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cifs: avoid race conditions with parallel reconnects
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When multiple processes/channels do reconnects in parallel
we used to return success immediately
negotiate/session-setup/tree-connect, causing race conditions
between processes that enter the function in parallel.
This caused several errors related to session not found to
show up during parallel reconnects.

Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Cc: stable@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>
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Shyam Prasad N authored and Steve French committed Mar 24, 2023
1 parent fddc6cc commit bc96215
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Showing 3 changed files with 76 additions and 33 deletions.
48 changes: 36 additions & 12 deletions fs/cifs/connect.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -212,31 +212,42 @@ cifs_mark_tcp_ses_conns_for_reconnect(struct TCP_Server_Info *server,
cifs_chan_update_iface(ses, server);

spin_lock(&ses->chan_lock);
if (!mark_smb_session && cifs_chan_needs_reconnect(ses, server))
goto next_session;
if (!mark_smb_session && cifs_chan_needs_reconnect(ses, server)) {
spin_unlock(&ses->chan_lock);
continue;
}

if (mark_smb_session)
CIFS_SET_ALL_CHANS_NEED_RECONNECT(ses);
else
cifs_chan_set_need_reconnect(ses, server);

cifs_dbg(FYI, "%s: channel connect bitmap: 0x%lx\n",
__func__, ses->chans_need_reconnect);

/* If all channels need reconnect, then tcon needs reconnect */
if (!mark_smb_session && !CIFS_ALL_CHANS_NEED_RECONNECT(ses))
goto next_session;
if (!mark_smb_session && !CIFS_ALL_CHANS_NEED_RECONNECT(ses)) {
spin_unlock(&ses->chan_lock);
continue;
}
spin_unlock(&ses->chan_lock);

spin_lock(&ses->ses_lock);
ses->ses_status = SES_NEED_RECON;
spin_unlock(&ses->ses_lock);

list_for_each_entry(tcon, &ses->tcon_list, tcon_list) {
tcon->need_reconnect = true;
spin_lock(&tcon->tc_lock);
tcon->status = TID_NEED_RECON;
spin_unlock(&tcon->tc_lock);
}
if (ses->tcon_ipc) {
ses->tcon_ipc->need_reconnect = true;
spin_lock(&ses->tcon_ipc->tc_lock);
ses->tcon_ipc->status = TID_NEED_RECON;
spin_unlock(&ses->tcon_ipc->tc_lock);
}

next_session:
spin_unlock(&ses->chan_lock);
}
spin_unlock(&cifs_tcp_ses_lock);
}
Expand Down Expand Up @@ -3653,11 +3664,19 @@ cifs_negotiate_protocol(const unsigned int xid, struct cifs_ses *ses,

/* only send once per connect */
spin_lock(&server->srv_lock);
if (!server->ops->need_neg(server) ||
if (server->tcpStatus != CifsGood &&
server->tcpStatus != CifsNew &&
server->tcpStatus != CifsNeedNegotiate) {
spin_unlock(&server->srv_lock);
return -EHOSTDOWN;
}

if (!server->ops->need_neg(server) &&
server->tcpStatus == CifsGood) {
spin_unlock(&server->srv_lock);
return 0;
}

server->tcpStatus = CifsInNegotiate;
spin_unlock(&server->srv_lock);

Expand Down Expand Up @@ -3691,23 +3710,28 @@ cifs_setup_session(const unsigned int xid, struct cifs_ses *ses,
bool is_binding = false;

spin_lock(&ses->ses_lock);
cifs_dbg(FYI, "%s: channel connect bitmap: 0x%lx\n",
__func__, ses->chans_need_reconnect);

if (ses->ses_status != SES_GOOD &&
ses->ses_status != SES_NEW &&
ses->ses_status != SES_NEED_RECON) {
spin_unlock(&ses->ses_lock);
return 0;
return -EHOSTDOWN;
}

