pretty much the same routine as in core/datagram.c\n  * with a few changes to make lksctp work.\n  */\n-struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags, int *err)\n+struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags)\n {\n \tint error;\n \tstruct sk_buff *skb;\n@@ -9117,21 +9119,19 @@ struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags, int *err)\n \t\tif (error)\n \t\t\tgoto no_packet;\n \n-\t\tif (sk-\u003esk_shutdown \u0026 RCV_SHUTDOWN)\n+\t\tif (sk-\u003esk_shutdown \u0026 RCV_SHUTDOWN) {\n+\t\t\terror = 0;\n \t\t\tbreak;\n-\n+\t\t}\n \n \t\t/* User doesn't want to wait.  */\n \t\terror = -EAGAIN;\n \t\tif (!timeo)\n \t\t\tgoto no_packet;\n-\t} while (sctp_wait_for_packet(sk, err, \u0026timeo) == 0);\n-\n-\treturn NULL;\n+\t} while (sctp_wait_for_packet(sk, \u0026error, \u0026timeo) == 0);\n \n no_packet:\n-\t*err = error;\n-\treturn NULL;\n+\treturn ERR_PTR(error);\n }\n \n /* If sndbuf has changed, wake up per association sndbuf waiters.  */\ndiff --git a/net/sctp/ulpevent.c b/net/sctp/ulpevent.c\nindex 8920ca92a0115c..21ae0adbaeefbc 100644\n--- a/net/sctp/ulpevent.c\n+++ b/net/sctp/ulpevent.c\n@@ -1061,10 +1061,9 @@ void sctp_ulpevent_read_nxtinfo(const struct sctp_ulpevent *event,\n \t\t\t\tstruct sock *sk)\n {\n \tstruct sk_buff *skb;\n-\tint err;\n \n-\tskb = sctp_skb_recv_datagram(sk, MSG_PEEK | MSG_DONTWAIT, \u0026err);\n-\tif (skb != NULL) {\n+\tskb = sctp_skb_recv_datagram(sk, MSG_PEEK | MSG_DONTWAIT);\n+\tif (!IS_ERR_OR_NULL(skb)) {\n \t\t__sctp_ulpevent_read_nxtinfo(sctp_skb2event(skb),\n \t\t\t\t\t     msghdr, skb);\n \t\t/* Just release refcount here. */\n"
}

gemini-3.1-pro-preview

null

{
  "EnableConfigs": [
    "IP_SCTP"
  ],
  "FocusSymbols": [
    "sctp_recvmsg",
    "sctp_skb_recv_datagram"
  ],
  "Reasoning": "The patch modifies the return value of sctp_skb_recv_datagram to return ERR_PTR instead of NULL. However, in sctp_recvmsg, it checks IS_ERR(skb) but sctp_skb_recv_datagram can still return NULL (ERR_PTR(0)) when RCV_SHUTDOWN is set, leading to a NULL pointer dereference on skb-\u003elen. This is a functional change and a bug that should be fuzzed.",
  "WorthFuzzing": true
}

You are an expert Linux kernel maintainer.
Your job is to review a provided patch series and determine
if it makes functional changes to the kernel that should be fuzzed.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on your internal knowledge of the kernel. You must actively
use your code access tools to examine the actual source code and confirm any assumptions.

Return WorthFuzzing=false if the patch only contains:
- Modifications to Documentation/, Kconfig files, or code comments.
- Purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints.
- Changes to numeric constants or macros that do not functionally alter execution flow.
- Code paths that are impossible to reach in virtualized environments like GCE or QEMU,
even when utilizing software-emulated hardware (e.g., usb gadget, mac80211_hwsim).

If it modifies reachable core kernel logic, drivers, or architectures, use your code search
tools to verify the code can be executed, then return WorthFuzzing=true.

