From 7c6e984dfca8ff5b04d359a59b24f39a691b87d3 Mon Sep 17 00:00:00 2001 From: Roman Borisov Date: Wed, 25 May 2011 16:26:48 -0700 Subject: [PATCH] fs/namespace.c: bound mount propagation fix This issue was discovered by users of busybox. And the bug is actual for busybox users, I don't know how it affects others. Apparently, mount is called with and without MS_SILENT, and this affects mount() behaviour. But MS_SILENT is only supposed to affect kernel logging verbosity. The following script was run in an empty test directory: mkdir -p mount.dir mount.shared1 mount.shared2 touch mount.dir/a mount.dir/b mount -vv --bind mount.shared1 mount.shared1 mount -vv --make-rshared mount.shared1 mount -vv --bind mount.shared2 mount.shared2 mount -vv --make-rshared mount.shared2 mount -vv --bind mount.shared2 mount.shared1 mount -vv --bind mount.dir mount.shared2 ls -R mount.dir mount.shared1 mount.shared2 umount mount.dir mount.shared1 mount.shared2 2>/dev/null umount mount.dir mount.shared1 mount.shared2 2>/dev/null umount mount.dir mount.shared1 mount.shared2 2>/dev/null rm -f mount.dir/a mount.dir/b mount.dir/c rmdir mount.dir mount.shared1 mount.shared2 mount -vv was used to show the mount() call arguments and result. Output shows that flag argument has 0x00008000 = MS_SILENT bit: mount: mount('mount.shared1','mount.shared1','(null)',0x00009000,'(null)'):0 mount: mount('','mount.shared1','',0x0010c000,''):0 mount: mount('mount.shared2','mount.shared2','(null)',0x00009000,'(null)'):0 mount: mount('','mount.shared2','',0x0010c000,''):0 mount: mount('mount.shared2','mount.shared1','(null)',0x00009000,'(null)'):0 mount: mount('mount.dir','mount.shared2','(null)',0x00009000,'(null)'):0 mount.dir: a b mount.shared1: mount.shared2: a b After adding --loud option to remove MS_SILENT bit from just one mount cmd: mkdir -p mount.dir mount.shared1 mount.shared2 touch mount.dir/a mount.dir/b mount -vv --bind mount.shared1 mount.shared1 2>&1 mount -vv --make-rshared mount.shared1 2>&1 mount -vv --bind mount.shared2 mount.shared2 2>&1 mount -vv --loud --make-rshared mount.shared2 2>&1 # <-HERE mount -vv --bind mount.shared2 mount.shared1 2>&1 mount -vv --bind mount.dir mount.shared2 2>&1 ls -R mount.dir mount.shared1 mount.shared2 2>&1 umount mount.dir mount.shared1 mount.shared2 2>/dev/null umount mount.dir mount.shared1 mount.shared2 2>/dev/null umount mount.dir mount.shared1 mount.shared2 2>/dev/null rm -f mount.dir/a mount.dir/b mount.dir/c rmdir mount.dir mount.shared1 mount.shared2 The result is different now - look closely at mount.shared1 directory listing. Now it does show files 'a' and 'b': mount: mount('mount.shared1','mount.shared1','(null)',0x00009000,'(null)'):0 mount: mount('','mount.shared1','',0x0010c000,''):0 mount: mount('mount.shared2','mount.shared2','(null)',0x00009000,'(null)'):0 mount: mount('','mount.shared2','',0x00104000,''):0 mount: mount('mount.shared2','mount.shared1','(null)',0x00009000,'(null)'):0 mount: mount('mount.dir','mount.shared2','(null)',0x00009000,'(null)'):0 mount.dir: a b mount.shared1: a b mount.shared2: a b The analysis shows that MS_SILENT flag which is ON by default in any busybox-> mount operations cames to flags_to_propagation_type function and causes the error return while is_power_of_2 checking because the function expects only one bit set. This doesn't allow to do busybox->mount with any --make-[r]shared, --make-[r]private etc options. Moreover, the recently added flags_to_propagation_type() function doesn't allow us to do such operations as --make-[r]private --make-[r]shared etc. when MS_SILENT is on. The idea or clearing the MS_SILENT flag came from to Denys Vlasenko. Signed-off-by: Roman Borisov Reported-by: Denys Vlasenko Cc: Chuck Ebbert Cc: Alexander Shishkin Cc: Al Viro Cc: Christoph Hellwig Signed-off-by: Andrew Morton Signed-off-by: Al Viro --- fs/namespace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/namespace.c b/fs/namespace.c index d99bcf59e4c2..fe59bd145d21 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1695,7 +1695,7 @@ static int graft_tree(struct vfsmount *mnt, struct path *path) static int flags_to_propagation_type(int flags) { - int type = flags & ~MS_REC; + int type = flags & ~(MS_REC | MS_SILENT); /* Fail if any non-propagation flags are set */ if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE)) -- 2.20.1