Re: [PATCH v1 1/2] landlock: Handle weird files

["Günther Noack" <gnoack3000@gmail.com>]

On Fri, Jan 10, 2025 at 04:39:13PM +0100, Mickaël Salaün wrote:
> A corrupted filesystem (e.g. bcachefs) might return weird files.
> Instead of throwing a warning and allowing access to such file, treat
> them as regular files.
> 
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Günther Noack <gnoack@google.com>
> Cc: Kent Overstreet <kent.overstreet@linux.dev>
> Cc: Paul Moore <paul@paul-moore.com>
> Reported-by: syzbot+34b68f850391452207df@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/r/000000000000a65b35061cffca61@google.com
> Reported-by: syzbot+360866a59e3c80510a62@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/r/67379b3f.050a0220.85a0.0001.GAE@google.com
> Reported-by: Ubisectech Sirius <bugreport@ubisectech.com>
> Closes: https://lore.kernel.org/r/c426821d-8380-46c4-a494-7008bbd7dd13.bugreport@ubisectech.com
> Fixes: cb2c7d1a1776 ("landlock: Support filesystem access-control")
> Signed-off-by: Mickaël Salaün <mic@digikod.net>
> ---
>  security/landlock/fs.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> index e31b97a9f175..7adb25150488 100644
> --- a/security/landlock/fs.c
> +++ b/security/landlock/fs.c
> @@ -937,10 +937,6 @@ static access_mask_t get_mode_access(const umode_t mode)
>  	switch (mode & S_IFMT) {
>  	case S_IFLNK:
>  		return LANDLOCK_ACCESS_FS_MAKE_SYM;
> -	case 0:
> -		/* A zero mode translates to S_IFREG. */
> -	case S_IFREG:
> -		return LANDLOCK_ACCESS_FS_MAKE_REG;
>  	case S_IFDIR:
>  		return LANDLOCK_ACCESS_FS_MAKE_DIR;
>  	case S_IFCHR:
> @@ -951,9 +947,12 @@ static access_mask_t get_mode_access(const umode_t mode)
>  		return LANDLOCK_ACCESS_FS_MAKE_FIFO;
>  	case S_IFSOCK:
>  		return LANDLOCK_ACCESS_FS_MAKE_SOCK;
> +	case S_IFREG:
> +	case 0:
> +		/* A zero mode translates to S_IFREG. */
>  	default:
> -		WARN_ON_ONCE(1);
> -		return 0;
> +		/* Treats weird files as regular files. */
> +		return LANDLOCK_ACCESS_FS_MAKE_REG;
>  	}
>  }
>  
> -- 
> 2.47.1
> 

Reviewed-by: Günther Noack <gnoack3000@gmail.com>

Makes sense to me, since this is enforcing a stronger check than before
and can only happen in the case of corruption.

I do not have a good intuition about what happens afterwards when the
file system is in such a state.  I imagine that this will usually give
an error shortly afterwards, as the opening of the file continues?  Is
that right?

–Günther