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isolation: keep CAP_SYS_PTRACE when required

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When pasta is started from an existing userns and tries to join the
netns from another process it fails to open /proc/$pid/ns/net due the
missing CAP_SYS_PTRACE capability in the --netns-only case.

A simple reproducer for this.
First create a userns:
$ unshare -r

Then create a new netns inside it and try to join that netns with pasta.
$ unshare -n sleep inf &
$ pasta --config-net --netns /proc/$!/ns/net

Signed-off-by: Paul Holzinger <pholzing@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Paul Holzinger 2023-06-23 10:25:32 +02:00 committed by Stefano Brivio
parent 5b646b9b10
commit 594dce66d3
1 changed files with 3 additions and 1 deletions
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4
isolation.c
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@ -202,9 +202,11 @@ void isolate_initial(void)
* a mapping from UID 0, which only happens with pasta spawning a child
* from a non-init user namespace (pasta can't run as root), we need to
* retain CAP_SETFCAP too.
* We also need to keep CAP_SYS_PTRACE in order to join an existing netns
* path under /proc/$pid/ns/net which was created in the same userns.
*/
if (!ns_is_init() && !geteuid())
keep |= BIT(CAP_SETFCAP);
keep |= BIT(CAP_SETFCAP) | BIT(CAP_SYS_PTRACE);
drop_caps_ep_except(keep);
}