diff mbox series

[J/hwe-5.17,2/2] UBUNTU: SAUCE: overlayfs: fix incorrect mnt_id of files opened from map_files

Message ID 20220805063214.32432-6-andrea.righi@canonical.com
State New
Headers show
Series None | expand

Commit Message

Andrea Righi Aug. 5, 2022, 6:32 a.m. UTC 
From: Alexander Mikhalitsyn <alexander@mihalicyn.com>

BugLink: https://bugs.launchpad.net/bugs/1983640

The hack was introduced in ("UBUNTU: SAUCE: overlayfs: allow with
shiftfs as underlay") and it broke checkpoint/restore of docker
contains:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1857257

The following script can be used to trigger the issue:
  #!/bin/bash

  cat > test.py << EOF
  import sys

  f = open("/proc/self/maps")

  for l in f.readlines():
    if "python" not in l:
      continue
    print(l)
    s = l.split()
    start, end = s[0].split("-")
    fname = s[-1]
    print(start, end, fname)
    break
  else:
    sys.exit(1)

  test_file1 = open(fname)
  test_file2 = open("/proc/self/map_files/%s-%s" % (start, end))

  fdinfo1 = open("/proc/self/fdinfo/%d" % test_file1.fileno()).read()
  fdinfo2 = open("/proc/self/fdinfo/%d" % test_file2.fileno()).read()

  if fdinfo1 != fdinfo2:
    print("FAIL")
    print(test_file1)
    print(fdinfo1)
    print(test_file2)
    print(fdinfo2)
    sys.exit(1)
  print("PASS")
  EOF
  sudo docker run -it --privileged --rm -v `pwd`:/mnt python python /mnt/test.py

Thanks to Andrei Vagin for the reproducer and investigation of this problem.

[refactoring to drop dependency of AUFS]
Signed-off-by: Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
---
 fs/overlayfs/file.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)
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Patch

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 835e99b2e080..c0bae39ae4e2 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -490,6 +490,32 @@  static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 	return ret;
 }
 
+/*
+ * In map_files_get_link() (fs/proc/base.c)
+ * we need to determine correct path from overlayfs.
+ * But real_mount(realfile->f_path.mnt) may be not
+ * equal to real_mount(file->f_path.mnt). In such case
+ * fdinfo of the same file which was opened from
+ * /proc/<pid>/map_files/... and "usual" path
+ * will show different mnt_id.
+ *
+ * We solve issue like in aufs by using additional
+ * field on struct vm_area_struct called "vm_prfile"
+ * which is used only for fdinfo/"printing" needs.
+ *
+ * See also mm/prfile.c
+ */
+static void ovl_vm_prfile_set(struct vm_area_struct *vma,
+			      struct file *file)
+{
+	get_file(file);
+	vma->vm_prfile = file;
+#ifndef CONFIG_MMU
+	get_file(file);
+	vma->vm_region->vm_prfile = file;
+#endif
+}
+
 static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 {
 	struct file *realfile = file->private_data;
@@ -507,6 +533,10 @@  static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 	old_cred = ovl_override_creds(file_inode(file)->i_sb);
 	ret = call_mmap(vma->vm_file, vma);
 	revert_creds(old_cred);
+
+	if (!ret)
+		ovl_vm_prfile_set(vma, file);
+
 	ovl_file_accessed(file);
 
 	return ret;