[PATCH 0/3] net: lwip: fix use-after-free bugs in the wget and dns commands

[PATCH 0/3] net: lwip: fix use-after-free bugs in the wget and dns commands

[Shahriyar Jalayeri]

Three use-after-free bugs in the lwIP wget and dns command glue.

Patch 1 fixes httpc_recv_cb(), which calls altcp_abort() on a store_block()
failure but returns ERR_BUF instead of ERR_ABRT, so tcp_input() keeps using
the freed pcb.

Patch 2 fixes wget, which keeps its transfer context on the stack and hands
its address to the httpc callbacks. Ctrl-C while the host name is still
resolving leaves the connection up, and a later callback runs against the
freed stack frame, writing attacker-controlled data through store_block().
The context moves to the heap with an ownership handoff to the lwIP callback.

Patch 3 fixes the same stack-lifetime bug in the dns command, for its
dns_gethostbyname() callback argument.

A reproducer is available on request.

Signed-off-by: Shahriyar Jalayeri <shahriyar@byteray.co.uk>
---
Shahriyar Jalayeri (3):
      net: lwip: wget: return ERR_ABRT after aborting the connection
      net: lwip: wget: free the transfer context after an aborted request
      net: lwip: dns: free the callback context after an aborted lookup

 net/lwip/dns.c  | 38 ++++++++++++++++++++++------
 net/lwip/wget.c | 77 ++++++++++++++++++++++++++++++++++++++++++++-------------
 2 files changed, 91 insertions(+), 24 deletions(-)
---
base-commit: baa64b2f892890f00a377eac4a3e685472bb56b5
change-id: 20260811-lwip-httpc-uaf-31bf85307bce

Best regards,
--  
Shahriyar Jalayeri <shahriyar@byteray.co.uk>

[PATCH 1/3] net: lwip: wget: return ERR_ABRT after aborting the connection

[Shahriyar Jalayeri]

On a store_block() failure httpc_recv_cb() calls altcp_abort(), which
frees the pcb, and then returns ERR_BUF. lwIP's receive-callback contract
requires ERR_ABRT once tcp_abort() has been called. On any other return
value tcp_input() keeps using the freed pcb (for example it stores the
segment in pcb->refused_data), a use-after-free.

Return ERR_ABRT so tcp_input() stops touching the pcb.

Fixes: 3c656c928bd7 ("net: lwip: add wget command")
Signed-off-by: Shahriyar Jalayeri <shahriyar@byteray.co.uk>
---
 net/lwip/wget.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/lwip/wget.c b/net/lwip/wget.c
index 247ece18e2b..9e93765926d 100644
--- a/net/lwip/wget.c
+++ b/net/lwip/wget.c
@@ -205,8 +205,12 @@ static err_t httpc_recv_cb(void *arg, struct altcp_pcb *pcb, struct pbuf *pbuf,
 
 	for (buf = pbuf; buf; buf = buf->next) {
 		if (store_block(ctx, buf->payload, buf->len) < 0) {
+			/*
+			 * altcp_abort() freed the pcb; the recv callback must
+			 * return ERR_ABRT so tcp_input() stops using it.
+			 */
 			altcp_abort(pcb);
-			ret = ERR_BUF;
+			ret = ERR_ABRT;
 			goto out;
 		}
 	}

-- 
2.43.0

[PATCH 2/3] net: lwip: wget: free the transfer context after an aborted request

[Shahriyar Jalayeri]

wget_do_request() keeps the transfer context on the stack and passes its
address to the lwIP httpc callbacks. If the user interrupts the transfer
with Ctrl-C while the host name is still resolving, wget_handle_request()
leaves its receive loop without tearing the connection down. The pending
DNS lookup (which lwIP cannot cancel) later resolves, the connection is
established, and httpc_recv_cb() runs against a stack frame that no longer
exists. It writes attacker-controlled TCP data through store_block() to
map_sysmem(ctx->daddr), with ctx read from reused stack.

Allocate the context on the heap and add an 'abandoned' flag. On Ctrl-C
with a request still in flight, mark it abandoned and hand ownership to
the lwIP callback, which frees the context when the connection finally
tears down; the receive, headers-done and result callbacks return early
so a stale callback neither stores data nor touches wget_info.

