From 1b2d8187360157b00b47f52522fc039d82e34e6b Mon Sep 17 00:00:00 2001 From: Karel Zak Date: Thu, 3 Aug 2023 11:43:28 +0200 Subject: [PATCH] libmount: don't canonicalize symlinks for bind operation The new kernel mount API can bind over symlink by default. Unfortunately, libmount always canonicalizes all paths (due to backward compatibility, search in mountinfo, search in fstab, etc.). Possible workaround is -c, --no-canonicalize but it disable all paths canonicalization, tags to paths conversions etc. This patch disables the canonicalization only for the target path (if symlink) on bind operation. Fixes: https://github.com/util-linux/util-linux/issues/2370 Signed-off-by: Karel Zak --- libmount/src/context_mount.c | 6 +++++- sys-utils/mount.8.adoc | 6 +++++- 2 files changed, 10 insertions(+), 2 deletions(-) diff --git a/libmount/src/context_mount.c b/libmount/src/context_mount.c index 05c84f1702..5aec87d6c3 100644 --- a/libmount/src/context_mount.c +++ b/libmount/src/context_mount.c @@ -669,6 +669,7 @@ static int prepare_target(struct libmnt_context *cxt) const char *tgt, *prefix; int rc = 0; struct libmnt_ns *ns_old; + struct stat st; assert(cxt); assert(cxt->fs); @@ -708,7 +709,10 @@ static int prepare_target(struct libmnt_context *cxt) return -MNT_ERR_NAMESPACE; /* canonicalize the path */ - if (rc == 0) { + if (rc == 0 && + !(cxt->optlist && mnt_optlist_is_bind(cxt->optlist) + && mnt_safe_lstat(tgt, &st) == 0 && S_ISLNK(st.st_mode))) { + struct libmnt_cache *cache = mnt_context_get_cache(cxt); if (cache) { diff --git a/sys-utils/mount.8.adoc b/sys-utils/mount.8.adoc index 74d2960e54..6479efd649 100644 --- a/sys-utils/mount.8.adoc +++ b/sys-utils/mount.8.adoc @@ -240,6 +240,8 @@ It's also possible to change nosuid, nodev, noexec, noatime, nodiratime, relatim Since util-linux 2.31, *mount* ignores the *bind* flag from _/etc/fstab_ on a *remount* operation (if *-o remount* is specified on command line). This is necessary to fully control mount options on remount by command line. In previous versions the bind flag has been always applied and it was impossible to re-define mount options without interaction with the bind semantic. This *mount* behavior does not affect situations when "remount,bind" is specified in the _/etc/fstab_ file. +Since util-linux 2.40, *mount* does not canonicalize the mountpoint path on bind operation if the target is a symlink. This feature is usable (only) with the new kernel mount API where *bind mount over symlinks* is supported. + === The move operation Move a *mounted tree* to another place (atomically). The call is: @@ -317,7 +319,9 @@ Note that it is a bad practice to use *mount -a* for _fstab_ checking. The recom Remount a subtree somewhere else (so that its contents are available in both places). See above, under *Bind mount operation*. *-c*, *--no-canonicalize*:: -Don't canonicalize paths. The *mount* command canonicalizes all paths (from the command line or _fstab_) by default. This option can be used together with the *-f* flag for already canonicalized absolute paths. The option is designed for mount helpers which call *mount -i*. It is strongly recommended to not use this command-line option for normal mount operations. +Don't canonicalize paths. The *mount* command canonicalizes all paths (from the command line or _fstab_) by default. The option is designed for mount helpers which call *mount -i*. It is strongly recommended to not use this command-line option for normal mount operations. ++ +Since util-linux 2.40, mount does not canonicalize the mountpoint path on bind operation if the target is a symlink (see "*Bind mount operation*" section for more details). + Note that *mount* does not pass this option to the **/sbin/mount.**__type__ helpers. -- 2.47.2