When returning WorthFuzzing=true, you MUST ALSO:
1. Extract any specific kernel functions that should be heavily fuzzed into FocusSymbols.
   Avoid listing generic hot-path functions to prevent skewed test distributions.
2. Identify any specific CONFIG_ options required to properly test this new/modified feature.
   Go and look into the Kconfig files and check for ifdefs around the code, do not make assumptions.
   Do not list too generic configs (we already have them enabled). Only list those that
   specifically cover the modified code. List them in the EnableConfigs output array,
   and DO NOT add a 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4").
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

For your convenience, here is the diff of the changes:
commit 98f7b741db1d5c2ee29848af25fbcc60e414a127
Author: syz-cluster <triage@syzkaller.com>
Date:   Mon Jul 20 09:02:34 2026 +0000

    syz-cluster: applied patch under review

diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
index d50c27812504f3..b86d50d6b14688 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 c7b9e325ec1cd3..2deaa498e6cf89 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 8920ca92a0115c..21ae0adbaeefbc 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. */

gemini-3.1-pro-preview

null

null

							input: 2918
							output: 35
							thoughts: 975
						

**Analyzing the SCTP Socket Receive Logic Patch**

Okay, so I'm looking at this patch that's modifying the SCTP socket receive logic, specifically the `sctp_skb_recv_datagram` function. It seems they've changed the function signature from taking an error pointer to returning an `ERR_PTR(error)` instead. This affects how errors are handled, and I need to be sure the consequences are understood.

The original code in `sctp_recvmsg` and `sctp_ulpevent_read_nxtinfo` used the old signature with the error pointer. The patch replaces the error pointer with checking if the function returns an error with the `IS_ERR` macro. So the logic now checks if the return value of `sctp_skb_recv_datagram` is an error pointer.

My initial thought was, "Wait, if it's always returning an error pointer in place of NULL, then the check makes sense". But then I dug into the `sctp_skb_recv_datagram` code itself. There's a case where `sk->sk_shutdown & RCV_SHUTDOWN` is true. In this case, it sets `error = 0` and breaks, which means it will return `ERR_PTR(0)`. Now, I have to remember that `ERR_PTR(0)` **is** NULL. So, the function can actually return `NULL` in this scenario! `IS_ERR(NULL)` is false, which means that the code in `sctp_recvmsg` will proceed as though it has a valid `skb` when it doesn't.

Looking at `sctp_recvmsg`, if `skb` is `NULL`, the code will attempt to dereference it by accessing `skb->len`. This will lead to a crash! That's a critical bug! I'm going to flag this immediately. I'll need to see how `sctp_recvmsg` is supposed to handle the `NULL` return or whether it's an oversight. I'll need to check the entire `net/sctp/socket.c` file to be certain about the ramifications of this potential null pointer dereference.

{
  "Expression": "sctp_recvmsg",
  "PathPrefix": "net/sctp/socket.c"
}

{
  "Output": "net/sctp/socket.c=2056=static int sctp_skb_pull(struct sk_buff *skb, int len)\n--\nnet/sctp/socket.c-2097- */\nnet/sctp/socket.c:2098:static int sctp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,\nnet/sctp/socket.c-2099-\t\t\tint flags)\n--\nnet/sctp/socket.c=3409=static int sctp_setsockopt_context(struct sock *sk,\n--\nnet/sctp/socket.c-3456- * come from a different association (thus the user must receive data\nnet/sctp/socket.c:3457: * with the extended calls (e.g. sctp_recvmsg) to keep track of which\nnet/sctp/socket.c-3458- * association each receive belongs to.\n--\nnet/sctp/socket.c=9654=struct proto sctp_prot = {\n--\nnet/sctp/socket.c-9667-\t.sendmsg     =\tsctp_sendmsg,\nnet/sctp/socket.c:9668:\t.recvmsg     =\tsctp_recvmsg,\nnet/sctp/socket.c-9669-\t.bind        =\tsctp_bind,\n--\nnet/sctp/socket.c=9709=struct proto sctpv6_prot = {\n--\nnet/sctp/socket.c-9722-\t.sendmsg\t= sctp_sendmsg,\nnet/sctp/socket.c:9723:\t.recvmsg\t= sctp_recvmsg,\nnet/sctp/socket.c-9724-\t.bind\t\t= sctp_bind,\n"
}

gemini-3.1-pro-preview

null

null

							input: 4902
							output: 38
							thoughts: 32
						

Okay, let's dive into this. Here's how I'd approach summarizing the thought process, considering I'm an expert in this field:

