From e3835731e169a48a2c73018d135b5c08c39ea61d Mon Sep 17 00:00:00 2001 From: Wang Zhaolong Date: Mon, 11 Aug 2025 22:07:37 +0800 Subject: [PATCH] smb: client: fix mid_q_entry memleak leak with per-mid locking This is step 4/4 of a patch series to fix mid_q_entry memory leaks caused by race conditions in callback execution. In compound_send_recv(), when wait_for_response() is interrupted by signals, the code attempts to cancel pending requests by changing their callbacks to cifs_cancelled_callback. However, there's a race condition between signal interruption and network response processing that causes both mid_q_entry and server buffer leaks: ``` User foreground process cifsd cifs_readdir open_cached_dir cifs_send_recv compound_send_recv smb2_setup_request smb2_mid_entry_alloc smb2_get_mid_entry smb2_mid_entry_alloc mempool_alloc // alloc mid kref_init(&temp->refcount); // refcount = 1 mid[0]->callback = cifs_compound_callback; mid[1]->callback = cifs_compound_last_callback; smb_send_rqst rc = wait_for_response wait_event_state TASK_KILLABLE cifs_demultiplex_thread allocate_buffers server->bigbuf = cifs_buf_get() standard_receive3 ->find_mid() smb2_find_mid __smb2_find_mid kref_get(&mid->refcount) // +1 cifs_handle_standard handle_mid /* bigbuf will also leak */ mid->resp_buf = server->bigbuf server->bigbuf = NULL; dequeue_mid /* in for loop */ mids[0]->callback cifs_compound_callback /* Signal interrupts wait: rc = -ERESTARTSYS */ /* if (... || midQ[i]->mid_state == MID_RESPONSE_RECEIVED) *? midQ[0]->callback = cifs_cancelled_callback; cancelled_mid[i] = true; /* The change comes too late */ mid->mid_state = MID_RESPONSE_READY release_mid // -1 /* cancelled_mid[i] == true causes mid won't be released in compound_send_recv cleanup */ /* cifs_cancelled_callback won't executed to release mid */ ``` The root cause is that there's a race between callback assignment and execution. Fix this by introducing per-mid locking: - Add spinlock_t mid_lock to struct mid_q_entry - Add mid_execute_callback() for atomic callback execution - Use mid_lock in cancellation paths to ensure atomicity This ensures that either the original callback or the cancellation callback executes atomically, preventing reference count leaks when requests are interrupted by signals. Link: https://bugzilla.kernel.org/show_bug.cgi?id=220404 Fixes: ee258d79159a ("CIFS: Move credit processing to mid callbacks for SMB3") Signed-off-by: Wang Zhaolong Signed-off-by: Steve French --- fs/smb/client/cifsglob.h | 21 +++++++++++++++++++++ fs/smb/client/cifstransport.c | 19 +++++++++---------- fs/smb/client/connect.c | 8 ++++---- fs/smb/client/smb2ops.c | 4 ++-- fs/smb/client/smb2transport.c | 1 + fs/smb/client/transport.c | 7 +++---- 6 files changed, 40 insertions(+), 20 deletions(-) diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h index e6830ab3a546..1e64a4fb6af0 100644 --- a/fs/smb/client/cifsglob.h +++ b/fs/smb/client/cifsglob.h @@ -1732,6 +1732,7 @@ struct mid_q_entry { int mid_rc; /* rc for MID_RC */ __le16 command; /* smb command code */ unsigned int optype; /* operation type */ + spinlock_t mid_lock; bool wait_cancelled:1; /* Cancelled while waiting for response */ bool deleted_from_q:1; /* Whether