[PATCH 3.10 021/268] CIFS: Fix a possible memory corruption during reconnect

Willy Tarreau
2017-06-19T19:27:51Z

From: Pavel Shilovsky <pshilov@microsoft.com>

commit 53e0e11efe9289535b060a51d4cf37c25e0d0f2b upstream.

We can not unlock/lock cifs_tcp_ses_lock while walking through ses
and tcon lists because it can corrupt list iterator pointers and
a tcon structure can be released if we don't hold an extra reference.
Fix it by moving a reconnect process to a separate delayed work
and acquiring a reference to every tcon that needs to be reconnected.
Also do not send an echo request on newly established connections.

Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
fs/cifs/cifsglob.h | 3 +++
fs/cifs/cifsproto.h | 3 +++
fs/cifs/connect.c | 34 +++++++++++++++++++-----
fs/cifs/smb2pdu.c | 75 ++++++++++++++++++++++++++++++++++++-----------------
fs/cifs/smb2proto.h | 1 +
5 files changed, 85 insertions(+), 31 deletions(-)

diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index f74dfa8..28708bb 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -576,6 +576,8 @@ struct TCP_Server_Info {
#ifdef CONFIG_CIFS_SMB2
unsigned int max_read;
unsigned int max_write;
+ struct delayed_work reconnect; /* reconnect workqueue job */
+ struct mutex reconnect_mutex; /* prevent simultaneous reconnects */
#endif /* CONFIG_CIFS_SMB2 */
};

@@ -750,6 +752,7 @@ cap_unix(struct cifs_ses *ses)
struct cifs_tcon {
struct list_head tcon_list;
int tc_count;
+ struct list_head rlist; /* reconnect list */
struct list_head openFileList;
struct cifs_ses *ses; /* pointer to session associated with */
char treeName[MAX_TREE_SIZE + 1]; /* UNC name of resource in ASCII */
diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h
index dda188a..1194a8b 100644
--- a/fs/cifs/cifsproto.h
+++ b/fs/cifs/cifsproto.h
@@ -194,6 +194,9 @@ extern void cifs_add_pending_open_locked(struct cifs_fid *fid,
struct tcon_link *tlink,
struct cifs_pending_open *open);
extern void cifs_del_pending_open(struct cifs_pending_open *open);
+extern void cifs_put_tcp_session(struct TCP_Server_Info *server,
+ int from_reconnect);
+extern void cifs_put_tcon(struct cifs_tcon *tcon);

#if IS_ENABLED(CONFIG_CIFS_DFS_UPCALL)
extern void cifs_dfs_release_automount_timer(void);
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 7c33afd..0808b08 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -52,6 +52,9 @@
#include "nterr.h"
#include "rfc1002pdu.h"
#include "fscache.h"
+#ifdef CONFIG_CIFS_SMB2
+#include "smb2proto.h"
+#endif

#define CIFS_PORT 445
#define RFC1001_PORT 139
@@ -2070,8 +2073,8 @@ cifs_find_tcp_session(struct smb_vol *vol)
return NULL;
}

-static void
-cifs_put_tcp_session(struct TCP_Server_Info *server)
+void
+cifs_put_tcp_session(struct TCP_Server_Info *server, int from_reconnect)
{
struct task_struct *task;

@@ -2088,6 +2091,19 @@ cifs_put_tcp_session(struct TCP_Server_Info *server)

cancel_delayed_work_sync(&server->echo);

+#ifdef CONFIG_CIFS_SMB2
+ if (from_reconnect)
+ /*
+ * Avoid deadlock here: reconnect work calls
+ * cifs_put_tcp_session() at its end. Need to be sure
+ * that reconnect work does nothing with server pointer after
+ * that step.
+ */
+ cancel_delayed_work(&server->reconnect);
+ else
+ cancel_delayed_work_sync(&server->reconnect);
+#endif
+
spin_lock(&GlobalMid_Lock);
server->tcpStatus = CifsExiting;
spin_unlock(&GlobalMid_Lock);
@@ -2158,6 +2174,10 @@ cifs_get_tcp_session(struct smb_vol *volume_info)
INIT_LIST_HEAD(&tcp_ses->tcp_ses_list);
INIT_LIST_HEAD(&tcp_ses->smb_ses_list);
INIT_DELAYED_WORK(&tcp_ses->echo, cifs_echo_request);
+#ifdef CONFIG_CIFS_SMB2
+ INIT_DELAYED_WORK(&tcp_ses->reconnect, smb2_reconnect_server);
+ mutex_init(&tcp_ses->reconnect_mutex);
+#endif
memcpy(&tcp_ses->srcaddr, &volume_info->srcaddr,
sizeof(tcp_ses->srcaddr));
memcpy(&tcp_ses->dstaddr, &volume_info->dstaddr,
@@ -2288,7 +2308,7 @@ cifs_put_smb_ses(struct cifs_ses *ses)
_free_xid(xid);
}
sesInfoFree(ses);
- cifs_put_tcp_session(server);
+ cifs_put_tcp_session(server, 0);
}

#ifdef CONFIG_KEYS
@@ -2461,7 +2481,7 @@ cifs_get_smb_ses(struct TCP_Server_Info *server, struct smb_vol *volume_info)
mutex_unlock(&ses->session_mutex);