**Analyzing the `sctp_recvmsg` Function**

Alright, I'm thinking we need to dissect `sctp_recvmsg`, specifically within the `net/sctp/socket.c` file, around line 2123. My immediate goal is to understand how it handles receiving SCTP messages at a fundamental level. I want to zero in on its core logic – how it pulls data from the transport, how it manages message boundaries, what error conditions it checks for, and how it delivers the data to the user space. I'll need to remember the surrounding context within the file, which usually informs the implementation choices.

{
  "File": "net/sctp/socket.c",
  "FirstLine": 2110,
  "LineCount": 50
}

{
  "Contents": "2110:\t\n2111:\t\tif (unlikely(flags \u0026 MSG_ERRQUEUE))\n2112:\t\t\treturn inet_recv_error(sk, msg, len);\n2113:\t\n2114:\t\tif (sk_can_busy_loop(sk) \u0026\u0026\n2115:\t\t    skb_queue_empty_lockless(\u0026sk-\u003esk_receive_queue))\n2116:\t\t\tsk_busy_loop(sk, flags \u0026 MSG_DONTWAIT);\n2117:\t\n2118:\t\tlock_sock(sk);\n2119:\t\n2120:\t\tif (sctp_style(sk, TCP) \u0026\u0026 !sctp_sstate(sk, ESTABLISHED) \u0026\u0026\n2121:\t\t    !sctp_sstate(sk, CLOSING) \u0026\u0026 !sctp_sstate(sk, CLOSED)) {\n2122:\t\t\terr = -ENOTCONN;\n2123:\t\t\tgoto out;\n2124:\t\t}\n2125:\t\n2126:\t\tskb = sctp_skb_recv_datagram(sk, flags);\n2127:\t\tif (IS_ERR(skb)) {\n2128:\t\t\terr = PTR_ERR(skb);\n2129:\t\t\tgoto out;\n2130:\t\t}\n2131:\t\n2132:\t\t/* Get the total length of the skb including any skb's in the\n2133:\t\t * frag_list.\n2134:\t\t */\n2135:\t\tskb_len = skb-\u003elen;\n2136:\t\n2137:\t\tcopied = skb_len;\n2138:\t\tif (copied \u003e len)\n2139:\t\t\tcopied = len;\n2140:\t\n2141:\t\terr = skb_copy_datagram_msg(skb, 0, msg, copied);\n2142:\t\n2143:\t\tevent = sctp_skb2event(skb);\n2144:\t\n2145:\t\tif (err)\n2146:\t\t\tgoto out_free;\n2147:\t\n2148:\t\tif (event-\u003echunk \u0026\u0026 event-\u003echunk-\u003ehead_skb)\n2149:\t\t\thead_skb = event-\u003echunk-\u003ehead_skb;\n2150:\t\telse\n2151:\t\t\thead_skb = skb;\n2152:\t\tsock_recv_cmsgs(msg, sk, head_skb);\n2153:\t\tif (sctp_ulpevent_is_notification(event)) {\n2154:\t\t\tmsg-\u003emsg_flags |= MSG_NOTIFICATION;\n2155:\t\t\tsp-\u003epf-\u003eevent_msgname(event, msg-\u003emsg_name, \u0026msg-\u003emsg_namelen);\n2156:\t\t} else {\n2157:\t\t\tsp-\u003epf-\u003eskb_msgname(head_skb, msg-\u003emsg_name, \u0026msg-\u003emsg_namelen);\n2158:\t\t}\n2159:\t\n"
}

gemini-3.1-pro-preview

null

null

							input: 5925
							output: 38
							thoughts: 63
						

Okay, let me think this through.

