From 2b99ee2526ae61be761b0e31c50e106dbec5e9e4 Mon Sep 17 00:00:00 2001
From: Filipe Manana <fdmanana@kernel.org>
Date: Thu, 17 Aug 2023 10:20:13 +0100
Subject: [PATCH] libmount: Fix regression when mounting with atime

A regression was introduced in v2.39 that causes mounting with the atime
option to fail:

  $ mkfs.ext4 -F /dev/sdi
  $ mount -o atime /dev/sdi /mnt/sdi
  mount: /mnt/sdi: not mount point or bad option.
         dmesg(1) may have more information after failed mount system call.

The failure comes from the mount_setattr(2) call returning -EINVAL. This
is because we pass an invalid value for the attr_clr argument. From a
strace capture we have:

  mount_setattr(4, "", AT_EMPTY_PATH, {attr_set=0, attr_clr=MOUNT_ATTR_NOATIME, propagation=0 /* MS_??? */, userns_fd=0}, 32) = -1 EINVAL (Invalid argument)

We can't pass MOUNT_ATTR_NOATIME to mount_setattr(2) through the attr_clr
argument because all atime options are exclusive, so in order to set atime
one has to pass MOUNT_ATTR__ATIME to attr_clr and leave attr_set as
MOUNT_ATTR_RELATIME (which is defined as a value of 0).

This can be read from the man page for mount_setattr(2) and also from the
kernel source:

  $ cat fs/namespace.c
  static int build_mount_kattr(const struct mount_attr *attr, size_t usize,
                               struct mount_kattr *kattr, unsigned int flags)
  {
      (...)
      /*
       * Since the MOUNT_ATTR_<atime> values are an enum, not a bitmap,
       * users wanting to transition to a different atime setting cannot
       * simply specify the atime setting in @attr_set, but must also
       * specify MOUNT_ATTR__ATIME in the @attr_clr field.
       * So ensure that MOUNT_ATTR__ATIME can't be partially set in
       * @attr_clr and that @attr_set can't have any atime bits set if
       * MOUNT_ATTR__ATIME isn't set in @attr_clr.
       */
      if (attr->attr_clr & MOUNT_ATTR__ATIME) {
          if ((attr->attr_clr & MOUNT_ATTR__ATIME) != MOUNT_ATTR__ATIME)
              return -EINVAL;

              /*
               * Clear all previous time settings as they are mutually
               * exclusive.
               */
              kattr->attr_clr |= MNT_RELATIME | MNT_NOATIME;
              switch (attr->attr_set & MOUNT_ATTR__ATIME) {
              case MOUNT_ATTR_RELATIME:
                  kattr->attr_set |= MNT_RELATIME;
                  break;
              case MOUNT_ATTR_NOATIME:
                  kattr->attr_set |= MNT_NOATIME;
                  break;
              case MOUNT_ATTR_STRICTATIME:
                  break;
              default:
                  return -EINVAL;
              }
    (...)

So fix this by setting attr_clr MOUNT_ATTR__ATIME if we want to clear any
atime related option.

Signed-off-by: Filipe Manana <fdmanana@kernel.org>
---
 libmount/src/optlist.c                      | 13 ++++++++++++-
 tests/expected/libmount/context-mount-flags |  3 +++
 tests/ts/libmount/context                   |  9 ++++++++-
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/libmount/src/optlist.c b/libmount/src/optlist.c
index e93810b47..d0afc94f7 100644
--- a/libmount/src/optlist.c
+++ b/libmount/src/optlist.c
@@ -875,7 +875,18 @@ int mnt_optlist_get_attrs(struct libmnt_optlist *ls, uint64_t *set, uint64_t *cl
 
 		if (opt->ent->mask & MNT_INVERT) {
 			DBG(OPTLIST, ul_debugobj(ls, " clr: %s", opt->ent->name));
-			*clr |= x;
+			/*
+			 * All atime settings are mutually exclusive so *clr must
+			 * have MOUNT_ATTR__ATIME set.
+			 *
+			 * See the function fs/namespace.c:build_mount_kattr()
+			 * in the linux kernel source.
+			 */
+			if (x == MOUNT_ATTR_RELATIME || x == MOUNT_ATTR_NOATIME ||
+			    x == MOUNT_ATTR_STRICTATIME)
+				*clr |= MOUNT_ATTR__ATIME;
+			else
+				*clr |= x;
 		} else {
 			DBG(OPTLIST, ul_debugobj(ls, " set: %s", opt->ent->name));
 			*set |= x;
diff --git a/tests/expected/libmount/context-mount-flags b/tests/expected/libmount/context-mount-flags
index 960641863..eb71323dd 100644
--- a/tests/expected/libmount/context-mount-flags
+++ b/tests/expected/libmount/context-mount-flags
@@ -3,3 +3,6 @@ ro,nosuid,noexec
 successfully mounted
 rw,nosuid,noexec
 successfully umounted
+successfully mounted
+rw,relatime
+successfully umounted
diff --git a/tests/ts/libmount/context b/tests/ts/libmount/context
index f5b47185e..a5d2e81a3 100755
--- a/tests/ts/libmount/context
+++ b/tests/ts/libmount/context
@@ -116,8 +116,15 @@ $TS_CMD_FINDMNT --kernel --mountpoint $MOUNTPOINT -o VFS-OPTIONS -n >> $TS_OUTPU
 
 ts_run $TESTPROG --umount $MOUNTPOINT >> $TS_OUTPUT 2>> $TS_ERRLOG
 is_mounted $DEVICE && echo "$DEVICE still mounted" >> $TS_OUTPUT 2>> $TS_ERRLOG
-ts_finalize_subtest
 
+# Test that the atime option works after the migration to use the new kernel mount APIs.
+ts_run $TESTPROG --mount -o atime $DEVICE $MOUNTPOINT >> $TS_OUTPUT 2>> $TS_ERRLOG
+$TS_CMD_FINDMNT --kernel --mountpoint $MOUNTPOINT -o VFS-OPTIONS -n >> $TS_OUTPUT 2>> $TS_ERRLOG
+is_mounted $DEVICE || echo "$DEVICE not mounted" >> $TS_OUTPUT 2>> $TS_ERRLOG
+ts_run $TESTPROG --umount $MOUNTPOINT >> $TS_OUTPUT 2>> $TS_ERRLOG
+is_mounted $DEVICE && echo "$DEVICE still mounted" >> $TS_OUTPUT 2>> $TS_ERRLOG
+
+ts_finalize_subtest
 
 ts_init_subtest "mount-loopdev"
 mkdir -p $MOUNTPOINT &> /dev/null
-- 
2.33.0