Fixes: 3c656c928bd7 ("net: lwip: add wget command")
Signed-off-by: Shahriyar Jalayeri <shahriyar@byteray.co.uk>
---
 net/lwip/wget.c | 71 ++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 55 insertions(+), 16 deletions(-)

diff --git a/net/lwip/wget.c b/net/lwip/wget.c
index 9e93765926d..b81509dff3f 100644
--- a/net/lwip/wget.c
+++ b/net/lwip/wget.c
@@ -12,6 +12,7 @@
 #include <lwip/errno.h>
 #include <lwip/timeouts.h>
 #include <rng.h>
+#include <malloc.h>
 #include <mapmem.h>
 #include <net.h>
 #include <time.h>
@@ -39,6 +40,7 @@ struct wget_ctx {
 	ulong content_len;
 	ulong hash_count;
 	enum done_state done;
+	bool abandoned;
 };
 
 static void wget_lwip_fill_info(struct pbuf *hdr, u16_t hdr_len, u32_t hdr_cont_len)
@@ -200,6 +202,13 @@ static err_t httpc_recv_cb(void *arg, struct altcp_pcb *pcb, struct pbuf *pbuf,
 	if (!pbuf)
 		return ERR_BUF;
 
+	/* The caller gave up on this request; drop the connection. */
+	if (ctx->abandoned) {
+		altcp_abort(pcb);
+		pbuf_free(pbuf);
+		return ERR_ABRT;
+	}
+
 	if (!ctx->start_time)
 		ctx->start_time = get_timer(0);
 
@@ -227,6 +236,12 @@ static void httpc_result_cb(void *arg, httpc_result_t httpc_result,
 	struct wget_ctx *ctx = arg;
 	ulong elapsed;
 
+	/* Last callback for an abandoned request: reclaim ctx and stop. */
+	if (ctx->abandoned) {
+		free(ctx);
+		return;
+	}
+
 	wget_info->status_code = (u32)srv_res;
 
 	if (err == ERR_BUF) {
@@ -282,6 +297,9 @@ static err_t httpc_headers_done_cb(httpc_state_t *connection, void *arg, struct
 {
 	struct wget_ctx *ctx = arg;
 
+	if (ctx->abandoned)
+		return ERR_BUF;
+
 	wget_lwip_fill_info(hdr, hdr_len, content_len);
 
 	if (wget_info->check_buffer_size && (ulong)content_len > wget_info->buffer_size)
@@ -376,8 +394,17 @@ static int wget_handle_request(struct wget_ctx *ctx, bool is_https,
 
 	while (!ctx->done) {
 		net_lwip_rx(udev, netif);
-		if (ctrlc())
+		if (ctrlc()) {
+			/*
+			 * A request may still be in flight (e.g. the name is
+			 * still resolving). Hand ctx to the lwIP callback, which
+			 * frees it once the connection tears down, instead of
+			 * freeing it here under a live callback.
+			 */
+			if (!ctx->done)
+				ctx->abandoned = true;
 			break;
+		}
 	}
 
 	if (ctx->done == SUCCESS)
@@ -392,27 +419,26 @@ static int wget_handle_request(struct wget_ctx *ctx, bool is_https,
 int wget_do_request(ulong dst_addr, char *uri)
 {
 	struct udevice *udev;
-	struct wget_ctx ctx;
+	struct wget_ctx *ctx;
 	struct netif *netif;
-	bool is_https;
+	bool is_https, abandoned;
 	int ret;
 
-	ctx.daddr = dst_addr;
-	ctx.saved_daddr = dst_addr;
-	ctx.done = NOT_DONE;
-	ctx.size = 0;
-	ctx.prevsize = 0;
-	ctx.start_time = 0;
-	ctx.content_len = 0;
-	ctx.hash_count = 0;
+	ctx = calloc(1, sizeof(*ctx));
+	if (!ctx)
+		return -ENOMEM;
+
+	ctx->daddr = dst_addr;
+	ctx->saved_daddr = dst_addr;
+	ctx->done = NOT_DONE;
 
-	ret = parse_url(uri, ctx.server_name, &ctx.port, &ctx.path, &is_https);
+	ret = parse_url(uri, ctx->server_name, &ctx->port, &ctx->path, &is_https);
 	if (ret)
-		return ret;
+		goto out;
 
 	ret = net_lwip_eth_start();
 	if (ret)
-		return ret;
+		goto out;
 
 	if (!wget_info)
 		wget_info = &default_wget_info;
@@ -422,14 +448,27 @@ int wget_do_request(ulong dst_addr, char *uri)
 	netif = net_lwip_new_netif(udev);
 	if (!netif) {
 		net_lwip_eth_stop();
-		return -ENODEV;
+		ret = -ENODEV;
+		goto out;
 	}
 