**The Null SKB Conundrum**

Wait a minute... if the `skb` pointer is actually `NULL`, then `IS_ERR(skb)` is going to evaluate to `false`. That's not good, because then the code moves on to `skb_len = skb->len;`... which is going to try and dereference a null pointer! I'm pretty sure that's a recipe for a kernel panic, or at the very least, some seriously undefined behavior. I need to be *absolutely* certain that we're handling the case of a `NULL skb` correctly. I'm going to pull up the `sctp_skb_recv_datagram` function again and re-examine the logic, line by line. Gotta make sure there's a guard against this possibility, or it's a critical bug. I can't believe I almost missed this!

{
  "File": "net/sctp/socket.c",
  "FirstLine": 9080,
  "LineCount": 50
}

{
  "Contents": "9080:\t\treturn error;\n9081:\t}\n9082:\t\n9083:\t/* Receive a datagram.\n9084:\t * Note: This is pretty much the same routine as in core/datagram.c\n9085:\t * with a few changes to make lksctp work.\n9086:\t */\n9087:\tstruct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags)\n9088:\t{\n9089:\t\tint error;\n9090:\t\tstruct sk_buff *skb;\n9091:\t\tlong timeo;\n9092:\t\n9093:\t\ttimeo = sock_rcvtimeo(sk, flags \u0026 MSG_DONTWAIT);\n9094:\t\n9095:\t\tpr_debug(\"%s: timeo:%ld, max:%ld\\n\", __func__, timeo,\n9096:\t\t\t MAX_SCHEDULE_TIMEOUT);\n9097:\t\n9098:\t\tdo {\n9099:\t\t\t/* Again only user level code calls this function,\n9100:\t\t\t * so nothing interrupt level\n9101:\t\t\t * will suddenly eat the receive_queue.\n9102:\t\t\t *\n9103:\t\t\t *  Look at current nfs client by the way...\n9104:\t\t\t *  However, this function was correct in any case. 8)\n9105:\t\t\t */\n9106:\t\t\tif (flags \u0026 MSG_PEEK) {\n9107:\t\t\t\tskb = skb_peek(\u0026sk-\u003esk_receive_queue);\n9108:\t\t\t\tif (skb)\n9109:\t\t\t\t\trefcount_inc(\u0026skb-\u003eusers);\n9110:\t\t\t} else {\n9111:\t\t\t\tskb = __skb_dequeue(\u0026sk-\u003esk_receive_queue);\n9112:\t\t\t}\n9113:\t\n9114:\t\t\tif (skb)\n9115:\t\t\t\treturn skb;\n9116:\t\n9117:\t\t\t/* Caller is allowed not to check sk-\u003esk_err before calling. */\n9118:\t\t\terror = sock_error(sk);\n9119:\t\t\tif (error)\n9120:\t\t\t\tgoto no_packet;\n9121:\t\n9122:\t\t\tif (sk-\u003esk_shutdown \u0026 RCV_SHUTDOWN) {\n9123:\t\t\t\terror = 0;\n9124:\t\t\t\tbreak;\n9125:\t\t\t}\n9126:\t\n9127:\t\t\t/* User doesn't want to wait.  */\n9128:\t\t\terror = -EAGAIN;\n9129:\t\t\tif (!timeo)\n"
}

gemini-3.1-pro-preview

null

null

							input: 6931
							output: 38
							thoughts: 74
						

Okay, let me think this through.

**Analyzing the Function's Control Flow**

Alright, so if `sk->sk_shutdown & RCV_SHUTDOWN` is true, the loop *immediately* exits. My first thought was that it would jump to `no_packet:`, but no, that's incorrect. It breaks out of the loop and the *very next* line is the `return ERR_PTR(error);` statement. That's a crucial detail. I need to keep that in mind. Okay, I'm going to have to read the rest of this function to fully understand the logic here. I can't jump to any assumptions yet.

