util linux patches
Signed-off-by: basebuilder_pel7ppc64bebuilder0 <basebuilder@powerel.org>master
basebuilder_pel7ppc64bebuilder0
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From 2218dc0d130bb72809e2d8b26a36402bf6293727 Mon Sep 17 00:00:00 2001
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From: Karel Zak <kzak@redhat.com>
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Date: Mon, 17 Aug 2015 11:54:26 +0200
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Subject: [PATCH 84/86] libmount: add support for "bind,ro"
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Now it's necessary to use two mount(8) calls to create a read-only
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mount:
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mount /foo /bar -o bind
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mount /bar -o remount,ro,bind
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This patch allows to specify "bind,ro" and the remount is done
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automatically by libmount by additional mount(2) syscall. It's not
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atomic of course.
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Addresses: http://bugzilla.redhat.com/show_bug.cgi?id=1281839
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Signed-off-by: Karel Zak <kzak@redhat.com>
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---
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libmount/src/context_mount.c | 46 ++++++++++++++++++++++++++++++++++++++++++++
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sys-utils/mount.8 | 37 ++++++++++++++++++-----------------
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2 files changed, 65 insertions(+), 18 deletions(-)
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diff --git a/libmount/src/context_mount.c b/libmount/src/context_mount.c
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index d6691eb..4df2646 100644
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--- a/libmount/src/context_mount.c
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+++ b/libmount/src/context_mount.c
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@@ -62,6 +62,10 @@ static int mnt_context_append_additional_mount(struct libmnt_context *cxt,
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return 0;
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}
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+/*
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+ * add additional mount(2) syscall requests when necessary to set propagation flags
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+ * after regular mount(2).
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+ */
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static int init_propagation(struct libmnt_context *cxt)
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{
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char *name;
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@@ -102,6 +106,41 @@ static int init_propagation(struct libmnt_context *cxt)
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}
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/*
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+ * add additional mount(2) syscall request to implement "ro,bind", the first regular
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+ * mount(2) is the "bind" operation, the second is "remount,ro,bind" call.
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+ *
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+ * Note that we don't remove "ro" from the first syscall (kernel silently
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+ * ignores this flags for bind operation) -- maybe one day kernel will support
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+ * read-only binds in one step and then all will be done by the firts mount(2) and the
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+ * second remount will be noop...
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+ */
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+static int init_robind(struct libmnt_context *cxt)
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+{
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+ struct libmnt_addmount *ad;
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+ int rc;
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+
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+ assert(cxt);
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+ assert(cxt->mountflags & MS_BIND);
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+ assert(cxt->mountflags & MS_RDONLY);
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+ assert(!(cxt->mountflags & MS_REMOUNT));
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+
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+ DBG(CXT, mnt_debug_h(cxt, "mount: initialize additional ro,bind mount"));
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+
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+ ad = mnt_new_addmount();
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+ if (!ad)
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+ return -ENOMEM;
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+
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+ ad->mountflags = MS_REMOUNT | MS_BIND | MS_RDONLY;
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+ if (cxt->mountflags & MS_REC)
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+ ad->mountflags |= MS_REC;
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+ rc = mnt_context_append_additional_mount(cxt, ad);
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+ if (rc)
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+ return rc;
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+
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+ return 0;
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+}
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+
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+/*
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* this has to be called after mnt_context_evaluate_permissions()
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*/
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static int fix_optstr(struct libmnt_context *cxt)
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@@ -174,6 +213,13 @@ static int fix_optstr(struct libmnt_context *cxt)
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if (rc)
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return rc;
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}
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+ if ((cxt->mountflags & MS_BIND)
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+ && (cxt->mountflags & MS_RDONLY)
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+ && !(cxt->mountflags & MS_REMOUNT)) {
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+ rc = init_robind(cxt);
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+ if (rc)
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+ return rc;
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+ }
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next = fs->fs_optstr;
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diff --git a/sys-utils/mount.8 b/sys-utils/mount.8
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index 3648870..49cb281 100644
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--- a/sys-utils/mount.8
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+++ b/sys-utils/mount.8
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@@ -388,25 +388,25 @@ or shortoption
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.\" available since Linux 2.4.11.
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Note that the filesystem mount options will remain the same as those
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-on the original mount point, and cannot be changed by passing the -o
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-option along with --bind/--rbind. The mount options can be
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-changed by a separate remount command, for example:
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+on the original mount point.
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+
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+.BR mount(8)
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+since v2.27 (backported to RHEL7.3) allow to change the options by passing the
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+.B \-o
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+option along with
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+.BR \-\-bind
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+for example:
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.RS
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.br
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-.B mount --bind
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-.I olddir newdir
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-.br
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-.B mount -o remount,ro
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-.I newdir
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+.B mount \-\-bind,ro foo foo
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.RE
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-Note that behavior of the remount operation depends on the /etc/mtab file. The
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-first command stores the 'bind' flag to the /etc/mtab file and the second
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-command reads the flag from the file. If you have a system without the
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-/etc/mtab file or if you explicitly define source and target for the remount
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-command (then mount(8) does not read /etc/mtab), then you have to use bind flag
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-(or option) for the remount command too. For example:
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+This feature is not supported by Linux kernel and it is implemented in userspace
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+by additional remount mount(2) syscall. This solution is not atomic.
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+
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+The alternative (classic) way to create a read-only bind mount is to use remount
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+operation, for example:
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.RS
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.br
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@@ -417,14 +417,15 @@ command (then mount(8) does not read /etc/mtab), then you have to use bind flag
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.I olddir newdir
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.RE
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-Note that
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-.I remount,ro,bind
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-will create a read-only mountpoint (VFS entry), but the original filesystem suberblock
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-will be still writable, it means that the
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+Note that read-only bind will create a read-only mountpoint (VFS entry), but the
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+original filesystem superblock will still be writable, meaning that the
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.I olddir
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will be writable, but the
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.I newdir
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will be read-only.
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+
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+It's impossible to change mount options recursively
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+(for example with \fB -o rbind,ro\fR).
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.RE
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.B The move operation.
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--
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2.7.4
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