eCryptfs: Copy up POSIX ACL and read-only flags from lower mount
From: Tyler Hicks <firstname.lastname@example.org>
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.
Signed-off-by: Tyler Hicks <email@example.com>
Reported-by: Stefan Beller <firstname.lastname@example.org>
Cc: John Johansen <email@example.com>
(cherry picked from commit 069ddcda37b2cf5bb4b6031a944c0e9359213262)
fs/ecryptfs/main.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
+ * 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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