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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>,
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        Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
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        Arnd Bergmann <arnd@arndb.de>,
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        OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
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        linux-ext4@vger.kernel.org, linux-audit@redhat.com,
        linux-integrity@vger.kernel.org, selinux@vger.kernel.org,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Christoph Hellwig <hch@lst.de>
Subject: [PATCH v2 27/39] would_dump: handle idmapped mounts
Date:   Sun, 15 Nov 2020 11:37:06 +0100
Message-Id: <20201115103718.298186-28-christian.brauner@ubuntu.com>
In-Reply-To: <20201115103718.298186-1-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.

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
---
 fs/exec.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index b499a1a03934..10c06fdf78a7 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1391,14 +1391,15 @@ 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 *ns = mnt_user_ns(file->f_path.mnt);
+	if (inode_permission(ns, 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, ns, inode))
 			user_ns = user_ns->parent;
 
 		if (old != user_ns) {
-- 
2.29.2