Re: [PATCH 1/4] Cache xattr security drop check for write v2

Al Viro
2011-05-31T20:08:00Z

On Tue, May 31, 2011 at 07:42:26PM +0100, Steven Whitehouse wrote:

> Yes, it should test for xattr too,

Frankly, I suspect that the sanest way to handle that is this:
* new superblock flag - MS_NOSEC
* S_NOSEC is never set unless we have MS_NOSEC
* mount_bdev() sets it before calling fill_super callback.
* ocfs2 and fuse *clear* it in their fill_super
* btrfs manually sets it in its ->mount()
... and if gfs2 or any other non-trivial fs wants to use that, it'll need
to set MS_NOSEC in its ->mount() and take care of clearing S_NOSEC whenever
we decide it might've gone stale (a-la your patch).

That way we do not have a hole on network filesystems, get rid of duplicate
xattr / SxID checks on local block ones (which is the majority of filesystems
that might care about all that crap) and keep the patch size on saner side...

Something like this:

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 9b2e7e5..d158b67 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -819,7 +819,7 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
} else {
char b[BDEVNAME_SIZE];

- s->s_flags = flags;
+ s->s_flags = flags | MS_NOSEC;
strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
error = btrfs_fill_super(s, fs_devices, data,
flags & MS_SILENT ? 1 : 0);
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index cc6ec4b..38f84cd 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -921,6 +921,8 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
if (sb->s_flags & MS_MANDLOCK)
goto err;

+ sb->s_flags &= ~MS_NOSEC;
+
if (!parse_fuse_opt((char *) data, &d, is_bdev))
goto err;

diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
index cdbaf5e..56f6102 100644
--- a/fs/ocfs2/super.c
+++ b/fs/ocfs2/super.c
@@ -1072,7 +1072,7 @@ static int ocfs2_fill_super(struct super_block *sb, void *data, int silent)

sb->s_magic = OCFS2_SUPER_MAGIC;

- sb->s_flags = (sb->s_flags & ~MS_POSIXACL) |
+ sb->s_flags = (sb->s_flags & ~(MS_POSIXACL | MS_NOSEC)) |
((osb->s_mount_opt & OCFS2_MOUNT_POSIX_ACL) ? MS_POSIXACL : 0);

/* Hard readonly mode only if: bdev_read_only, MS_RDONLY,
diff --git a/fs/super.c b/fs/super.c
index c755939..ab3d672 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -822,7 +822,7 @@ struct dentry *mount_bdev(struct file_system_type *fs_type,
} else {
char b[BDEVNAME_SIZE];

- s->s_flags = flags;
+ s->s_flags = flags | MS_NOSEC;
s->s_mode = mode;
strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
sb_set_blocksize(s, block_size(bdev));
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c55d6b7..646a183 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -208,6 +208,7 @@ struct inodes_stat_t {
#define MS_KERNMOUNT (1<<22) /* this is a kern_mount call */
#define MS_I_VERSION (1<<23) /* Update inode I_version field */
#define MS_STRICTATIME (1<<24) /* Always perform atime updates */
+#define MS_NOSEC (1<<28)
#define MS_BORN (1<<29)
#define MS_ACTIVE (1<<30)
#define MS_NOUSER (1<<31)
@@ -2591,7 +2592,7 @@ static inline int is_sxid(mode_t mode)

static inline void inode_has_no_xattr(struct inode *inode)
{
- if (!is_sxid(inode->i_mode))
+ if (!is_sxid(inode->i_mode) && (inode->i_sb->s_flags & MS_NOSEC))
inode->i_flags |= S_NOSEC;
}

diff --git a/mm/filemap.c b/mm/filemap.c
index d7b1057..a8251a8 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2000,7 +2000,7 @@ int file_remove_suid(struct file *file)
error = security_inode_killpriv(dentry);
if (!error && killsuid)
error = __remove_suid(dentry, killsuid);
- if (!error)
+ if (!error && (inode->i_sb->s_flags & MS_NOSEC))
inode->i_flags |= S_NOSEC;

return error;