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new helper: do_new_mount_fc()

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Create an fs_context-aware version of do_new_mount().  This takes an
fs_context with a superblock already attached to it.

Make do_new_mount() use do_new_mount_fc() rather than do_new_mount(); this
allows the consolidation of the mount creation, check and add steps.

To make this work, mount_too_revealing() is changed to take a superblock
rather than a mount (which the fs_context doesn't have available), allowing
this check to be done before the mount object is created.

Signed-off-by: David Howells <dhowells@redhat.com>
Co-developed-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
David Howells 2018-11-04 07:43:08 -05:00 committed by Al Viro
parent a0c9a8b8fd
commit 132e460848
1 changed files with 39 additions and 26 deletions
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65
fs/namespace.c
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@ -2523,7 +2523,37 @@ unlock:
return err;
}
static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags);
static bool mount_too_revealing(const struct super_block *sb, int *new_mnt_flags);
/*
* Create a new mount using a superblock configuration and request it
* be added to the namespace tree.
*/
static int do_new_mount_fc(struct fs_context *fc, struct path *mountpoint,
unsigned int mnt_flags)
{
struct vfsmount *mnt;
struct super_block *sb = fc->root->d_sb;
int error;
if (mount_too_revealing(sb, &mnt_flags)) {
dput(fc->root);
fc->root = NULL;
deactivate_locked_super(sb);
return -EPERM;
}
up_write(&sb->s_umount);
mnt = vfs_create_mount(fc);
if (IS_ERR(mnt))
return PTR_ERR(mnt);
error = do_add_mount(real_mount(mnt), mountpoint, mnt_flags);
if (error < 0)
mntput(mnt);
return error;
}
/*
* create a new mount for userspace and request it to be added into the
@ -2533,7 +2563,6 @@ static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
int mnt_flags, const char *name, void *data)
{
struct file_system_type *type;
struct vfsmount *mnt;
struct fs_context *fc;
const char *subtype = NULL;
int err = 0;
@ -2577,26 +2606,9 @@ static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
err = parse_monolithic_mount_data(fc, data);
if (!err)
err = vfs_get_tree(fc);
if (err)
goto out;
if (!err)
err = do_new_mount_fc(fc, path, mnt_flags);
up_write(&fc->root->d_sb->s_umount);
mnt = vfs_create_mount(fc);
if (IS_ERR(mnt)) {
err = PTR_ERR(mnt);
goto out;
}
if (mount_too_revealing(mnt, &mnt_flags)) {
mntput(mnt);
err = -EPERM;
goto out;
}
err = do_add_mount(real_mount(mnt), path, mnt_flags);
if (err)
mntput(mnt);
out:
put_fs_context(fc);
return err;
}
@ -3421,7 +3433,8 @@ bool current_chrooted(void)
return chrooted;
}
static bool mnt_already_visible(struct mnt_namespace *ns, struct vfsmount *new,
static bool mnt_already_visible(struct mnt_namespace *ns,
const struct super_block *sb,
int *new_mnt_flags)
{
int new_flags = *new_mnt_flags;
@ -3433,7 +3446,7 @@ static bool mnt_already_visible(struct mnt_namespace *ns, struct vfsmount *new,
struct mount *child;
int mnt_flags;
if (mnt->mnt.mnt_sb->s_type != new->mnt_sb->s_type)
if (mnt->mnt.mnt_sb->s_type != sb->s_type)
continue;
/* This mount is not fully visible if it's root directory
@ -3484,7 +3497,7 @@ found:
return visible;
}
static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)
static bool mount_too_revealing(const struct super_block *sb, int *new_mnt_flags)
{
const unsigned long required_iflags = SB_I_NOEXEC | SB_I_NODEV;
struct mnt_namespace *ns = current->nsproxy->mnt_ns;
@ -3494,7 +3507,7 @@ static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)
return false;
/* Can this filesystem be too revealing? */
s_iflags = mnt->mnt_sb->s_iflags;
s_iflags = sb->s_iflags;
if (!(s_iflags & SB_I_USERNS_VISIBLE))
return false;
@ -3504,7 +3517,7 @@ static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)
return true;
}
return !mnt_already_visible(ns, mnt, new_mnt_flags);
return !mnt_already_visible(ns, sb, new_mnt_flags);
}
bool mnt_may_suid(struct vfsmount *mnt)