/* existing SMB ses has a server reference already */
- cifs_put_tcp_session(server);
+ cifs_put_tcp_session(server, 0);
free_xid(xid);
return ses;
}
@@ -2550,7 +2570,7 @@ cifs_find_tcon(struct cifs_ses *ses, const char *unc)
return NULL;
}

-static void
+void
cifs_put_tcon(struct cifs_tcon *tcon)
{
unsigned int xid;
@@ -3599,7 +3619,7 @@ mount_fail_check:
else if (ses)
cifs_put_smb_ses(ses);
else
- cifs_put_tcp_session(server);
+ cifs_put_tcp_session(server, 0);
bdi_destroy(&cifs_sb->bdi);
}

@@ -3932,7 +3952,7 @@ cifs_construct_tcon(struct cifs_sb_info *cifs_sb, kuid_t fsuid)
ses = cifs_get_smb_ses(master_tcon->ses->server, vol_info);
if (IS_ERR(ses)) {
tcon = (struct cifs_tcon *)ses;
- cifs_put_tcp_session(master_tcon->ses->server);
+ cifs_put_tcp_session(master_tcon->ses->server, 0);
goto out;
}

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 9dd8c96..133067c 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -1239,6 +1239,54 @@ smb2_echo_callback(struct mid_q_entry *mid)
add_credits(server, credits_received, CIFS_ECHO_OP);
}

+void smb2_reconnect_server(struct work_struct *work)
+{
+ struct TCP_Server_Info *server = container_of(work,
+ struct TCP_Server_Info, reconnect.work);
+ struct cifs_ses *ses;
+ struct cifs_tcon *tcon, *tcon2;
+ struct list_head tmp_list;
+ int tcon_exist = false;
+
+ /* Prevent simultaneous reconnects that can corrupt tcon->rlist list */
+ mutex_lock(&server->reconnect_mutex);
+
+ INIT_LIST_HEAD(&tmp_list);
+ cifs_dbg(FYI, "Need negotiate, reconnecting tcons\n");
+
+ spin_lock(&cifs_tcp_ses_lock);
+ list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list) {
+ list_for_each_entry(tcon, &ses->tcon_list, tcon_list) {
+ if (tcon->need_reconnect) {
+ tcon->tc_count++;
+ list_add_tail(&tcon->rlist, &tmp_list);
+ tcon_exist = true;
+ }
+ }
+ }
+ /*
+ * Get the reference to server struct to be sure that the last call of
+ * cifs_put_tcon() in the loop below won't release the server pointer.
+ */
+ if (tcon_exist)
+ server->srv_count++;
+
+ spin_unlock(&cifs_tcp_ses_lock);
+
+ list_for_each_entry_safe(tcon, tcon2, &tmp_list, rlist) {
+ smb2_reconnect(SMB2_ECHO, tcon);
+ list_del_init(&tcon->rlist);
+ cifs_put_tcon(tcon);
+ }
+
+ cifs_dbg(FYI, "Reconnecting tcons finished\n");
+ mutex_unlock(&server->reconnect_mutex);
+
+ /* now we can safely release srv struct */
+ if (tcon_exist)
+ cifs_put_tcp_session(server, 1);
+}
+
int
SMB2_echo(struct TCP_Server_Info *server)
{
@@ -1251,32 +1299,11 @@ SMB2_echo(struct TCP_Server_Info *server)
cifs_dbg(FYI, "In echo request\n");

if (server->tcpStatus == CifsNeedNegotiate) {
- struct list_head *tmp, *tmp2;
- struct cifs_ses *ses;
- struct cifs_tcon *tcon;
-
- cifs_dbg(FYI, "Need negotiate, reconnecting tcons\n");
- spin_lock(&cifs_tcp_ses_lock);
- list_for_each(tmp, &server->smb_ses_list) {
- ses = list_entry(tmp, struct cifs_ses, smb_ses_list);
- list_for_each(tmp2, &ses->tcon_list) {
- tcon = list_entry(tmp2, struct cifs_tcon,
- tcon_list);
- /* add check for persistent handle reconnect */
- if (tcon && tcon->need_reconnect) {
- spin_unlock(&cifs_tcp_ses_lock);
- rc = smb2_reconnect(SMB2_ECHO, tcon);
- spin_lock(&cifs_tcp_ses_lock);
- }
- }
- }
- spin_unlock(&cifs_tcp_ses_lock);
+ /* No need to send echo on newly established connections */
+ queue_delayed_work(cifsiod_wq, &server->reconnect, 0);
+ return rc;
}

- /* if no session, renegotiate failed above */
- if (server->tcpStatus == CifsNeedNegotiate)
- return -EIO;
-
rc = small_smb2_init(SMB2_ECHO, NULL, (void **)&req);
if (rc)
return rc;
diff --git a/fs/cifs/smb2proto.h b/fs/cifs/smb2proto.h
index 2aa3535..d0cd166 100644
--- a/fs/cifs/smb2proto.h
+++ b/fs/cifs/smb2proto.h
@@ -93,6 +93,7 @@ extern void smb2_set_oplock_level(struct cifsInodeInfo *cinode, __u32 oplock);
extern int smb2_unlock_range(struct cifsFileInfo *cfile,
struct file_lock *flock, const unsigned int xid);
extern int smb2_push_mandatory_locks(struct cifsFileInfo *cfile);
+extern void smb2_reconnect_server(struct work_struct *work);

/*
* SMB2 Worker functions - most of protocol specific implementation details
--
2.8.0.rc2.1.gbe9624a