[PATCH v5 30/42] would_dump: handle idmapped mounts

Christian Brauner
2021-01-12T22:13:24Z

When determining whether or not to create a coredump the vfs will verify
that the caller is privileged over the inode. Make the would_dump()
helper handle idmapped mounts by passing down the mount's user namespace
of the exec file. If the initial user namespace is passed nothing
changes so non-idmapped mounts will see identical behavior as before.

Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
/* v2 */
unchanged

/* v3 */
unchanged

/* v4 */
- Serge Hallyn <serge@hallyn.com>:
- Use "mnt_userns" to refer to a vfsmount's userns everywhere to make
terminology consistent.

/* v5 */
base-commit: 7c53f6b671f4aba70ff15e1b05148b10d58c2837

- Christoph Hellwig <hch@lst.de>:
- Use new file_userns_helper().
---
fs/exec.c | 5 +++--
fs/fcntl.c | 2 +-
2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 049a8d2669db..36a1b927a8ae 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1404,14 +1404,15 @@ EXPORT_SYMBOL(begin_new_exec);
void would_dump(struct linux_binprm *bprm, struct file *file)
{
struct inode *inode = file_inode(file);
- if (inode_permission(&init_user_ns, inode, MAY_READ) < 0) {
+ struct user_namespace *mnt_userns = file_user_ns(file);
+ if (inode_permission(mnt_userns, inode, MAY_READ) < 0) {
struct user_namespace *old, *user_ns;
bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;

/* Ensure mm->user_ns contains the executable */
user_ns = old = bprm->mm->user_ns;
while ((user_ns != &init_user_ns) &&
- !privileged_wrt_inode_uidgid(user_ns, &init_user_ns, inode))
+ !privileged_wrt_inode_uidgid(user_ns, mnt_userns, inode))
user_ns = user_ns->parent;

if (old != user_ns) {
diff --git a/fs/fcntl.c b/fs/fcntl.c
index 58706031e603..ebbe831d5736 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -47,7 +47,7 @@ static int setfl(int fd, struct file * filp, unsigned long arg)

/* O_NOATIME can only be set by the owner or superuser */
if ((arg & O_NOATIME) && !(filp->f_flags & O_NOATIME))
- if (!inode_owner_or_capable(mnt_user_ns(filp->f_path.mnt), inode))
+ if (!inode_owner_or_capable(file_user_ns(filp), inode))
return -EPERM;

/* required for strict SunOS emulation */
--
2.30.0