[PATCH 0/1] cifs: do not leak EDEADLK to dgetents64

[PATCH 0/1] cifs: do not leak EDEADLK to dgetents64

[Ronnie Sahlberg]

Steve, List

Please find a patch that stops us from leaking EDEADLK (not enough credits)
to userspace when we do not have enough credits due to a pending reconnect.
This can be triggered for example if the server responds with
STATUS_USER_SESSION_DELETED during the Create part of the Create/QueryDir
that starts a directory scan.


Easiest way to reproduce this is patching up scrambla to inject this error
every 3 directory scans:
diff --git a/server/server.py b/server/server.py
index 7fd113b..47d0b7f 100644
--- a/server/server.py
+++ b/server/server.py
@@ -26,6 +26,7 @@ from smb2.filesystem_info import *
 from smb2.dir_info import *
 from smb2.ntlmssp import *
 
+
 class File(object):
 
     def __init__(self, path, flags, at, **kwargs):
@@ -81,6 +82,7 @@ class Server(object):
     dialect = 0
     
     def __init__(self, s, **kwargs):
+        self.errc = 0
         self._s = s
         self._sesid = 1
         self._treeid = 1
@@ -348,6 +350,16 @@ class Server(object):
         #
         # Create/Open
         #
+        #print('PDU', pdu)
+        if pdu['desired_access'] == 0x81:
+            print('YEAH')
+            self.errc = self.errc + 1
+            if self.errc == 3:
+                print('Generate error')
+                self.errc = 0
+                self._compound_error = Status.INVALID_PARAMETER
+                return (Status.USER_SESSION_DELETED,
+                        ErrorResponse.encode({'error_data' : bytes(1)}))
         if not hdr['tree_id'] in self.trees:
             self._compound_error = Status.INVALID_PARAMETER
             return (self._compound_error,

[PATCH] cifs: Do not leak EDEADLK to dgetents64 for STATUS_USER_SESSION_DELETED

[Ronnie Sahlberg]

RHBZ: 1994393

If we hit a STATUS_USER_SESSION_DELETED for the Create part in the
Create/QueryDirectory compound that starts a directory scan
we will leak EDEADLK back to userspace and surprise glibc and the application.

Pick this up cifs_readdir() and retry a small number of tries before we
return an error to userspace.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
---
 fs/cifs/readdir.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/readdir.c b/fs/cifs/readdir.c
index bfee176b901d..56e5d456366d 100644
--- a/fs/cifs/readdir.c
+++ b/fs/cifs/readdir.c
@@ -930,6 +930,7 @@ int cifs_readdir(struct file *file, struct dir_context *ctx)
 	unsigned int max_len;
 	const char *full_path;
 	void *page = alloc_dentry_path();
+	int retry_count = 0;
 
 	xid = get_xid();
 
@@ -944,8 +945,15 @@ int cifs_readdir(struct file *file, struct dir_context *ctx)
 	 * '..'. Otherwise we won't be able to notify VFS in case of failure.
 	 */
 	if (file->private_data == NULL) {
+		again:
 		rc = initiate_cifs_search(xid, file, full_path);
-		cifs_dbg(FYI, "initiate cifs search rc %d\n", rc);
+		if (rc == -EDEADLK && retry_count++ < 5) {
+			/*
+			 * We don't have enough credits to start reading the
+			 * directory so just try again.
+			 */
+			goto again;
+		}
 		if (rc)
 			goto rddir2_exit;
 	}
-- 
2.30.2