/* only send once per connect */
spin_lock(&ses->chan_lock);
if (CIFS_ALL_CHANS_GOOD(ses) ||
cifs_chan_in_reconnect(ses, server)) {
if (CIFS_ALL_CHANS_GOOD(ses)) {
if (ses->ses_status == SES_NEED_RECON)
ses->ses_status = SES_GOOD;
spin_unlock(&ses->chan_lock);
spin_unlock(&ses->ses_lock);
return 0;
}
is_binding = !CIFS_ALL_CHANS_NEED_RECONNECT(ses);

cifs_chan_set_in_reconnect(ses, server);
is_binding = !CIFS_ALL_CHANS_NEED_RECONNECT(ses);
spin_unlock(&ses->chan_lock);

if (!is_binding)
Expand Down
44 changes: 26 additions & 18 deletions fs/cifs/smb2pdu.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -203,6 +203,7 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
}
spin_unlock(&server->srv_lock);

again:
rc = cifs_wait_for_server_reconnect(server, tcon->retry);
if (rc)
return rc;
Expand All @@ -221,6 +222,7 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,

nls_codepage = load_nls_default();

mutex_lock(&ses->session_mutex);
/*
* Recheck after acquire mutex. If another thread is negotiating
* and the server never sends an answer the socket will be closed
Expand All @@ -229,6 +231,11 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
spin_lock(&server->srv_lock);
if (server->tcpStatus == CifsNeedReconnect) {
spin_unlock(&server->srv_lock);
mutex_unlock(&ses->session_mutex);

if (tcon->retry)
goto again;

rc = -EHOSTDOWN;
goto out;
}
Expand All @@ -238,19 +245,22 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
* need to prevent multiple threads trying to simultaneously
* reconnect the same SMB session
*/
spin_lock(&ses->ses_lock);
spin_lock(&ses->chan_lock);
if (!cifs_chan_needs_reconnect(ses, server)) {
if (!cifs_chan_needs_reconnect(ses, server) &&
ses->ses_status == SES_GOOD) {
spin_unlock(&ses->chan_lock);

spin_unlock(&ses->ses_lock);
/* this means that we only need to tree connect */
if (tcon->need_reconnect)
goto skip_sess_setup;

mutex_unlock(&ses->session_mutex);
goto out;
}
spin_unlock(&ses->chan_lock);
spin_unlock(&ses->ses_lock);

mutex_lock(&ses->session_mutex);
rc = cifs_negotiate_protocol(0, ses, server);
if (!rc) {
rc = cifs_setup_session(0, ses, server, nls_codepage);
Expand All @@ -266,10 +276,8 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
mutex_unlock(&ses->session_mutex);
goto out;
}
mutex_unlock(&ses->session_mutex);

skip_sess_setup:
mutex_lock(&ses->session_mutex);
if (!tcon->need_reconnect) {
mutex_unlock(&ses->session_mutex);
goto out;
Expand All @@ -284,7 +292,7 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
cifs_dbg(FYI, "reconnect tcon rc = %d\n", rc);
if (rc) {
/* If sess reconnected but tcon didn't, something strange ... */
pr_warn_once("reconnect tcon failed rc = %d\n", rc);
cifs_dbg(VFS, "reconnect tcon failed rc = %d\n", rc);
goto out;
}

Expand Down Expand Up @@ -1256,9 +1264,9 @@ SMB2_sess_alloc_buffer(struct SMB2_sess_data *sess_data)
if (rc)
return rc;

spin_lock(&ses->chan_lock);
is_binding = !CIFS_ALL_CHANS_NEED_RECONNECT(ses);
spin_unlock(&ses->chan_lock);
spin_lock(&ses->ses_lock);
is_binding = (ses->ses_status == SES_GOOD);
spin_unlock(&ses->ses_lock);

if (is_binding) {
req->hdr.SessionId = cpu_to_le64(ses->Suid);
Expand Down Expand Up @@ -1416,9 +1424,9 @@ SMB2_auth_kerberos(struct SMB2_sess_data *sess_data)
goto out_put_spnego_key;
}

spin_lock(&ses->chan_lock);
is_binding = !CIFS_ALL_CHANS_NEED_RECONNECT(ses);
spin_unlock(&ses->chan_lock);
spin_lock(&ses->ses_lock);
is_binding = (ses->ses_status == SES_GOOD);
spin_unlock(&ses->ses_lock);

