From: Sujal Tuladhar Date: Sat, 1 Aug 2026 15:53:03 +0000 (+0900) Subject: ksmbd: apply the pre-authentication PDU limit when decompressing X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=ab88cb66cb0028cb8038b64c2fa71b0f3e91d5f2;p=thirdparty%2Fkernel%2Flinux.git ksmbd: apply the pre-authentication PDU limit when decompressing ksmbd_conn_handler_loop() caps a request from an unauthenticated connection at SMB3_MAX_MSGSIZE, and only allows the larger SMB3_MAX_MSGSIZE + conn->vals->max_write_size once the connection has authenticated. ksmbd_decompress_request() runs inside that same loop but applies the authenticated limit unconditionally, and then allocates from it. The unauthenticated cap is not re-applied afterwards, as the caller only refreshes pdu_size from the new RFC1002 header. An unauthenticated client that negotiates SMB 3.1.1 with a compression context can therefore send a 104 byte chained transform whose OriginalCompressedSegmentSize is SMB3_MAX_MSGSIZE + max_write_size and have ksmbd kvmalloc() that much memory, 4210693 bytes by default. The payload costs the client nothing, because a SMB3_COMPRESS_PATTERN payload expands an eight byte structure into arbitrarily many output bytes. The decompressed PDU is rejected later by ksmbd_smb2_check_message(), but that happens in the worker, after the allocation has been made and conn->req_running has been incremented, and it results in an error response rather than dropping the connection. A client that stops reading its socket keeps each work queued for up to KSMBD_TCP_SEND_TIMEOUT while ksmbd_conn_write() holds conn->srv_mutex, so the allocations accumulate up to server_conf.max_inflight_req per connection. Move the limit into ksmbd_max_allowed_pdu_size() and call it from both sites, so the authentication state is consulted in one place and the two ceilings cannot drift apart again. Fixes: a08de24c2b85 ("ksmbd: negotiate and decode SMB2 compression") Signed-off-by: Sujal Tuladhar Acked-by: Namjae Jeon Signed-off-by: Steve French --- diff --git a/fs/smb/server/compress.c b/fs/smb/server/compress.c index 7e13cae705e2..01d1771ff663 100644 --- a/fs/smb/server/compress.c +++ b/fs/smb/server/compress.c @@ -64,7 +64,7 @@ int ksmbd_decompress_request(struct ksmbd_conn *conn) return -EINVAL; } - max_allowed_pdu_size = SMB3_MAX_MSGSIZE + conn->vals->max_write_size; + max_allowed_pdu_size = ksmbd_max_allowed_pdu_size(conn); if (out_size < sizeof(struct smb2_pdu) || out_size > max_allowed_pdu_size || out_size > MAX_STREAM_PROT_LEN) diff --git a/fs/smb/server/connection.c b/fs/smb/server/connection.c index dee8e4aced99..ef6f202f4024 100644 --- a/fs/smb/server/connection.c +++ b/fs/smb/server/connection.c @@ -488,11 +488,7 @@ recheck: pdu_size = get_rfc1002_len(hdr_buf); ksmbd_debug(CONN, "RFC1002 header %u bytes\n", pdu_size); - if (ksmbd_conn_good(conn)) - max_allowed_pdu_size = - SMB3_MAX_MSGSIZE + conn->vals->max_write_size; - else - max_allowed_pdu_size = SMB3_MAX_MSGSIZE; + max_allowed_pdu_size = ksmbd_max_allowed_pdu_size(conn); if (pdu_size > max_allowed_pdu_size) { pr_err_ratelimited("PDU length(%u) exceeded maximum allowed pdu size(%u) on connection(%d)\n", diff --git a/fs/smb/server/connection.h b/fs/smb/server/connection.h index 2a194ee36fb4..0e4ebfac5558 100644 --- a/fs/smb/server/connection.h +++ b/fs/smb/server/connection.h @@ -210,6 +210,15 @@ static inline bool ksmbd_conn_good(struct ksmbd_conn *conn) return READ_ONCE(conn->status) == KSMBD_SESS_GOOD; } +static inline unsigned int +ksmbd_max_allowed_pdu_size(struct ksmbd_conn *conn) +{ + if (ksmbd_conn_good(conn)) + return SMB3_MAX_MSGSIZE + conn->vals->max_write_size; + + return SMB3_MAX_MSGSIZE; +} + static inline bool ksmbd_conn_need_negotiate(struct ksmbd_conn *conn) { return READ_ONCE(conn->status) == KSMBD_SESS_NEED_NEGOTIATE;