From ad0057fb91218914d6c98268718ceb9d59b388e1 Mon Sep 17 00:00:00 2001 From: Greg Kroah-Hartman Date: Mon, 6 Apr 2026 15:46:48 +0200 Subject: [PATCH] ksmbd: fix mechToken leak when SPNEGO decode fails after token alloc The kernel ASN.1 BER decoder calls action callbacks incrementally as it walks the input. When ksmbd_decode_negTokenInit() reaches the mechToken [2] OCTET STRING element, ksmbd_neg_token_alloc() allocates conn->mechToken immediately via kmemdup_nul(). If a later element in the same blob is malformed, then the decoder will return nonzero after the allocation is already live. This could happen if mechListMIC [3] overrunse the enclosing SEQUENCE. decode_negotiation_token() then sets conn->use_spnego = false because both the negTokenInit and negTokenTarg grammars failed. The cleanup at the bottom of smb2_sess_setup() is gated on use_spnego: if (conn->use_spnego && conn->mechToken) { kfree(conn->mechToken); conn->mechToken = NULL; } so the kfree is skipped, causing the mechToken to never be freed. This codepath is reachable pre-authentication, so untrusted clients can cause slow memory leaks on a server without even being properly authenticated. Fix this up by not checking check for use_spnego, as it's not required, so the memory will always be properly freed. At the same time, always free the memory in ksmbd_conn_free() incase some other failure path forgot to free it. Cc: Namjae Jeon Cc: Steve French Cc: Sergey Senozhatsky Cc: Tom Talpey Cc: linux-cifs@vger.kernel.org Cc: Assisted-by: gregkh_clanker_t1000 Signed-off-by: Greg Kroah-Hartman Acked-by: Namjae Jeon Signed-off-by: Steve French --- fs/smb/server/connection.c | 1 + fs/smb/server/smb2pdu.c | 2 +- 2 files changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/smb/server/connection.c b/fs/smb/server/connection.c index 1bb2081c492c..26cfce344861 100644 --- a/fs/smb/server/connection.c +++ b/fs/smb/server/connection.c @@ -96,6 +96,7 @@ void ksmbd_conn_free(struct ksmbd_conn *conn) xa_destroy(&conn->sessions); kvfree(conn->request_buf); kfree(conn->preauth_info); + kfree(conn->mechToken); if (atomic_dec_and_test(&conn->refcnt)) { conn->transport->ops->free_transport(conn->transport); kfree(conn); diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c index c61fcc88d6f2..10ae77dae5a1 100644 --- a/fs/smb/server/smb2pdu.c +++ b/fs/smb/server/smb2pdu.c @@ -1915,7 +1915,7 @@ int smb2_sess_setup(struct ksmbd_work *work) else if (rc) rsp->hdr.Status = STATUS_LOGON_FAILURE; - if (conn->use_spnego && conn->mechToken) { + if (conn->mechToken) { kfree(conn->mechToken); conn->mechToken = NULL; }