Chroot can easily be used to subvert setuid programs. If no_new_privs,
then setuid programs don't gain any privilege, so allow chroot.
Because chroot is an easy way to break out of chroot jail, CAP_SYS_ADMIN
is still required if the caller is already chrooted.
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
---
fs/open.c | 16 ++++++++++++++--
1 files changed, 14 insertions(+), 2 deletions(-)
diff --git a/fs/open.c b/fs/open.c
index f711921..80ca7e2 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -422,6 +422,8 @@ SYSCALL_DEFINE1(chroot, const char __user *, filename)
{
struct path path;
int error;
+ struct fs_struct *fs = current->fs;
+ bool is_chrooted;
error = user_path_dir(filename, &path);
if (error)
@@ -432,13 +434,23 @@ SYSCALL_DEFINE1(chroot, const char __user *, filename)
goto dput_and_out;
error = -EPERM;
- if (!capable(CAP_SYS_CHROOT))
+ /*
+ * Chroot is dangerous unless no_new_privs is set. But we also
+ * don't want to allow unprivileged users to break out of chroot
+ * jail with another chroot call, so we require either CAP_SYS_CHROOT
+ * unless we're not chrooted already and we have no_new_privs.
+ */
+ is_chrooted = (fs->root.mnt->mnt_mountpoint !=
+ fs->root.mnt->mnt_parent->mnt_root ||
+ fs->root.dentry != fs->root.mnt->mnt_root);
+ if (!(current->no_new_privs && !is_chrooted) &&
+ !capable(CAP_SYS_CHROOT))
goto dput_and_out;
error = security_path_chroot(&path);
if (error)
goto dput_and_out;
- set_fs_root(current->fs, &path);
+ set_fs_root(fs, &path);
error = 0;
dput_and_out:
path_put(&path);
--
1.7.7.5
--
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