Re: [BUG] ksmbd: OOB read in share_config_request() when payload_sz == 0

[Namjae Jeon]

On Fri, Aug 28, 2026 at 7:38 AM Farhad Alemi <farhad.alemi@xxxxxxxxxxxx> wrote:
>
> Hello Namjae and Steve,
>
> While fuzzing Linux 7.1-rc5 with syzkaller, as part of research at ASU's
> SEFCOM lab, we hit the crash below. Crash reports can be found here:
>
>   https://github.com/farhad-alemi/public_bug_reports/tree/main/106-ksmbd-oob-read-share_config_request/
>
>   BUG: KASAN: slab-out-of-bounds in strnlen+0x66/0x90 lib/string.c:432
>   kstrndup+0x2d/0x160 mm/util.c:120
>   share_config_request fs/smb/server/mgmt/share_config.c:168 [inline]
>   ksmbd_share_config_get+0x5e0/0x1190
>        fs/smb/server/mgmt/share_config.c:243
>   smb2_tree_connect+0x2f4/0x1320 fs/smb/server/smb2pdu.c:2015
>
> Our reproducer.c is available upon request.
>
> Happy to test a patch if that would help.
Can you test if the attached patch fixes this issue?

Thanks.
From d2c0970ab706b1d9e6c7960aeb17521acbc7b32c Mon Sep 17 00:00:00 2001
From: Namjae Jeon <linkinjeon@xxxxxxxxxx>
Date: Fri, 28 Aug 2026 08:39:57 +0900
Subject: [PATCH 1/2] ksmbd: prevent out-of-bounds reads in share config
 responses

Validate IPC share configuration payload sizes before consuming
variable-length fields. Bound veto list parsing and account for
the separator byte when deriving the path length.

Fixes: a677ebd8ca2f ("ksmbd: validate payload size in ipc response")
Signed-off-by: Namjae Jeon <linkinjeon@xxxxxxxxxx>
---
 fs/smb/server/mgmt/share_config.c | 40 +++++++++++++++++++++----------
 fs/smb/server/transport_ipc.c     | 21 ++++++++++------
 2 files changed, 41 insertions(+), 20 deletions(-)

diff --git a/fs/smb/server/mgmt/share_config.c b/fs/smb/server/mgmt/share_config.c
index b2d9580bddc6..cc9f18ede80d 100644
--- a/fs/smb/server/mgmt/share_config.c
+++ b/fs/smb/server/mgmt/share_config.c
@@ -146,9 +146,9 @@ static struct ksmbd_share_config *__share_lookup(const char *name)
 
 static int parse_veto_list(struct ksmbd_share_config *share,
 			   char *veto_list,
-			   int veto_list_sz)
+			   size_t veto_list_sz)
 {
-	int sz = 0;
+	size_t sz;
 
 	if (!veto_list_sz)
 		return 0;
@@ -156,7 +156,7 @@ static int parse_veto_list(struct ksmbd_share_config *share,
 	while (veto_list_sz > 0) {
 		struct ksmbd_veto_pattern *p;
 
-		sz = strlen(veto_list);
+		sz = strnlen(veto_list, veto_list_sz);
 		if (!sz)
 			break;
 
@@ -164,7 +164,7 @@ static int parse_veto_list(struct ksmbd_share_config *share,
 		if (!p)
 			return -ENOMEM;
 
-		p->pattern = kstrdup(veto_list, KSMBD_DEFAULT_GFP);
+		p->pattern = kstrndup(veto_list, sz, KSMBD_DEFAULT_GFP);
 		if (!p->pattern) {
 			kfree(p);
 			return -ENOMEM;
@@ -172,6 +172,9 @@ static int parse_veto_list(struct ksmbd_share_config *share,
 
 		list_add(&p->list, &share->veto_list);
 
+		if (sz == veto_list_sz)
+			break;
+
 		veto_list += sz + 1;
 		veto_list_sz -= (sz + 1);
 	}
@@ -224,17 +227,28 @@ static struct ksmbd_share_config *share_config_request(struct ksmbd_work *work,
 	}
 
 	if (!test_share_config_flag(share, KSMBD_SHARE_FLAG_PIPE)) {
-		int path_len = PATH_MAX;
-
-		if (resp->payload_sz)
-			path_len = resp->payload_sz - resp->veto_list_sz;
+		size_t path_len;
 
-		share->path = kstrndup(ksmbd_share_config_path(resp), path_len,
-				      KSMBD_DEFAULT_GFP);
-		if (!share->path) {
-			ret = -ENOMEM;
+		if (resp->payload_sz <= resp->veto_list_sz) {
+			ret = -EINVAL;
 		} else {
-			ret = 0;
+			path_len = resp->payload_sz - resp->veto_list_sz;
+			if (resp->veto_list_sz)
+				path_len--;
+
+			if (!path_len) {
+				ret = -EINVAL;
+			} else {
+				share->path = kstrndup(
+					ksmbd_share_config_path(resp),
+					path_len, KSMBD_DEFAULT_GFP);
+				if (!share->path)
+					ret = -ENOMEM;
+				else
+					ret = 0;
+			}
+		}
+		if (share->path) {
 			share->path_sz = strlen(share->path);
 			while (share->path_sz > 1 &&
 			       share->path[share->path_sz - 1] == '/')
diff --git a/fs/smb/server/transport_ipc.c b/fs/smb/server/transport_ipc.c
index 4b0b572a3e1b..e550aa41ad2c 100644
--- a/fs/smb/server/transport_ipc.c
+++ b/fs/smb/server/transport_ipc.c
@@ -532,14 +532,21 @@ static int ipc_validate_msg(struct ipc_msg_table_entry *entry)
 		if (entry->msg_sz < sizeof(struct ksmbd_share_config_response))
 			return -EINVAL;
 
-		if (resp->payload_sz) {
-			if (resp->payload_sz < resp->veto_list_sz)
-				return -EINVAL;
+		if (strnlen(resp->share_name, sizeof(resp->share_name)) ==
+		    sizeof(resp->share_name))
+			return -EINVAL;
 
-			if (check_add_overflow(sizeof(struct ksmbd_share_config_response),
-					       resp->payload_sz, &msg_sz))
-				return -EINVAL;
-		}
+		if (resp->veto_list_sz > resp->payload_sz)
+			return -EINVAL;
+
+		if (resp->flags != KSMBD_SHARE_FLAG_INVALID &&
+		    !(resp->flags & KSMBD_SHARE_FLAG_PIPE) &&
+		    resp->payload_sz <= resp->veto_list_sz)
+			return -EINVAL;
+
+		if (check_add_overflow(sizeof(struct ksmbd_share_config_response),
+				       resp->payload_sz, &msg_sz))
+			return -EINVAL;
 		break;
 	}
 	case KSMBD_EVENT_LOGIN_REQUEST_EXT:
-- 
2.34.1