[bionic:linux-azure-4.15][PATCH 2/2] cifs: Fix potential softlockups while refreshing DFS cache

[Marcelo Henrique Cerri]

From: Paulo Alcantara (SUSE) <pc at cjr.nz>

BugLink: https://bugs.launchpad.net/bugs/1882268

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().

Fixes: e99c63e4d86d ("SMB3: Fix deadlock in validate negotiate hits reconnect")
Signed-off-by: Paulo Alcantara (SUSE) <pc at cjr.nz>
Suggested-by: Aurelien Aptel <aaptel at suse.com>
Reviewed-by: Aurelien Aptel <aaptel at suse.com>
Signed-off-by: Steve French <stfrench at microsoft.com>
(backported from commit 84a1f5b1cc6fd7f6cd99fc5630c36f631b19fa60)
[marcelo.cerri: Adapted the changes from smb2_plain_req_init() to
 small_smb2_init() to avoid picking too many unrelated changes]
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>
---
 fs/cifs/smb2pdu.c | 38 ++++++++++++++++++++++++++++----------
 1 file changed, 28 insertions(+), 10 deletions(-)

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index ec2f7c377a2b..ab1df4311a6d 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -166,7 +166,7 @@ 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) {
@@ -372,18 +372,13 @@ smb2_plain_req_init(__le16 smb2_command, struct cifs_tcon *tcon,
  * function must have filled in request_buf pointer. The returned buffer
  * has RFC1001 length at the beginning.
  */
-static int
-small_smb2_init(__le16 smb2_command, struct cifs_tcon *tcon,
-		void **request_buf)
+static int __small_smb2_init(__le16 smb2_command, struct cifs_tcon *tcon,
+			     void **request_buf)
 {
-	int rc;
+	int rc = 0;
 	unsigned int total_len;
 	struct smb2_pdu *pdu;
 
-	rc = smb2_reconnect(smb2_command, tcon);
-	if (rc)
-		return rc;
-
 	/* BB eventually switch this to SMB2 specific small buf size */
 	*request_buf = cifs_small_buf_get();
 	if (*request_buf == NULL) {
@@ -409,6 +404,29 @@ small_smb2_init(__le16 smb2_command, struct cifs_tcon *tcon,
 	return rc;
 }
 
+static int small_smb2_init(__le16 smb2_command, struct cifs_tcon *tcon,
+			   void **request_buf)
+{
+	int rc;
+
+	rc = smb2_reconnect(smb2_command, tcon);
+	if (rc)
+		return rc;
+
+	return __small_smb2_init(smb2_command, tcon, request_buf);
+}
+
+static int small_smb2_ioctl_init(u32 opcode, struct cifs_tcon *tcon,
+				 void **request_buf)
+{
+       /* Skip reconnect only for FSCTL_VALIDATE_NEGOTIATE_INFO IOCTLs */
+       if (opcode == FSCTL_VALIDATE_NEGOTIATE_INFO) {
+	       return __small_smb2_init(SMB2_IOCTL, tcon, request_buf);
+       }
+       return small_smb2_init(SMB2_IOCTL, tcon, request_buf);
+}
+
+
 #ifdef CONFIG_CIFS_SMB311
 /* offset is sizeof smb2_negotiate_req - 4 but rounded up to 8 bytes */
 #define OFFSET_OF_NEG_CONTEXT 0x68  /* sizeof(struct smb2_negotiate_req) - 4 */
@@ -1937,7 +1955,7 @@ SMB2_ioctl(const unsigned int xid, struct cifs_tcon *tcon, u64 persistent_fid,
 	if (!ses || !(ses->server))
 		return -EIO;
 
-	rc = small_smb2_init(SMB2_IOCTL, tcon, (void **) &req);
+	rc = small_smb2_ioctl_init(opcode, tcon, (void **) &req);
 	if (rc)
 		return rc;
 
-- 
2.25.1