-	ret = wget_handle_request(&ctx, is_https, udev, netif);
+	ret = wget_handle_request(ctx, is_https, udev, netif);
+
+	/*
+	 * If the request was abandoned the lwIP callback still owns ctx and
+	 * frees it when the connection tears down; do not free it here.
+	 */
+	abandoned = ctx->abandoned;
 
 	net_lwip_remove_netif(netif);
 	net_lwip_eth_stop();
 
+	if (!abandoned)
+		free(ctx);
+
+	return ret;
+out:
+	free(ctx);
 	return ret;
 }
 

-- 
2.43.0

[PATCH 3/3] net: lwip: dns: free the callback context after an aborted lookup

[Shahriyar Jalayeri]

do_dns() keeps its dns_cb_arg on the stack and registers its address as
the dns_gethostbyname() callback argument. lwIP has no way to cancel a
pending lookup, so if the command is interrupted or times out while the
name is still resolving, dns_cb() fires later and writes the result into
the stack frame that has since been reused.

Allocate dns_cb_arg on the heap and add an 'abandoned' flag. If the
lookup did not complete, hand ownership to dns_cb(), which frees the
context when it eventually fires; otherwise free it before returning.

Fixes: aedcfec9ed78 ("net: lwip: add dns command")
Signed-off-by: Shahriyar Jalayeri <shahriyar@byteray.co.uk>
---
 net/lwip/dns.c | 38 +++++++++++++++++++++++++++++++-------
 1 file changed, 31 insertions(+), 7 deletions(-)

diff --git a/net/lwip/dns.c b/net/lwip/dns.c
index b620b0611d6..e93720963b8 100644
--- a/net/lwip/dns.c
+++ b/net/lwip/dns.c
@@ -4,6 +4,7 @@
 #include <command.h>
 #include <console.h>
 #include <env.h>
+#include <malloc.h>
 #include <lwip/dns.h>
 #include <lwip/timeouts.h>
 #include <net.h>
@@ -15,6 +16,7 @@
 struct dns_cb_arg {
 	ip_addr_t host_ipaddr;
 	bool done;
+	bool abandoned;
 };
 
 static void do_dns_tmr(void *arg)
@@ -26,6 +28,12 @@ static void dns_cb(const char *name, const ip_addr_t *ipaddr, void *arg)
 {
 	struct dns_cb_arg *dns_cb_arg = arg;
 
+	/* Late callback for an abandoned lookup: reclaim and stop. */
+	if (dns_cb_arg->abandoned) {
+		free(dns_cb_arg);
+		return;
+	}
+
 	dns_cb_arg->done = true;
 
 	if (!ipaddr)
@@ -36,7 +44,7 @@ static void dns_cb(const char *name, const ip_addr_t *ipaddr, void *arg)
 
 static int dns_loop(struct udevice *udev, const char *name, const char *var)
 {
-	struct dns_cb_arg dns_cb_arg = { };
+	struct dns_cb_arg *dns_cb_arg;
 	struct netif *netif;
 	const char *ipstr;
 	ip_addr_t ipaddr;
@@ -52,18 +60,22 @@ static int dns_loop(struct udevice *udev, const char *name, const char *var)
 		return CMD_RET_FAILURE;
 	}
 
-	dns_cb_arg.done = false;
+	dns_cb_arg = calloc(1, sizeof(*dns_cb_arg));
+	if (!dns_cb_arg) {
+		net_lwip_remove_netif(netif);
+		return CMD_RET_FAILURE;
+	}
 
-	ret = dns_gethostbyname(name, &ipaddr, dns_cb, &dns_cb_arg);
+	ret = dns_gethostbyname(name, &ipaddr, dns_cb, dns_cb_arg);
 
 	if (ret == ERR_OK) {
-		dns_cb(name, &ipaddr, &dns_cb_arg);
+		dns_cb(name, &ipaddr, dns_cb_arg);
 	} else if (ret == ERR_INPROGRESS) {
 		start = get_timer(0);
 		sys_timeout(DNS_RESEND_MS, do_dns_tmr, NULL);
 		do {
 			net_lwip_rx(udev, netif);
-			if (dns_cb_arg.done)
+			if (dns_cb_arg->done)
 				break;
 			if (ctrlc()) {
 				printf("\nAbort\n");
@@ -75,15 +87,27 @@ static int dns_loop(struct udevice *udev, const char *name, const char *var)
 
 	net_lwip_remove_netif(netif);
 
