From: Karel Zak <kzak@redhat.com>
Date: Thu, 23 Mar 2023 14:25:00 +0000 (+0100)
Subject: libmount: fix MS_REMOUNT emulation by mount_setattr()
X-Git-Tag: v2.39-rc2~25
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=fee1ddebfc5b84d26add58eb00a304520207ed2e;p=thirdparty%2Futil-linux.git

libmount: fix MS_REMOUNT emulation by mount_setattr()

The classic mount(MS_REMOUNT) means that all unspecified MS_NOxxx
flags are remove (except MS_NOATIME). We need to follow this semantic
when emulate remount by mount_setattr(), because "mount -o remount /"
is the way how (for example) systemd resets root filesystem to default
(e.g. ro->rw, etc.)

Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=2180593
Signed-off-by: Karel Zak <kzak@redhat.com>
---

diff --git a/libmount/src/hook_mount.c b/libmount/src/hook_mount.c
index b535382b4d..39fc841d50 100644
--- a/libmount/src/hook_mount.c
+++ b/libmount/src/hook_mount.c
@@ -610,7 +610,7 @@ static int hook_prepare(struct libmnt_context *cxt,
 	/* call mount_setattr() */
 	if (!rc
 	    && cxt->helper == NULL
-	    && (set != 0 || clr != 0))
+	    && (set != 0 || clr != 0 || (flags & MS_REMOUNT)))
 		rc = mnt_context_append_hook(cxt, hs, MNT_STAGE_MOUNT, NULL,
 					hook_set_vfsflags);
 
diff --git a/libmount/src/optlist.c b/libmount/src/optlist.c
index e3b824e3bc..ede96e4354 100644
--- a/libmount/src/optlist.c
+++ b/libmount/src/optlist.c
@@ -831,6 +831,7 @@ int mnt_optlist_get_attrs(struct libmnt_optlist *ls, uint64_t *set, uint64_t *cl
 {
 	struct libmnt_iter itr;
 	struct libmnt_opt *opt;
+	uint64_t remount_reset = 0;
 
 	if (!ls || !ls->linux_map || !set || !clr)
 		return -EINVAL;
@@ -838,6 +839,19 @@ int mnt_optlist_get_attrs(struct libmnt_optlist *ls, uint64_t *set, uint64_t *cl
 	*set = 0, *clr = 0;
 	mnt_reset_iter(&itr, MNT_ITER_FORWARD);
 
+	/* The classic mount(2) MS_REMOUNT resets all flags which are not
+	 * specified (except atime stuff). For backward compatibility we need
+	 * to emulate this semantic by mount_setattr(). The new
+	 * mount_setattr() has simple set/unset sematinc and nothing is
+	 * internally in kernel reseted.
+	 */
+	if (mnt_optlist_is_remount(ls)
+	    && !mnt_optlist_is_bind(ls)
+	    && rec == MNT_OL_NOREC)
+		remount_reset = (MOUNT_ATTR_RDONLY| MOUNT_ATTR_NOSUID| \
+				 MOUNT_ATTR_NODEV | MOUNT_ATTR_NOEXEC| \
+				 MOUNT_ATTR_NOSYMFOLLOW);
+
 	while (mnt_optlist_next_opt(ls, &itr, &opt) == 0) {
 		uint64_t x = 0;
 
@@ -856,6 +870,9 @@ int mnt_optlist_get_attrs(struct libmnt_optlist *ls, uint64_t *set, uint64_t *cl
 		if (flag_to_attr( opt->ent->id, &x) < 0)
 			continue;
 
+		if (x && remount_reset)
+			remount_reset &= ~x;
+
 		if (opt->ent->mask & MNT_INVERT) {
 			DBG(OPTLIST, ul_debugobj(ls, " clr: %s", opt->ent->name));
 			*clr |= x;
@@ -869,6 +886,9 @@ int mnt_optlist_get_attrs(struct libmnt_optlist *ls, uint64_t *set, uint64_t *cl
 		}
 	}
 
+	if (remount_reset)
+		*clr |= remount_reset;
+
 	DBG(OPTLIST, ul_debugobj(ls, "return attrs set=0x%08" PRIx64
 				      ", clr=0x%08" PRIx64 " %s",
 				*set, *clr,