{
  "File": "net/sctp/socket.c",
  "FirstLine": 9120,
  "LineCount": 30
}

{
  "Contents": "9120:\t\t\t\tgoto no_packet;\n9121:\t\n9122:\t\t\tif (sk-\u003esk_shutdown \u0026 RCV_SHUTDOWN) {\n9123:\t\t\t\terror = 0;\n9124:\t\t\t\tbreak;\n9125:\t\t\t}\n9126:\t\n9127:\t\t\t/* User doesn't want to wait.  */\n9128:\t\t\terror = -EAGAIN;\n9129:\t\t\tif (!timeo)\n9130:\t\t\t\tgoto no_packet;\n9131:\t\t} while (sctp_wait_for_packet(sk, \u0026error, \u0026timeo) == 0);\n9132:\t\n9133:\tno_packet:\n9134:\t\treturn ERR_PTR(error);\n9135:\t}\n9136:\t\n9137:\t/* If sndbuf has changed, wake up per association sndbuf waiters.  */\n9138:\tstatic void __sctp_write_space(struct sctp_association *asoc)\n9139:\t{\n9140:\t\tstruct sock *sk = asoc-\u003ebase.sk;\n9141:\t\n9142:\t\tif (sctp_wspace(asoc) \u003c= 0)\n9143:\t\t\treturn;\n9144:\t\n9145:\t\tif (waitqueue_active(\u0026asoc-\u003ewait))\n9146:\t\t\twake_up_interruptible(\u0026asoc-\u003ewait);\n9147:\t\n9148:\t\tif (sctp_writeable(sk)) {\n9149:\t\t\tstruct socket_wq *wq;\n"
}

gemini-3.1-pro-preview

null

null

							input: 7617
							output: 34
							thoughts: 774
						

**A Critical SCTP Bug Discovered!**

Okay, so I've been digging through this SCTP code, and I've stumbled upon something rather nasty. It looks like a recent patch introduced a potentially critical bug. Let me break it down.

First, I see this:

```c
		if (sk->sk_shutdown & RCV_SHUTDOWN) {
			error = 0;
			break;
		}
```

If `sk->sk_shutdown & RCV_SHUTDOWN` is true, indicating a shutdown on the receive side, the loop breaks, and `error` is set to 0. Now, this feeds into the `no_packet` label, which returns `ERR_PTR(error)`. In this case that's `ERR_PTR(0)`, which evaluates to `NULL`.

The problem? `sctp_skb_recv_datagram` can return `NULL`. This is fine, that's a valid return for an empty queue when shut down, or an error. However, `sctp_recvmsg` *calls* this:

```c
	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.
	 */
	skb_len = skb->len;
```

Here's the kicker: If `skb` is `NULL`, `IS_ERR(skb)` is false. That means it *skips* the error check and dereferences the `skb->len`. Boom! Null pointer dereference and a crash.

This is definitely new, it used to look like this:

```c
	skb = sctp_skb_recv_datagram(sk, flags, &err);
	if (!skb)
		goto out;
```

So previously a `NULL` would `goto out`. This is a functional change.

I double-checked `sctp_ulpevent_read_nxtinfo`, and that code *correctly* uses `!IS_ERR_OR_NULL(skb)`, which is the correct thing to do. So it correctly handles NULL.

I also checked `IS_ERR` again to make sure my understanding was correct. `IS_ERR(NULL)` is false, as expected.

So, in short: `sctp_recvmsg` *will* crash when `sctp_skb_recv_datagram` returns `NULL`. It returns `NULL` when `sk->sk_shutdown & RCV_SHUTDOWN` is set *and* the receive queue is empty. This is easily reachable. It will crash on the `skb->len` dereference.

I'd say this is definitely fuzz-worthy. It's a functional change that introduced a bug. I need to focus my fuzzing on `sctp_recvmsg` and `sctp_skb_recv_datagram`. The target config should be `IP_SCTP`.