-	if (dns_cb_arg.done && !ip_addr_isany(&dns_cb_arg.host_ipaddr)) {
-		ipstr = ipaddr_ntoa(&dns_cb_arg.host_ipaddr);
+	/*
+	 * A started lookup that never completed may still be pending in lwIP
+	 * and reference dns_cb_arg. Hand ownership to dns_cb, which frees it
+	 * when it eventually fires, instead of freeing it here.
+	 */
+	if (ret == ERR_INPROGRESS && !dns_cb_arg->done) {
+		dns_cb_arg->abandoned = true;
+		return CMD_RET_FAILURE;
+	}
+
+	if (dns_cb_arg->done && !ip_addr_isany(&dns_cb_arg->host_ipaddr)) {
+		ipstr = ipaddr_ntoa(&dns_cb_arg->host_ipaddr);
 		if (var)
 			env_set(var, ipstr);
 		else
 			printf("%s\n", ipstr);
+		free(dns_cb_arg);
 		return CMD_RET_SUCCESS;
 	}
 
+	free(dns_cb_arg);
 	return CMD_RET_FAILURE;
 }
 

-- 
2.43.0

Re: [PATCH 2/3] net: lwip: wget: free the transfer context after an aborted request

[Jerome Forissier]

Hi Shahriar,

On 11/08/2026 20:48, Shahriyar Jalayeri wrote:
> wget_do_request() keeps the transfer context on the stack and passes its
> address to the lwIP httpc callbacks. If the user interrupts the transfer
> with Ctrl-C while the host name is still resolving, wget_handle_request()
> leaves its receive loop without tearing the connection down. The pending
> DNS lookup (which lwIP cannot cancel) later resolves, the connection is
> established, and httpc_recv_cb() runs against a stack frame that no longer
> exists. It writes attacker-controlled TCP data through store_block() to
> map_sysmem(ctx->daddr), with ctx read from reused stack.
> 
> Allocate the context on the heap and add an 'abandoned' flag. On Ctrl-C
> with a request still in flight, mark it abandoned and hand ownership to
> the lwIP callback, which frees the context when the connection finally
> tears down; the receive, headers-done and result callbacks return early
> so a stale callback neither stores data nor touches wget_info.
> 
> Fixes: 3c656c928bd7 ("net: lwip: add wget command")
> Signed-off-by: Shahriyar Jalayeri <shahriyar@byteray.co.uk>
> ---
>  net/lwip/wget.c | 71 ++++++++++++++++++++++++++++++++++++++++++++-------------
>  1 file changed, 55 insertions(+), 16 deletions(-)
> 
> diff --git a/net/lwip/wget.c b/net/lwip/wget.c
> index 9e93765926d..b81509dff3f 100644
> --- a/net/lwip/wget.c
> +++ b/net/lwip/wget.c
> @@ -12,6 +12,7 @@
>  #include <lwip/errno.h>
>  #include <lwip/timeouts.h>
>  #include <rng.h>
> +#include <malloc.h>
>  #include <mapmem.h>
>  #include <net.h>
>  #include <time.h>
> @@ -39,6 +40,7 @@ struct wget_ctx {
>  	ulong content_len;
>  	ulong hash_count;
>  	enum done_state done;
> +	bool abandoned;
>  };
>  
>  static void wget_lwip_fill_info(struct pbuf *hdr, u16_t hdr_len, u32_t hdr_cont_len)
> @@ -200,6 +202,13 @@ static err_t httpc_recv_cb(void *arg, struct altcp_pcb *pcb, struct pbuf *pbuf,
>  	if (!pbuf)
>  		return ERR_BUF;
>  
> +	/* The caller gave up on this request; drop the connection. */
> +	if (ctx->abandoned) {
> +		altcp_abort(pcb);
> +		pbuf_free(pbuf);
> +		return ERR_ABRT;
> +	}
> +
>  	if (!ctx->start_time)
>  		ctx->start_time = get_timer(0);
>  
> @@ -227,6 +236,12 @@ static void httpc_result_cb(void *arg, httpc_result_t httpc_result,
>  	struct wget_ctx *ctx = arg;
>  	ulong elapsed;
>  
> +	/* Last callback for an abandoned request: reclaim ctx and stop. */
> +	if (ctx->abandoned) {
> +		free(ctx);
> +		return;
> +	}
> +
>  	wget_info->status_code = (u32)srv_res;
>  
>  	if (err == ERR_BUF) {
> @@ -282,6 +297,9 @@ static err_t httpc_headers_done_cb(httpc_state_t *connection, void *arg, struct
>  {
>  	struct wget_ctx *ctx = arg;
>  
> +	if (ctx->abandoned)
> +		return ERR_BUF;
> +
>  	wget_lwip_fill_info(hdr, hdr_len, content_len);
>  
>  	if (wget_info->check_buffer_size && (ulong)content_len > wget_info->buffer_size)
> @@ -376,8 +394,17 @@ static int wget_handle_request(struct wget_ctx *ctx, bool is_https,
>  
>  	while (!ctx->done) {
>  		net_lwip_rx(udev, netif);
> -		if (ctrlc())
> +		if (ctrlc()) {
> +			/*
> +			 * A request may still be in flight (e.g. the name is
> +			 * still resolving). Hand ctx to the lwIP callback, which
> +			 * frees it once the connection tears down, instead of
> +			 * freeing it here under a live callback.
> +			 */
> +			if (!ctx->done)
> +				ctx->abandoned = true;

