Unverified Commit 1ab29965 authored by Christian Brauner's avatar Christian Brauner
Browse files

exec: handle idmapped mounts 

When executing a setuid binary the kernel will verify in bprm_fill_uid()
that the inode has a mapping in the caller's user namespace before
setting the callers uid and gid. Let bprm_fill_uid() handle idmapped
mounts. If the inode is accessed through an idmapped mount it is mapped
according to the mount's user namespace. Afterwards the checks are
identical to non-idmapped mounts. If the initial user namespace is
passed nothing changes so non-idmapped mounts will see identical
behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-24-christian.brauner@ubuntu.com


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
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarJames Morris <jamorris@linux.microsoft.com>
Signed-off-by: default avatarChristian Brauner <christian.brauner@ubuntu.com>
parent 435ac621

fs/exec.c

+5 −2
Original line number Diff line number Diff line
@@ -1580,6 +1580,7 @@ static void check_unsafe_exec(struct linux_binprm *bprm) 
static void bprm_fill_uid(struct linux_binprm *bprm, struct file *file)

{

	/* Handle suid and sgid on files */

	struct user_namespace *mnt_userns;

	struct inode *inode;

	unsigned int mode;

	kuid_t uid;
@@ -1596,13 +1597,15 @@ static void bprm_fill_uid(struct linux_binprm *bprm, struct file *file) 
	if (!(mode & (S_ISUID|S_ISGID)))

		return;



	mnt_userns = file_mnt_user_ns(file);



	/* Be careful if suid/sgid is set */

	inode_lock(inode);



	/* reload atomically mode/uid/gid now that lock held */

	mode = inode->i_mode;

	uid = inode->i_uid;

	gid = inode->i_gid;

	uid = i_uid_into_mnt(mnt_userns, inode);

	gid = i_gid_into_mnt(mnt_userns, inode);

	inode_unlock(inode);



	/* We ignore suid/sgid if there are no mappings for them in the ns */