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From:   Christian Brauner <christian.brauner@ubuntu.com>
To:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>,
        linux-fsdevel@vger.kernel.org
Cc:     John Johansen <john.johansen@canonical.com>,
        James Morris <jmorris@namei.org>,
        Mimi Zohar <zohar@linux.ibm.com>,
        Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
        Stephen Smalley <stephen.smalley.work@gmail.com>,
        Casey Schaufler <casey@schaufler-ca.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
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        Mrunal Patel <mpatel@redhat.com>,
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        Lennart Poettering <lennart@poettering.net>,
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        Phil Estes <estesp@gmail.com>, Serge Hallyn <serge@hallyn.com>,
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        containers@lists.linux-foundation.org,
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        linux-integrity@vger.kernel.org, selinux@vger.kernel.org,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Christoph Hellwig <hch@lst.de>
Subject: [PATCH v5 30/42] would_dump: handle idmapped mounts
Date:   Tue, 12 Jan 2021 23:01:12 +0100
Message-Id: <20210112220124.837960-31-christian.brauner@ubuntu.com>
In-Reply-To: <20210112220124.837960-1-christian.brauner@ubuntu.com>
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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