2021-10-21 15:17:53

by Lorenz Bauer

Subject: [PATCH bpf-next v2 1/3] libfs: support RENAME_EXCHANGE in simple_rename()

Allow atomic exchange via RENAME_EXCHANGE when using simple_rename.
This affects binderfs, ramfs, hubetlbfs and bpffs. There isn't much
to do except update the various *time fields.

Signed-off-by: Lorenz Bauer <[email protected]>
---
fs/libfs.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/libfs.c b/fs/libfs.c
index 51b4de3b3447..93c03d593749 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -455,9 +455,12 @@ int simple_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
struct inode *inode = d_inode(old_dentry);
int they_are_dirs = d_is_dir(old_dentry);

- if (flags & ~RENAME_NOREPLACE)
+ if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
return -EINVAL;

+ if (flags & RENAME_EXCHANGE)
+ goto done;
+
if (!simple_empty(new_dentry))
return -ENOTEMPTY;

@@ -472,6 +475,7 @@ int simple_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
inc_nlink(new_dir);
}

+done:
old_dir->i_ctime = old_dir->i_mtime = new_dir->i_ctime =
new_dir->i_mtime = inode->i_ctime = current_time(old_dir);

--
2.32.0

2021-10-22 00:37:49

by Alexei Starovoitov

Subject: Re: [PATCH bpf-next v2 1/3] libfs: support RENAME_EXCHANGE in simple_rename()

On Thu, Oct 21, 2021 at 8:16 AM Lorenz Bauer <[email protected]> wrote:
>
> Allow atomic exchange via RENAME_EXCHANGE when using simple_rename.
> This affects binderfs, ramfs, hubetlbfs and bpffs. There isn't much
> to do except update the various *time fields.
>
> Signed-off-by: Lorenz Bauer <[email protected]>

Al,

could you please Ack this patch so we can route the whole set through
bpf-next tree?

2021-10-27 23:23:40

by Daniel Borkmann

Subject: Re: [PATCH bpf-next v2 1/3] libfs: support RENAME_EXCHANGE in simple_rename()

[ Adding Miklos & Greg to Cc for review given e0e0be8a8355 ("libfs: support RENAME_NOREPLACE in
simple_rename()"). If you have a chance, would be great if you could take a look, thanks! ]

On 10/21/21 5:15 PM, Lorenz Bauer wrote:
> Allow atomic exchange via RENAME_EXCHANGE when using simple_rename.
> This affects binderfs, ramfs, hubetlbfs and bpffs. There isn't much
> to do except update the various *time fields.
>
> Signed-off-by: Lorenz Bauer <[email protected]>
> ---
> fs/libfs.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/fs/libfs.c b/fs/libfs.c
> index 51b4de3b3447..93c03d593749 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -455,9 +455,12 @@ int simple_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
> struct inode *inode = d_inode(old_dentry);
> int they_are_dirs = d_is_dir(old_dentry);
>
> - if (flags & ~RENAME_NOREPLACE)
> + if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
> return -EINVAL;
>
> + if (flags & RENAME_EXCHANGE)
> + goto done;
> +
> if (!simple_empty(new_dentry))
> return -ENOTEMPTY;
>
> @@ -472,6 +475,7 @@ int simple_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
> inc_nlink(new_dir);
> }
>
> +done:
> old_dir->i_ctime = old_dir->i_mtime = new_dir->i_ctime =
> new_dir->i_mtime = inode->i_ctime = current_time(old_dir);
>
>

2021-10-28 08:45:03

by Miklos Szeredi

Subject: Re: [PATCH bpf-next v2 1/3] libfs: support RENAME_EXCHANGE in simple_rename()

On Thu, Oct 28, 2021 at 1:46 AM Daniel Borkmann <[email protected]> wrote:
>
> [ Adding Miklos & Greg to Cc for review given e0e0be8a8355 ("libfs: support RENAME_NOREPLACE in
> simple_rename()"). If you have a chance, would be great if you could take a look, thanks! ]
>
> On 10/21/21 5:15 PM, Lorenz Bauer wrote:
> > Allow atomic exchange via RENAME_EXCHANGE when using simple_rename.
> > This affects binderfs, ramfs, hubetlbfs and bpffs. There isn't much
> > to do except update the various *time fields.
> >
> > Signed-off-by: Lorenz Bauer <[email protected]>
> > ---
> > fs/libfs.c | 6 +++++-
> > 1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/libfs.c b/fs/libfs.c
> > index 51b4de3b3447..93c03d593749 100644
> > --- a/fs/libfs.c
> > +++ b/fs/libfs.c
> > @@ -455,9 +455,12 @@ int simple_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
> > struct inode *inode = d_inode(old_dentry);
> > int they_are_dirs = d_is_dir(old_dentry);
> >
> > - if (flags & ~RENAME_NOREPLACE)
> > + if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
> > return -EINVAL;
> >
> > + if (flags & RENAME_EXCHANGE)
> > + goto done;
> > +

This is not sufficient. RENAME_EXCHANGE can swap a dir and a
non-dir, in which case the parent nlink counters need to be fixed up.

See shmem_exchange(). My suggestion is to move that function to
libfs.c:simple_rename_exchange().

Thanks,
Miklos

2021-10-28 09:52:31

by Lorenz Bauer

Subject: Re: [PATCH bpf-next v2 1/3] libfs: support RENAME_EXCHANGE in simple_rename()

On Thu, 28 Oct 2021 at 09:43, Miklos Szeredi <[email protected]> wrote:
>
> This is not sufficient. RENAME_EXCHANGE can swap a dir and a
> non-dir, in which case the parent nlink counters need to be fixed up.
>
> See shmem_exchange(). My suggestion is to move that function to
> libfs.c:simple_rename_exchange().

Thanks for the pointer, I sent a v3.

Lorenz

--
Lorenz Bauer | Systems Engineer
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