Christian Brauner <christian.brauner@xxxxxxxxxx> writes: > 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. This does not handle the v3 capabilites xattr with embeds a uid. So at least at that level you are missing some critical conversions. Eric > Link: https://lore.kernel.org/r/20210112220124.837960-32-christian.brauner@xxxxxxxxxx > Cc: Christoph Hellwig <hch@xxxxxx> > Cc: David Howells <dhowells@xxxxxxxxxx> > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > Cc: linux-fsdevel@xxxxxxxxxxxxxxx > Reviewed-by: Christoph Hellwig <hch@xxxxxx> > Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx> > --- > /* v2 */ > unchanged > > /* v3 */ > unchanged > > /* v4 */ > - Serge Hallyn <serge@xxxxxxxxxx>: > - Use "mnt_userns" to refer to a vfsmount's userns everywhere to make > terminology consistent. > > /* v5 */ > unchanged > base-commit: 7c53f6b671f4aba70ff15e1b05148b10d58c2837 > > /* v6 */ > base-commit: 19c329f6808995b142b3966301f217c831e7cf31 > > - Christoph Hellwig <hch@xxxxxx>: > - Use new file_mnt_user_ns() helper. > --- > fs/exec.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/fs/exec.c b/fs/exec.c > index d803227805f6..48d1e8b1610b 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 */
