On 17/10/2018 16:45, David Howells wrote:
Alan Jenkins <alan.christopher.jenkins@xxxxxxxxx> wrote:
I agree. I'm happy to see this is using the same check as do_remount().
* change filesystem flags. dir should be a physical root of filesystem.
* If you've mounted a non-root directory somewhere and want to do remount
* on it - tough luck.
*/
Are you suggesting that it should only work at the ultimate root of a
superblock and not a bind mount somewhere within?
That's tricky to make work for NFS because s_root is a dummy dentry.
David
Retro-actively: I do not suggest that.
I tried to answer this question in my reply to Eric correcting me. Eric
was right to correct me. I now understand the comment above
do_remount() is incorrect. I re-reviewed your diff in light of that. I
re-endorse your diff as a way to solve the problem I raised.
(I think it would be useful to remove the misleading comment above
do_remount(), to avoid future confusion.)
> @@ -186,6 +186,10 @@ SYSCALL_DEFINE3(fspick, int, dfd, const char
__user *, path, unsigned int, flags
if (ret < 0)
goto err;
+ ret = -EINVAL;
+ if (target.mnt->mnt_root != target.dentry)
+ goto err_path;
+
( the "if" statement it adds to fspick() is equivalent to the second
"if" statement in do_remount(): )
static int do_remount <https://elixir.bootlin.com/linux/v4.18/ident/do_remount>(struct path <https://elixir.bootlin.com/linux/v4.18/ident/path> *path <https://elixir.bootlin.com/linux/v4.18/ident/path>, int ms_flags, int sb_flags,
int mnt_flags, void *data)
{
int err;
struct super_block <https://elixir.bootlin.com/linux/v4.18/ident/super_block> *sb = path <https://elixir.bootlin.com/linux/v4.18/ident/path>->mnt
<https://elixir.bootlin.com/linux/v4.18/ident/mnt>->mnt_sb;
struct mount <https://elixir.bootlin.com/linux/v4.18/ident/mount> *mnt <https://elixir.bootlin.com/linux/v4.18/ident/mnt> = real_mount
<https://elixir.bootlin.com/linux/v4.18/ident/real_mount>(path
<https://elixir.bootlin.com/linux/v4.18/ident/path>->mnt
<https://elixir.bootlin.com/linux/v4.18/ident/mnt>);
if (!check_mnt <https://elixir.bootlin.com/linux/v4.18/ident/check_mnt>(mnt
<https://elixir.bootlin.com/linux/v4.18/ident/mnt>))
return -EINVAL <https://elixir.bootlin.com/linux/v4.18/ident/EINVAL>;
if (path <https://elixir.bootlin.com/linux/v4.18/ident/path>->dentry != path <https://elixir.bootlin.com/linux/v4.18/ident/path>->mnt
<https://elixir.bootlin.com/linux/v4.18/ident/mnt>->mnt_root)
return -EINVAL <https://elixir.bootlin.com/linux/v4.18/ident/EINVAL>;
Thanks
Alan
