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cifs: fix race between call_async() and reconnect()

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[ Upstream commit 820962dc70 ]

cifs_call_async() queues the MID to the pending list and calls
smb_send_rqst().  If smb_send_rqst() performs a partial send, it sets
the tcpStatus to CifsNeedReconnect and returns an error code to
cifs_call_async().  In this case, cifs_call_async() removes the MID
from the list and returns to the caller.

However, cifs_call_async() releases the server mutex _before_ removing
the MID.  This means that a cifs_reconnect() can race with this function
and manage to remove the MID from the list and delete the entry before
cifs_call_async() calls cifs_delete_mid().  This leads to various
crashes due to the use after free in cifs_delete_mid().

Task1				Task2

cifs_call_async():
 - rc = -EAGAIN
 - mutex_unlock(srv_mutex)

				cifs_reconnect():
				 - mutex_lock(srv_mutex)
				 - mutex_unlock(srv_mutex)
				 - list_delete(mid)
				 - mid->callback()
				 	cifs_writev_callback():
				 		- mutex_lock(srv_mutex)
						- delete(mid)
				 		- mutex_unlock(srv_mutex)

 - cifs_delete_mid(mid) <---- use after free

Fix this by removing the MID in cifs_call_async() before releasing the
srv_mutex.  Also hold the srv_mutex in cifs_reconnect() until the MIDs
are moved out of the pending list.

Signed-off-by: Rabin Vincent <rabin.vincent@axis.com>
Acked-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
CC: Stable <stable@vger.kernel.org>
Signed-off-by: Steve French <sfrench@localhost.localdomain>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
This commit is contained in:
Rabin Vincent
2015-12-23 07:32:41 +01:00
committed by Sasha Levin
parent ca7342a8a3
commit 99b79b15df
2 changed files with 5 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
fs/cifs/connect.c
View File

@@ -357,7 +357,6 @@ cifs_reconnect(struct TCP_Server_Info *server)
server->session_key.response = NULL; server->session_key.response = NULL;
server->session_key.len = 0; server->session_key.len = 0;
server->lstrp = jiffies; server->lstrp = jiffies;
mutex_unlock(&server->srv_mutex);
/* mark submitted MIDs for retry and issue callback */ /* mark submitted MIDs for retry and issue callback */
INIT_LIST_HEAD(&retry_list); INIT_LIST_HEAD(&retry_list);
@@ -370,6 +369,7 @@ cifs_reconnect(struct TCP_Server_Info *server)
list_move(&mid_entry->qhead, &retry_list); list_move(&mid_entry->qhead, &retry_list);
} }
spin_unlock(&GlobalMid_Lock); spin_unlock(&GlobalMid_Lock);
mutex_unlock(&server->srv_mutex);
cifs_dbg(FYI, "%s: issuing mid callbacks\n", __func__); cifs_dbg(FYI, "%s: issuing mid callbacks\n", __func__);
list_for_each_safe(tmp, tmp2, &retry_list) { list_for_each_safe(tmp, tmp2, &retry_list) {

6
fs/cifs/transport.c
View File

@@ -576,14 +576,16 @@ cifs_call_async(struct TCP_Server_Info *server, struct smb_rqst *rqst,
cifs_in_send_dec(server); cifs_in_send_dec(server);
cifs_save_when_sent(mid); cifs_save_when_sent(mid);
if (rc < 0) if (rc < 0) {
server->sequence_number -= 2; server->sequence_number -= 2;
cifs_delete_mid(mid);
}
mutex_unlock(&server->srv_mutex); mutex_unlock(&server->srv_mutex);
if (rc == 0) if (rc == 0)
return 0; return 0;
cifs_delete_mid(mid);
add_credits_and_wake_if(server, credits, optype); add_credits_and_wake_if(server, credits, optype);
return rc; return rc;
} }