3.16.7-ckt24 -stable review patch. If anyone has any objections, please let me
know.
---8<------------------------------------------------------------
From: Rabin Vincent <rabin.vinc...@axis.com>
commit 820962dc700598ffe8cd21b967e30e7520c34748 upstream.
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.vinc...@axis.com>
Acked-by: Shirish Pargaonkar <shirishpargaon...@gmail.com>
Signed-off-by: Steve French <sfrench@localhost.localdomain>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriq...@canonical.com>
---
fs/cifs/connect.c | 2 +-
fs/cifs/transport.c | 6 ++++--
2 files changed, 5 insertions(+), 3 deletions(-)
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 20d75b8ddb26..3a4fc1bcde43 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -354,7 +354,6 @@ cifs_reconnect(struct TCP_Server_Info *server)
server->session_key.response = NULL;
server->session_key.len = 0;
server->lstrp = jiffies;
- mutex_unlock(&server->srv_mutex);
/* mark submitted MIDs for retry and issue callback */
INIT_LIST_HEAD(&retry_list);
@@ -367,6 +366,7 @@ cifs_reconnect(struct TCP_Server_Info *server)
list_move(&mid_entry->qhead, &retry_list);
}
spin_unlock(&GlobalMid_Lock);
+ mutex_unlock(&server->srv_mutex);
cifs_dbg(FYI, "%s: issuing mid callbacks\n", __func__);
list_for_each_safe(tmp, tmp2, &retry_list) {
diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
index 18cd5650a5fc..f3e4e3b72df2 100644
--- a/fs/cifs/transport.c
+++ b/fs/cifs/transport.c
@@ -564,14 +564,16 @@ cifs_call_async(struct TCP_Server_Info *server, struct
smb_rqst *rqst,
cifs_in_send_dec(server);
cifs_save_when_sent(mid);
- if (rc < 0)
+ if (rc < 0) {
server->sequence_number -= 2;
+ cifs_delete_mid(mid);
+ }
+
mutex_unlock(&server->srv_mutex);
if (rc == 0)
return 0;
- cifs_delete_mid(mid);
add_credits(server, 1, optype);
wake_up(&server->request_q);
return rc;
