From 8681757ee08361d78e4c74da8abae9d6df8623e7 Mon Sep 17 00:00:00 2001 From: Karel Zak Date: Mon, 28 May 2018 15:46:28 +0200 Subject: [PATCH 62/63] libmount: accept another flags on MS_REMOUNT|MS_BIND The current libmount MS_REMOUNT|MS_BIND support is restricted to MS_RDONLY (read-only bind mount). This is too restrictive as Linux kernel supports bind-remount for arbitrary VFS flags. After this update you can use # mount /dev/sdc1 /mnt/A # mount --bind -onosuid,noexec /mnt/A /mnt/B # findmnt /dev/sdc1 -oTARGET,SOURCE,FS-OPTIONS,VFS-OPTIONS TARGET SOURCE FS-OPTIONS VFS-OPTIONS /mnt/A /dev/sdc1 rw,stripe=512,data=ordered rw,relatime /mnt/B /dev/sdc1 rw,stripe=512,data=ordered rw,nosuid,noexec,relatime The "mount --bind" is composed from two syscalls of course (1st is bind, 2nd is bind,remount,nosuid,noexec). Addresses: https://github.com/karelzak/util-linux/issues/637 Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=1919529 Upstream: http://github.com/karelzak/util-linux/commit/e82b77e9696a6dada96a7f3ea3ec20a63e8e7b9e Signed-off-by: Karel Zak --- libmount/src/context_mount.c | 22 ++++++++-------------- libmount/src/mountP.h | 3 +++ sys-utils/mount.8 | 5 +++-- 3 files changed, 14 insertions(+), 16 deletions(-) diff --git a/libmount/src/context_mount.c b/libmount/src/context_mount.c index a6de36178..b88e60507 100644 --- a/libmount/src/context_mount.c +++ b/libmount/src/context_mount.c @@ -107,22 +107,16 @@ static int init_propagation(struct libmnt_context *cxt) } /* - * add additional mount(2) syscall request to implement "ro,bind", the first regular - * mount(2) is the "bind" operation, the second is "remount,ro,bind" call. - * - * Note that we don't remove "ro" from the first syscall (kernel silently - * ignores this flags for bind operation) -- maybe one day kernel will support - * read-only binds in one step and then all will be done by the first mount(2) and the - * second remount will be noop... + * add additional mount(2) syscall request to implement "bind,", the first regular + * mount(2) is the "bind" operation, the second is "remount,bind," call. */ -static int init_robind(struct libmnt_context *cxt) +static int init_bind_remount(struct libmnt_context *cxt) { struct libmnt_addmount *ad; int rc; assert(cxt); assert(cxt->mountflags & MS_BIND); - assert(cxt->mountflags & MS_RDONLY); assert(!(cxt->mountflags & MS_REMOUNT)); DBG(CXT, ul_debugobj(cxt, "mount: initialize additional ro,bind mount")); @@ -131,9 +125,9 @@ static int init_robind(struct libmnt_context *cxt) if (!ad) return -ENOMEM; - ad->mountflags = MS_REMOUNT | MS_BIND | MS_RDONLY; - if (cxt->mountflags & MS_REC) - ad->mountflags |= MS_REC; + ad->mountflags = cxt->mountflags; + ad->mountflags |= (MS_REMOUNT | MS_BIND); + rc = mnt_context_append_additional_mount(cxt, ad); if (rc) return rc; @@ -254,9 +248,9 @@ static int fix_optstr(struct libmnt_context *cxt) return rc; } if ((cxt->mountflags & MS_BIND) - && (cxt->mountflags & MS_RDONLY) + && (cxt->mountflags & MNT_BIND_SETTABLE) && !(cxt->mountflags & MS_REMOUNT)) { - rc = init_robind(cxt); + rc = init_bind_remount(cxt); if (rc) return rc; } diff --git a/libmount/src/mountP.h b/libmount/src/mountP.h index 52a238ef3..64a507e61 100644 --- a/libmount/src/mountP.h +++ b/libmount/src/mountP.h @@ -363,6 +363,9 @@ struct libmnt_context /* default flags */ #define MNT_FL_DEFAULT 0 +/* Flags usable with MS_BIND|MS_REMOUNT */ +#define MNT_BIND_SETTABLE (MS_NOSUID|MS_NODEV|MS_NOEXEC|MS_NOATIME|MS_NODIRATIME|MS_RELATIME|MS_RDONLY) + /* lock.c */ extern int mnt_lock_use_simplelock(struct libmnt_lock *ml, int enable); diff --git a/sys-utils/mount.8 b/sys-utils/mount.8 index a4d7de2c0..291e65cb1 100644 --- a/sys-utils/mount.8 +++ b/sys-utils/mount.8 @@ -410,8 +410,9 @@ will be writable, but the will be read-only. It's also possible to change nosuid, nodev, noexec, noatime, nodiratime and -relatime VFS entry flags by "remount,bind" operation. It's impossible to change -mount options recursively (for example with \fB-o rbind,ro\fR). +relatime VFS entry flags by "remount,bind" operation. The another (for example +filesystem specific flags) are silently ignored. It's impossible to change mount +options recursively (for example with \fB-o rbind,ro\fR). .BR mount (8) since v2.31 ignores the \fBbind\fR flag from -- 2.31.1