[PATCH v3 28/38] exec: handle idmapped mounts
From: Christian Brauner <hidden>
Date: 2020-11-28 22:13:01
Also in:
fstests, linux-api, linux-ext4, linux-fsdevel, linux-security-module, selinux
Subsystem:
exec & binfmt api, elf, filesystems (vfs and infrastructure), the rest · Maintainers:
Kees Cook, Alexander Viro, Christian Brauner, Linus Torvalds
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. 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 <redacted> --- /* v2 */ unchanged /* v3 */ unchanged --- fs/exec.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index 10c06fdf78a7..7d6d3dd17e84 100644
--- a/fs/exec.c
+++ b/fs/exec.c@@ -1567,6 +1567,7 @@ 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 *user_ns; struct inode *inode; unsigned int mode; kuid_t uid;
@@ -1583,13 +1584,15 @@ static void bprm_fill_uid(struct linux_binprm *bprm, struct file *file) if (!(mode & (S_ISUID|S_ISGID))) return; + user_ns = mnt_user_ns(file->f_path.mnt); + /* 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(user_ns, inode); + gid = i_gid_into_mnt(user_ns, inode); inode_unlock(inode); /* We ignore suid/sgid if there are no mappings for them in the ns */
--
2.29.2