Mid has been dequeued frem pending_mid_q */ bool large_buf:1; /* if valid response, is pointer to large buf */ @@ -2036,6 +2037,9 @@ require use of the stronger protocol */ * cifsFileInfo->file_info_lock cifsFileInfo->count cifs_new_fileinfo * ->invalidHandle initiate_cifs_search * ->oplock_break_cancelled + * mid_q_entry->mid_lock mid_q_entry->callback alloc_mid + * smb2_mid_entry_alloc + * (Any fields of mid_q_entry that will need protection) ****************************************************************************/ #ifdef DECLARE_GLOBALS_HERE @@ -2375,6 +2379,23 @@ static inline bool cifs_netbios_name(const char *name, size_t namelen) return ret; } +/* + * Execute mid callback atomically - ensures callback runs exactly once + * and prevents sleeping in atomic context. + */ +static inline void mid_execute_callback(struct mid_q_entry *mid) +{ + void (*callback)(struct mid_q_entry *mid); + + spin_lock(&mid->mid_lock); + callback = mid->callback; + mid->callback = NULL; /* Mark as executed, */ + spin_unlock(&mid->mid_lock); + + if (callback) + callback(mid); +} + #define CIFS_REPARSE_SUPPORT(tcon) \ ((tcon)->posix_extensions || \ (le32_to_cpu((tcon)->fsAttrInfo.Attributes) & \ diff --git a/fs/smb/client/cifstransport.c b/fs/smb/client/cifstransport.c index 352dafb888dd..e98b95eff8c9 100644 --- a/fs/smb/client/cifstransport.c +++ b/fs/smb/client/cifstransport.c @@ -46,6 +46,7 @@ alloc_mid(const struct smb_hdr *smb_buffer, struct TCP_Server_Info *server) temp = mempool_alloc(cifs_mid_poolp, GFP_NOFS); memset(temp, 0, sizeof(struct mid_q_entry)); kref_init(&temp->refcount); + spin_lock_init(&temp->mid_lock); temp->mid = get_mid(smb_buffer); temp->pid = current->pid; temp->command = cpu_to_le16(smb_buffer->Command); @@ -345,16 +346,15 @@ SendReceive(const unsigned int xid, struct cifs_ses *ses, rc = wait_for_response(server, midQ); if (rc != 0) { send_cancel(server, &rqst, midQ); - spin_lock(&server->mid_queue_lock); - if (midQ->mid_state == MID_REQUEST_SUBMITTED || - midQ->mid_state == MID_RESPONSE_RECEIVED) { + spin_lock(&midQ->mid_lock); + if (midQ->callback) { /* no longer considered to be "in-flight" */ midQ->callback = release_mid; - spin_unlock(&server->mid_queue_lock); + spin_unlock(&midQ->mid_lock); add_credits(server, &credits, 0); return rc; } - spin_unlock(&server->mid_queue_lock); + spin_unlock(&midQ->mid_lock); } rc = cifs_sync_mid_result(midQ, server); @@ -527,15 +527,14 @@ SendReceiveBlockingLock(const unsigned int xid, struct cifs_tcon *tcon, rc = wait_for_response(server, midQ); if (rc) { send_cancel(server, &rqst, midQ); - spin_lock(&server->mid_queue_lock); - if (midQ->mid_state == MID_REQUEST_SUBMITTED || - midQ->mid_state == MID_RESPONSE_RECEIVED) { + spin_lock(&midQ->mid_lock); + if (midQ->callback) { /* no longer considered to be "in-flight" */ midQ->callback = release_mid; - spin_unlock(&server->mid_queue_lock); + spin_unlock(&midQ->mid_lock); return rc; } - spin_unlock(&server->mid_queue_lock); + spin_unlock(&midQ->mid_lock); } /* We got the response - restart system call. */ diff --git a/fs/smb/client/connect.c b/fs/smb/client/connect.c index 587845a2452d..281ccbeea719 100644 --- a/fs/smb/client/connect.c +++ b/fs/smb/client/connect.c @@ -335,7 +335,7 @@ cifs_abort_connection(struct TCP_Server_Info *server) cifs_dbg(FYI, "%s: issuing mid callbacks\n", __func__); list_for_each_entry_safe(mid, nmid, &retry_list, qhead) { list_del_init(&mid->qhead); - mid->callback(mid); + mid_execute_callback(mid); release_mid(mid); } @@ -919,7 +919,7 @@ is_smb_response(struct TCP_Server_Info *server, unsigned char type) list_del_init(&mid->qhead); mid->mid_rc = mid_rc; mid->mid_state = MID_RC; - mid->callback(mid); + mid_execute_callback(mid); release_mid(mid); } @@ -1117,7 +1117,7 @@ clean_demultiplex_info(struct TCP_Server_Info *server) mid_entry = list_entry(tmp, struct mid_q_entry, qhead); cifs_dbg(FYI, "Callback mid %llu\n", mid_entry->mid); list_del_init(&mid_entry->qhead); - mid_entry->callback(mid_entry); + mid_execute_callback(mid_entry); release_mid(mid_entry); } /* 1/8th of sec is more than enough time for them to exit */ @@ -1394,7 +1394,7 @@ next_pdu: } if (!mids[i]->multiRsp || mids[i]->multiEnd) - mids[i]->callback(mids[i]); + mid_execute_callback(mids[i]); release_mid(mids[i]); } else if (server->ops->is_oplock_break && diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c index 218b6ce7ff3a..3b251de874ec 100644 --- a/fs/smb/client/smb2ops.c +++ b/fs/smb/client/smb2ops.c @@ -4814,7 +4814,7 @@ static void smb2_decrypt_offload(struct work_struct *work) dw->server->ops->is_network_name_deleted(dw->buf, dw->server); - mid->callback(mid); + mid_execute_callback(mid); } else { spin_lock(&dw->server->srv_lock); if (dw->server->tcpStatus == CifsNeedReconnect) { @@ -4822,7 +4822,7 @@ static void smb2_decrypt_offload(struct work_struct *work) mid->mid_state = MID_RETRY_NEEDED; spin_unlock(&dw->server->mid_queue_lock); spin_unlock(&dw->server->srv_lock); - mid->callback(mid); + mid_execute_callback(mid); } else { spin_lock(&dw->server->mid_queue_lock); mid->mid_state = MID_REQUEST_SUBMITTED; diff --git a/fs/smb/client/smb2transport.c b/fs/smb/client/smb2transport.c index ff9ef7fcd010..bc0e92eb2b64 100644 --- a/fs/smb/client/smb2transport.c +++ b/fs/smb/client/smb2transport.c @@ -771,6 +771,7 @@ smb2_mid_entry_alloc(const struct smb2_hdr *shdr, temp = mempool_alloc(cifs_mid_poolp, GFP_NOFS); memset(temp, 0, sizeof(struct mid_q_entry)); kref_init(&temp->refcount); + spin_lock_init(&temp->mid_lock); temp->mid = le64_to_cpu(shdr->MessageId); temp->credits = credits > 0 ? credits : 1; temp->pid = current->pid; diff --git a/fs/smb/client/transport.c b/fs/smb/client/transport.c index 32d528b4dd83..a61ba7f3fb86 100644 --- a/fs/smb/client/transport.c +++ b/fs/smb/client/transport.c @@ -1005,15 +1005,14 @@ compound_send_recv(const unsigned int xid, struct cifs_ses *ses, cifs_server_dbg(FYI, "Cancelling wait for mid %llu cmd: %d\n", midQ[i]->mid, le16_to_cpu(midQ[i]->command)); send_cancel(server, &rqst[i], midQ[i]); - spin_lock(&server->mid_queue_lock); + spin_lock(&midQ[i]->mid_lock); midQ[i]->wait_cancelled = true; - if (midQ[i]->mid_state == MID_REQUEST_SUBMITTED || - midQ[i]->mid_state == MID_RESPONSE_RECEIVED) { + if (midQ[i]->callback) { midQ[i]->callback = cifs_cancelled_callback; cancelled_mid[i] = true; credits[i].value = 0; } - spin_unlock(&server->mid_queue_lock); + spin_unlock(&midQ[i]->mid_lock); } } -- 2.25.1