Ivan Vilata i Balaguer (2019-11-01 11:10:02 -0400) wrote:
> Ludovic Courtès (2019-11-01 15:26:27 +0100) wrote:
>
> > […] What about a read-only bind mount like this:
> >
> > unshare -mUr mount --bind -o ro /var/run/nscd /tmp/tt
> >
> > ?
>
> This one looks more interesting:
>
> $ unshare -mUr mount --bind -o ro /var/run/nscd /tmp/tt && echo ok
> mount: /tmp/tt: filesystem was mounted, but any subsequent operation
> failed: Unknown error 5005.
> $ echo $?
> 32
BTW, I ran that under strace and it looks like the read-only remount fails
after mounting `/var/run/nscd` in the new namespace has succeeded:
$ strace -f unshare -mUr mount --bind -o ro /var/run/nscd /tmp/tt
[…]
access("/run/mount", R_OK|W_OK) = -1 EACCES (Permission denied)
mount("/run/nscd", "/tmp/tt", 0x14c25b0, MS_RDONLY|MS_BIND, NULL) = 0
mount("none", "/tmp/tt", NULL, MS_RDONLY|MS_REMOUNT|MS_BIND, NULL) = -1
EPERM (Operation not permitted)
write(2, "mount: ", 7mount: ) = 7
write(2, "/tmp/tt: filesystem was mounted,"..., 89/tmp/tt: filesystem was
mounted, but any subsequent operation failed: Unknown error 5005.) = 89
write(2, "\n", 1
[…]
Cheers!
--
Ivan Vilata i Balaguer -- https://elvil.net/
