| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.19 077/101] cifs: fix use-after-free bug in find_writable_file | Date | Fri, 17 Apr 2015 15:29:05 +0200 |
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3.19-stable review patch. If anyone has any objections, please let me know.
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From: David Disseldorp <ddiss@suse.de>
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 <ddiss@suse.de> Reviewed-by: Jeff Layton <jlayton@samba.org> Signed-off-by: Steve French <smfrench@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- 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; } }
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