[PATCH v3 03/11] cifs: Fix potential softlockups while refreshing DFS cache

Paulo Alcantara (SUSE)
2019-11-27T00:37:15Z

We used to skip reconnects on all SMB2_IOCTL commands due to SMB3+
FSCTL_VALIDATE_NEGOTIATE_INFO - which made sense since we're still
establishing a SMB session.

However, when refresh_cache_worker() calls smb2_get_dfs_refer() and
we're under reconnect, SMB2_ioctl() will not be able to get a proper
status error (e.g. -EHOSTDOWN in case we failed to reconnect) but an
-EAGAIN from cifs_send_recv() thus looping forever in
refresh_cache_worker().

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Suggested-by: Aurelien Aptel <aaptel@suse.com>
Fixes: e99c63e4d86d ("SMB3: Fix deadlock in validate negotiate hits reconnect")
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
---
fs/cifs/smb2pdu.c | 41 +++++++++++++++++++++++++++++------------
1 file changed, 29 insertions(+), 12 deletions(-)

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index c09ca6963394..3cd90088d8ac 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -252,7 +252,7 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon)
if (tcon == NULL)
return 0;

- if (smb2_command == SMB2_TREE_CONNECT || smb2_command == SMB2_IOCTL)
+ if (smb2_command == SMB2_TREE_CONNECT)
return 0;

if (tcon->tidStatus == CifsExiting) {
@@ -426,16 +426,9 @@ fill_small_buf(__le16 smb2_command, struct cifs_tcon *tcon, void *buf,
* SMB information in the SMB header. If the return code is zero, this
* function must have filled in request_buf pointer.
*/
-static int
-smb2_plain_req_init(__le16 smb2_command, struct cifs_tcon *tcon,
- void **request_buf, unsigned int *total_len)
+static int __smb2_plain_req_init(__le16 smb2_command, struct cifs_tcon *tcon,
+ void **request_buf, unsigned int *total_len)
{
- int rc;
-
- rc = smb2_reconnect(smb2_command, tcon);
- if (rc)
- return rc;
-
/* BB eventually switch this to SMB2 specific small buf size */
if (smb2_command == SMB2_SET_INFO)
*request_buf = cifs_buf_get();
@@ -456,7 +449,31 @@ smb2_plain_req_init(__le16 smb2_command, struct cifs_tcon *tcon,
cifs_stats_inc(&tcon->num_smbs_sent);
}

- return rc;
+ return 0;
+}
+
+static int smb2_plain_req_init(__le16 smb2_command, struct cifs_tcon *tcon,
+ void **request_buf, unsigned int *total_len)
+{
+ int rc;
+
+ rc = smb2_reconnect(smb2_command, tcon);
+ if (rc)
+ return rc;
+
+ return __smb2_plain_req_init(smb2_command, tcon, request_buf,
+ total_len);
+}
+
+static int smb2_ioctl_req_init(u32 opcode, struct cifs_tcon *tcon,
+ void **request_buf, unsigned int *total_len)
+{
+ /* Skip reconnect only for FSCTL_VALIDATE_NEGOTIATE_INFO IOCTLs */
+ if (opcode == FSCTL_VALIDATE_NEGOTIATE_INFO) {
+ return __smb2_plain_req_init(SMB2_IOCTL, tcon, request_buf,
+ total_len);
+ }
+ return smb2_plain_req_init(SMB2_IOCTL, tcon, request_buf, total_len);
}

/* For explanation of negotiate contexts see MS-SMB2 section 2.2.3.1 */
@@ -2686,7 +2703,7 @@ SMB2_ioctl_init(struct cifs_tcon *tcon, struct smb_rqst *rqst,
int rc;
char *in_data_buf;

- rc = smb2_plain_req_init(SMB2_IOCTL, tcon, (void **) &req, &total_len);
+ rc = smb2_ioctl_req_init(opcode, tcon, (void **) &req, &total_len);
if (rc)
return rc;

--
2.24.0