{
  "Expression": "config IP_SCTP",
  "PathPrefix": "net/sctp/Kconfig"
}

{
  "Output": "net/sctp/Kconfig-5-\nnet/sctp/Kconfig:6:menuconfig IP_SCTP\nnet/sctp/Kconfig-7-\ttristate \"The SCTP Protocol\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 9193
							output: 31
							thoughts: 21
						

Here's my take on the thought process:

**Diving into Configuration**

Okay, so the initial config I'm working with is `IP_SCTP`. My immediate instinct is to see if this is the only one in play. I need to get a broader view of the system's configuration landscape. There could be related or overlapping settings I need to consider, or even conflicting ones. This initial configuration might be a starting point, but I need a bigger picture to really understand its implications and interactions with other components. Digging deeper is always the first step.

{
  "Expression": "config SCTP",
  "PathPrefix": "net/sctp/Kconfig"
}

{
  "Output": "net/sctp/Kconfig=39=if IP_SCTP\nnet/sctp/Kconfig-40-\nnet/sctp/Kconfig:41:config SCTP_DBG_OBJCNT\nnet/sctp/Kconfig-42-\tbool \"SCTP: Debug object counts\"\n--\nnet/sctp/Kconfig=52=choice\n--\nnet/sctp/Kconfig-61-\nnet/sctp/Kconfig:62:config SCTP_DEFAULT_COOKIE_HMAC_SHA256\nnet/sctp/Kconfig-63-\tbool \"HMAC-SHA256\"\nnet/sctp/Kconfig-64-\nnet/sctp/Kconfig:65:config SCTP_DEFAULT_COOKIE_HMAC_NONE\nnet/sctp/Kconfig-66-\tbool \"None\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 9593
							output: 167
							thoughts: 174
						

**My Analysis of this Potential Fuzzing Target**

Alright, let's break this down. The key configuration here is obviously `IP_SCTP`. It's what drives this whole thing. Now, the meat of the matter...

Essentially, there's a patch that alters the return behavior of `sctp_skb_recv_datagram`. It's now going to return `ERR_PTR` instead of `NULL`. The issue arises in `sctp_recvmsg`, where the code checks for `IS_ERR(skb)`. However, `sctp_skb_recv_datagram` *can* still return `NULL` – specifically, `ERR_PTR(0)` – under certain conditions, namely when `RCV_SHUTDOWN` is set. This leads to a classic NULL pointer dereference, specifically on `skb->len`.

Therefore, the reasoning is pretty straightforward: This is a functional change. It introduces a bug, and it is a bug that we should absolutely target for fuzzing. `WorthFuzzing` is set to true, the important symbols that need to be in focus are `sctp_recvmsg` and `sctp_skb_recv_datagram` and `EnableConfigs` are correctly set up to include "IP_SCTP".

{
  "EnableConfigs": [
    "IP_SCTP"
  ],
  "FocusSymbols": [
    "sctp_recvmsg",
    "sctp_skb_recv_datagram"
  ],
  "Reasoning": "The patch modifies the return value of sctp_skb_recv_datagram to return ERR_PTR instead of NULL. However, in sctp_recvmsg, it checks IS_ERR(skb) but sctp_skb_recv_datagram can still return NULL (ERR_PTR(0)) when RCV_SHUTDOWN is set, leading to a NULL pointer dereference on skb-\u003elen. This is a functional change and a bug that should be fuzzed.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "IP_SCTP"
  ],
  "FocusSymbols": [
    "sctp_recvmsg",
    "sctp_skb_recv_datagram"
  ],
  "Reasoning": "The patch modifies the return value of sctp_skb_recv_datagram to return ERR_PTR instead of NULL. However, in sctp_recvmsg, it checks IS_ERR(skb) but sctp_skb_recv_datagram can still return NULL (ERR_PTR(0)) when RCV_SHUTDOWN is set, leading to a NULL pointer dereference on skb-\u003elen. This is a functional change and a bug that should be fuzzed.",
  "WorthFuzzing": true
}