/* keep session key if binding */
if (!is_binding) {
Expand Down Expand Up @@ -1542,9 +1550,9 @@ SMB2_sess_auth_rawntlmssp_negotiate(struct SMB2_sess_data *sess_data)

cifs_dbg(FYI, "rawntlmssp session setup challenge phase\n");

spin_lock(&ses->chan_lock);
is_binding = !CIFS_ALL_CHANS_NEED_RECONNECT(ses);
spin_unlock(&ses->chan_lock);
spin_lock(&ses->ses_lock);
is_binding = (ses->ses_status == SES_GOOD);
spin_unlock(&ses->ses_lock);

/* keep existing ses id and flags if binding */
if (!is_binding) {
Expand Down Expand Up @@ -1610,9 +1618,9 @@ SMB2_sess_auth_rawntlmssp_authenticate(struct SMB2_sess_data *sess_data)

rsp = (struct smb2_sess_setup_rsp *)sess_data->iov[0].iov_base;

spin_lock(&ses->chan_lock);
is_binding = !CIFS_ALL_CHANS_NEED_RECONNECT(ses);
spin_unlock(&ses->chan_lock);
spin_lock(&ses->ses_lock);
is_binding = (ses->ses_status == SES_GOOD);
spin_unlock(&ses->ses_lock);

/* keep existing ses id and flags if binding */
if (!is_binding) {
Expand Down
17 changes: 14 additions & 3 deletions fs/cifs/smb2transport.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,7 @@ int smb2_get_sign_key(__u64 ses_id, struct TCP_Server_Info *server, u8 *key)
struct cifs_ses *ses = NULL;
int i;
int rc = 0;
bool is_binding = false;

spin_lock(&cifs_tcp_ses_lock);

Expand All @@ -97,16 +98,20 @@ int smb2_get_sign_key(__u64 ses_id, struct TCP_Server_Info *server, u8 *key)
goto out;

found:
spin_lock(&ses->ses_lock);
spin_lock(&ses->chan_lock);
if (cifs_chan_needs_reconnect(ses, server) &&
!CIFS_ALL_CHANS_NEED_RECONNECT(ses)) {

is_binding = (cifs_chan_needs_reconnect(ses, server) &&
ses->ses_status == SES_GOOD);
if (is_binding) {
/*
* If we are in the process of binding a new channel
* to an existing session, use the master connection
* session key
*/
memcpy(key, ses->smb3signingkey, SMB3_SIGN_KEY_SIZE);
spin_unlock(&ses->chan_lock);
spin_unlock(&ses->ses_lock);
goto out;
}

Expand All @@ -119,10 +124,12 @@ int smb2_get_sign_key(__u64 ses_id, struct TCP_Server_Info *server, u8 *key)
if (chan->server == server) {
memcpy(key, chan->signkey, SMB3_SIGN_KEY_SIZE);
spin_unlock(&ses->chan_lock);
spin_unlock(&ses->ses_lock);
goto out;
}
}
spin_unlock(&ses->chan_lock);
spin_unlock(&ses->ses_lock);

cifs_dbg(VFS,
"%s: Could not find channel signing key for session 0x%llx\n",
Expand Down Expand Up @@ -392,11 +399,15 @@ generate_smb3signingkey(struct cifs_ses *ses,
bool is_binding = false;
int chan_index = 0;

spin_lock(&ses->ses_lock);
spin_lock(&ses->chan_lock);
is_binding = !CIFS_ALL_CHANS_NEED_RECONNECT(ses);
is_binding = (cifs_chan_needs_reconnect(ses, server) &&
ses->ses_status == SES_GOOD);

chan_index = cifs_ses_get_chan_index(ses, server);
/* TODO: introduce ref counting for channels when the can be freed */
spin_unlock(&ses->chan_lock);
spin_unlock(&ses->ses_lock);

/*
* All channels use the same encryption/decryption keys but
Expand Down

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