One more object seems to have the same lifetime issue here: httpc_connection_t conn is
stack-allocated in wget_handle_request(), but httpc_get_file_dns() keeps a pointer to it
in the HTTP client state and later dereferences it for the headers/result callbacks.

So if Ctrl-C makes wget_handle_request() return while DNS/connect is still pending, ctx
remains valid but conn does not. Could conn be moved into struct wget_ctx (or otherwise
made to live as long as the request) as well?

>  			break;
> +		}
>  	}
>  
>  	if (ctx->done == SUCCESS)
> @@ -392,27 +419,26 @@ static int wget_handle_request(struct wget_ctx *ctx, bool is_https,
>  int wget_do_request(ulong dst_addr, char *uri)
>  {
>  	struct udevice *udev;
> -	struct wget_ctx ctx;
> +	struct wget_ctx *ctx;
>  	struct netif *netif;
> -	bool is_https;
> +	bool is_https, abandoned;
>  	int ret;
>  
> -	ctx.daddr = dst_addr;
> -	ctx.saved_daddr = dst_addr;
> -	ctx.done = NOT_DONE;
> -	ctx.size = 0;
> -	ctx.prevsize = 0;
> -	ctx.start_time = 0;
> -	ctx.content_len = 0;
> -	ctx.hash_count = 0;
> +	ctx = calloc(1, sizeof(*ctx));
> +	if (!ctx)
> +		return -ENOMEM;
> +
> +	ctx->daddr = dst_addr;
> +	ctx->saved_daddr = dst_addr;
> +	ctx->done = NOT_DONE;
>  
> -	ret = parse_url(uri, ctx.server_name, &ctx.port, &ctx.path, &is_https);
> +	ret = parse_url(uri, ctx->server_name, &ctx->port, &ctx->path, &is_https);
>  	if (ret)
> -		return ret;
> +		goto out;
>  
>  	ret = net_lwip_eth_start();
>  	if (ret)
> -		return ret;
> +		goto out;
>  
>  	if (!wget_info)
>  		wget_info = &default_wget_info;
> @@ -422,14 +448,27 @@ int wget_do_request(ulong dst_addr, char *uri)
>  	netif = net_lwip_new_netif(udev);
>  	if (!netif) {
>  		net_lwip_eth_stop();
> -		return -ENODEV;
> +		ret = -ENODEV;
> +		goto out;
>  	}
>  
> -	ret = wget_handle_request(&ctx, is_https, udev, netif);
> +	ret = wget_handle_request(ctx, is_https, udev, netif);
> +
> +	/*
> +	 * If the request was abandoned the lwIP callback still owns ctx and
> +	 * frees it when the connection tears down; do not free it here.
> +	 */
> +	abandoned = ctx->abandoned;
>  
>  	net_lwip_remove_netif(netif);
>  	net_lwip_eth_stop();
>  
> +	if (!abandoned)
> +		free(ctx);
> +
> +	return ret;
> +out:
> +	free(ctx);
>  	return ret;
>  }
Thanks,
-- 
Jerome