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passt: Accurate error reporting for sandbox()

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It's actually quite easy to make it fail depending on the
environment, accurately report errors here.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio 2022-03-27 21:55:29 +02:00
parent 33fc2dece2
commit 052424d7f5
1 changed files with 28 additions and 12 deletions
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40
passt.c
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@ -241,8 +241,6 @@ static int sandbox(struct ctx *c)
{
int flags = CLONE_NEWIPC | CLONE_NEWNS | CLONE_NEWUTS;
errno = 0;
if (!c->netns_only) {
if (c->pasta_userns_fd == -1)
flags |= CLONE_NEWUSER;
@ -259,19 +257,37 @@ static int sandbox(struct ctx *c)
if (!c->foreground || c->mode == MODE_PASST)
flags |= CLONE_NEWPID;
unshare(flags);
mount("", "/", "", MS_UNBINDABLE | MS_REC, NULL);
mount("", TMPDIR, "tmpfs", MS_NODEV | MS_NOEXEC | MS_NOSUID | MS_RDONLY,
"nr_inodes=2,nr_blocks=0");
if (chdir(TMPDIR))
if (unshare(flags)) {
perror("unshare");
return -errno;
}
syscall(SYS_pivot_root, ".", ".");
umount2(".", MNT_DETACH | UMOUNT_NOFOLLOW);
if (errno)
if (mount("", "/", "", MS_UNBINDABLE | MS_REC, NULL)) {
perror("mount /");
return -errno;
}
if (mount("", TMPDIR, "tmpfs",
MS_NODEV | MS_NOEXEC | MS_NOSUID | MS_RDONLY,
"nr_inodes=2,nr_blocks=0")) {
perror("mount tmpfs");
return -errno;
}
if (chdir(TMPDIR)) {
perror("chdir");
return -errno;
}
if (syscall(SYS_pivot_root, ".", ".")) {
perror("pivot_root");
return -errno;
}
if (umount2(".", MNT_DETACH | UMOUNT_NOFOLLOW)) {
perror("umount2");
return -errno;
}
drop_caps(); /* Relative to the new user namespace this time. */