release/5.2.22/CIFS-Fix-use-after-free-of-file-info-structures.patch

From d6b94584b9a7f11c5e9ea09520741baa8a1ff732 Mon Sep 17 00:00:00 2001
From: Pavel Shilovsky <pshilov@microsoft.com>
Date: Wed, 23 Oct 2019 15:37:19 -0700
Subject: [PATCH] CIFS: Fix use after free of file info structures

commit 1a67c415965752879e2e9fad407bc44fc7f25f23 upstream.

Currently the code assumes that if a file info entry belongs
to lists of open file handles of an inode and a tcon then
it has non-zero reference. The recent changes broke that
assumption when putting the last reference of the file info.
There may be a situation when a file is being deleted but
nothing prevents another thread to reference it again
and start using it. This happens because we do not hold
the inode list lock while checking the number of references
of the file info structure. Fix this by doing the proper
locking when doing the check.

Fixes: 487317c99477d ("cifs: add spinlock for the openFileList to cifsInodeInfo")
Fixes: cb248819d209d ("cifs: use cifsInodeInfo->open_file_lock while iterating to avoid a panic")
Cc: Stable <stable@vger.kernel.org>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 4c1aeb2cf7f5..53dbb6e0d390 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -405,10 +405,11 @@ void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
 	bool oplock_break_cancelled;
 
 	spin_lock(&tcon->open_file_lock);
-
+	spin_lock(&cifsi->open_file_lock);
 	spin_lock(&cifs_file->file_info_lock);
 	if (--cifs_file->count > 0) {
 		spin_unlock(&cifs_file->file_info_lock);
+		spin_unlock(&cifsi->open_file_lock);
 		spin_unlock(&tcon->open_file_lock);
 		return;
 	}
@@ -421,9 +422,7 @@ void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
 	cifs_add_pending_open_locked(&fid, cifs_file->tlink, &open);
 
 	/* remove it from the lists */
-	spin_lock(&cifsi->open_file_lock);
 	list_del(&cifs_file->flist);
-	spin_unlock(&cifsi->open_file_lock);
 	list_del(&cifs_file->tlist);
 	atomic_dec(&tcon->num_local_opens);
 
@@ -440,6 +439,7 @@ void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
 		cifs_set_oplock_level(cifsi, 0);
 	}
 
+	spin_unlock(&cifsi->open_file_lock);
 	spin_unlock(&tcon->open_file_lock);
 
 	oplock_break_cancelled = wait_oplock_handler ?
-- 
2.7.4