Messages in this thread Patch in this message | | | From | Andrew Lutomirski <> | Date | Tue, 20 Apr 2010 22:49:39 -0400 | Subject | [RFC] Clean up MNT_NOSUID handling in exec |
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On Tue, Apr 20, 2010 at 10:25 PM, Serge E. Hallyn <serue@us.ibm.com> wrote: > Quoting Andrew Lutomirski (luto@mit.edu): >> On Tue, Apr 20, 2010 at 8:37 AM, Stephen Smalley <sds@tycho.nsa.gov> wrote: >> > >> > At least in the case of SELinux, context transitions upon execve are >> > already disabled in the nosuid case, and Eric's patch updated the >> > SELinux test accordingly. >> >> I don't see that code in current -linus, nor do I see where SELinux >> affects dumpability. What's supposed to happen? I'm writing a patch >> right now to clean this stuff up. > > check out security/selinux/hooks.c:selinux_bprm_set_creds() > > if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) > new_tsec->sid = old_tsec->sid; > > I assume that's it?
*sigh*, that's it, of course.
But it seems odd that if you ask the system to change sid (i.e. exec_sid) and then you exec something that's nosuid, your request gets silently ignored. Presumably either the request should be respected or some error should occur.
Also, the FILE__EXECUTE_NO_TRANS check looks bogus in the nosuid case -- you can't trust security labels if nosuid.
Here's a compile-tested patch (against current -git) that might make this all it bit more sane, and as a bonus it makes it easier to reuse the NOSUID mechanism down the road for some prctl flag. Thoughts? SECINITSID_UNLABELED might want to be SECINITSID_FILE.
diff --git a/fs/exec.c b/fs/exec.c index 49cdaa1..9b34234 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1151,11 +1151,14 @@ int prepare_binprm(struct linux_binprm *bprm) if (bprm->file->f_op == NULL) return -EACCES;
+ /* Check this exactly once to avoid races. */ + bprm->file_nosuid = !!(bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID); + /* clear any previous set[ug]id data from a previous binary */ bprm->cred->euid = current_euid(); bprm->cred->egid = current_egid();
- if (!(bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)) { + if (!bprm->file_nosuid) { /* Set-uid? */ if (mode & S_ISUID) { bprm->per_clear |= PER_CLEAR_ON_SETID; diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h index c809e28..ff6be04 100644 --- a/include/linux/binfmts.h +++ b/include/linux/binfmts.h @@ -36,6 +36,8 @@ struct linux_binprm{ struct mm_struct *mm; unsigned long p; /* current top of mem */ unsigned int + file_nosuid:1, /* true if file's security state should + be ignored. */ cred_prepared:1,/* true if creds already prepared (multiple * preps happen for interpreters) */ cap_effective:1;/* true if has elevated effective capabilities, diff --git a/security/commoncap.c b/security/commoncap.c index 6166973..4836913 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -390,7 +390,7 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective) if (!file_caps_enabled) return 0;
- if (bprm->file->f_vfsmnt->mnt_flags & MNT_NOSUID) + if (bprm->file_nosuid) return 0;
dentry = dget(bprm->file->f_dentry); diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 5feecb4..762ac00 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -2100,7 +2100,7 @@ static int selinux_bprm_set_creds(struct linux_binprm *bprm) { const struct task_security_struct *old_tsec; struct task_security_struct *new_tsec; - struct inode_security_struct *isec; + u32 isid; struct common_audit_data ad; struct inode *inode = bprm->file->f_path.dentry->d_inode; int rc; @@ -2116,7 +2116,9 @@ static int selinux_bprm_set_creds(struct linux_binprm *bprm)
old_tsec = current_security(); new_tsec = bprm->cred->security; - isec = inode->i_security; + isid = ((struct inode_security_struct*)inode->i_security)->sid; + if (bprm->file_nosuid) + isid = SECINITSID_UNLABELED;
/* Default to the current task SID. */ new_tsec->sid = old_tsec->sid; @@ -2133,7 +2135,7 @@ static int selinux_bprm_set_creds(struct linux_binprm *bprm) new_tsec->exec_sid = 0; } else { /* Check for a default transition on this program. */ - rc = security_transition_sid(old_tsec->sid, isec->sid, + rc = security_transition_sid(old_tsec->sid, isid, SECCLASS_PROCESS, &new_tsec->sid); if (rc) return rc; @@ -2142,11 +2144,8 @@ static int selinux_bprm_set_creds(struct linux_binprm *bprm) COMMON_AUDIT_DATA_INIT(&ad, FS); ad.u.fs.path = bprm->file->f_path;
- if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) - new_tsec->sid = old_tsec->sid; - if (new_tsec->sid == old_tsec->sid) { - rc = avc_has_perm(old_tsec->sid, isec->sid, + rc = avc_has_perm(old_tsec->sid, isid, SECCLASS_FILE, FILE__EXECUTE_NO_TRANS, &ad); if (rc) return rc; @@ -2157,7 +2156,7 @@ static int selinux_bprm_set_creds(struct linux_binprm *bprm) if (rc) return rc;
- rc = avc_has_perm(new_tsec->sid, isec->sid, + rc = avc_has_perm(new_tsec->sid, isid, SECCLASS_FILE, FILE__ENTRYPOINT, &ad); if (rc) return rc; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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