Commit 069ddcda authored Jun 11, 2012 by Tyler Hicks

eCryptfs: Copy up POSIX ACL and read-only flags from lower mount

When the eCryptfs mount options do not include '-o acl', but the lower
filesystem's mount options do include 'acl', the MS_POSIXACL flag is not
flipped on in the eCryptfs super block flags. This flag is what the VFS
checks in do_last() when deciding if the current umask should be applied
to a newly created inode's mode or not. When a default POSIX ACL mask is
set on a directory, the current umask is incorrectly applied to new
inodes created in the directory. This patch ignores the MS_POSIXACL flag
passed into ecryptfs_mount() and sets the flag on the eCryptfs super
block depending on the flag's presence on the lower super block.

Additionally, it is incorrect to allow a writeable eCryptfs mount on top
of a read-only lower mount. This missing check did not allow writes to
the read-only lower mount because permissions checks are still performed
on the lower filesystem's objects but it is best to simply not allow a
rw mount on top of ro mount. However, a ro eCryptfs mount on top of a rw
mount is valid and still allowed.

https://launchpad.net/bugs/1009207

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Reported-by: Stefan Beller <stefanbeller@googlemail.com>
Cc: John Johansen <john.johansen@canonical.com>

parent bd0a521e

fs/ecryptfs/main.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -505,7 +505,6 @@ static struct dentry ecryptfs_mount(struct file_system_type fs_type, int flags
		goto out;
		}

		s->s_flags = flags;
		rc = bdi_setup_and_register(&sbi->bdi, "ecryptfs", BDI_CAP_MAP_COPY);
		if (rc)
		goto out1;
		@@ -541,6 +540,15 @@ static struct dentry ecryptfs_mount(struct file_system_type fs_type, int flags
		}

		ecryptfs_set_superblock_lower(s, path.dentry->d_sb);

		/**
		* Set the POSIX ACL flag based on whether they're enabled in the lower
		* mount. Force a read-only eCryptfs mount if the lower mount is ro.
		* Allow a ro eCryptfs mount even when the lower mount is rw.
		*/
		s->s_flags = flags & ~MS_POSIXACL;
		s->s_flags \|= path.dentry->d_sb->s_flags & (MS_RDONLY \| MS_POSIXACL);

		s->s_maxbytes = path.dentry->d_sb->s_maxbytes;
		s->s_blocksize = path.dentry->d_sb->s_blocksize;
		s->s_magic = ECRYPTFS_SUPER_MAGIC;

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