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: Christoph Hellwig <hch@lst.de>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
diff --git a/fs/exec.c b/fs/exec.c
index d803227..48d1e8b 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -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 */
