@@ -7,6 +7,7 @@
* the Free Software Foundation.
*/
+#include <linux/module.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/file.h>
@@ -16,10 +17,41 @@
#include <linux/uaccess.h>
#include <linux/sched.h>
#include <linux/namei.h>
+#include <linux/fdtable.h>
+#include <linux/ratelimit.h>
#include "overlayfs.h"
#define OVL_COPY_UP_CHUNK_SIZE (1 << 20)
+static bool __read_mostly ovl_check_copy_up;
+module_param_named(check_copy_up, ovl_check_copy_up, bool,
+ S_IWUSR | S_IRUGO);
+MODULE_PARM_DESC(ovl_check_copy_up,
+ "Warn on copy-up when causing process also has a R/O fd open");
+
+static int ovl_check_fd(const void *data, struct file *f, unsigned fd)
+{
+ const struct dentry *dentry = data;
+
+ if (f->f_inode == d_inode(dentry))
+ pr_warn_ratelimited("overlayfs: Warning: Copying up %pD, but open R/O on fd %u which will cease to be coherent [pid=%d %s]\n",
+ f, fd, current->pid, current->comm);
+ return 0;
+}
+
+/*
+ * Check the fds open by this process and warn if something like the following
+ * scenario is about to occur:
+ *
+ * fd1 = open("foo", O_RDONLY);
+ * fd2 = open("foo", O_RDWR);
+ */
+static void ovl_do_check_copy_up(struct dentry *dentry)
+{
+ if (ovl_check_copy_up)
+ iterate_fd(current->files, 0, ovl_check_fd, dentry);
+}
+
int ovl_copy_xattr(struct dentry *old, struct dentry *new)
{
ssize_t list_size, size;
@@ -302,6 +334,8 @@ int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
if (WARN_ON(!workdir))
return -EROFS;
+ ovl_do_check_copy_up(lowerpath->dentry);
+
ovl_path_upper(parent, &parentpath);
upperdir = parentpath.dentry;
Print a warning when overlayfs copies up a file if the process that triggered the copy up has a R/O fd open to the lower file being copied up. This can help catch applications that do things like the following: fd1 = open("foo", O_RDONLY); fd2 = open("foo", O_RDWR); where they expect fd1 and fd2 to refer to the same file - which will no longer be the case post-copy up. With this patch, the following commands: bash 5</mnt/a/foo128 6<>/mnt/a/foo128 assuming /mnt/a/foo128 to be an un-copied up file on an overlay will produce the following warning in the kernel log: overlayfs: Copying up foo129, but open R/O on fd 5 which will cease to be coherent [pid=3818 bash] This is enabled by setting: /sys/module/overlay/parameters/check_copy_up to 1. The warnings are ratelimited and are also limited to one warning per file - assuming the copy up completes in each case. Signed-off-by: David Howells <dhowells@redhat.com> --- -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html