This is a note to let you know that I've just added the patch titled
cifs: fix use-after-free bug in find_writable_file
to the 3.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
cifs-fix-use-after-free-bug-in-find_writable_file.patch
and it can be found in the queue-3.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From e1e9bda22d7ddf88515e8fe401887e313922823e Mon Sep 17 00:00:00 2001
From: David Disseldorp <[email protected]>
Date: Fri, 13 Mar 2015 14:20:29 +0100
Subject: cifs: fix use-after-free bug in find_writable_file
From: David Disseldorp <[email protected]>
commit e1e9bda22d7ddf88515e8fe401887e313922823e upstream.
Under intermittent network outages, find_writable_file() is susceptible
to the following race condition, which results in a user-after-free in
the cifs_writepages code-path:
Thread 1 Thread 2
======== ========
inv_file = NULL
refind = 0
spin_lock(&cifs_file_list_lock)
// invalidHandle found on openFileList
inv_file = open_file
// inv_file->count currently 1
cifsFileInfo_get(inv_file)
// inv_file->count = 2
spin_unlock(&cifs_file_list_lock);
cifs_reopen_file() cifs_close()
// fails (rc != 0) ->cifsFileInfo_put()
spin_lock(&cifs_file_list_lock)
// inv_file->count = 1
spin_unlock(&cifs_file_list_lock)
spin_lock(&cifs_file_list_lock);
list_move_tail(&inv_file->flist,
&cifs_inode->openFileList);
spin_unlock(&cifs_file_list_lock);
cifsFileInfo_put(inv_file);
->spin_lock(&cifs_file_list_lock)
// inv_file->count = 0
list_del(&cifs_file->flist);
// cleanup!!
kfree(cifs_file);
spin_unlock(&cifs_file_list_lock);
spin_lock(&cifs_file_list_lock);
++refind;
// refind = 1
goto refind_writable;
At this point we loop back through with an invalid inv_file pointer
and a refind value of 1. On second pass, inv_file is not overwritten on
openFileList traversal, and is subsequently dereferenced.
Signed-off-by: David Disseldorp <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: Steve French <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
fs/cifs/file.c | 1 +
1 file changed, 1 insertion(+)
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1829,6 +1829,7 @@ refind_writable:
cifsFileInfo_put(inv_file);
spin_lock(&cifs_file_list_lock);
++refind;
+ inv_file = NULL;
goto refind_writable;
}
}
Patches currently in stable-queue which might be from [email protected] are
queue-3.19/cifs-fix-use-after-free-bug-in-find_writable_file.patch
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