exec: Add credential change information into imgp for process_exec hook.
This allows an EVENTHANDLER(process_exec) hook to see if the new image will cause credentials to change whether due to setgid/setuid or because of POSIX saved-id semantics. This adds 3 new fields into image_params: struct ucred *newcred Non-null if the credentials will change. bool credential_setid True if the new image is setuid or setgid. This will pre-determine the new credentials before invoking the image activators, where the process_exec hook is called. The new credentials will be installed into the process in the same place as before, after image activators are done handling the image. MFC after: 2 weeks Reviewed by: kib Sponsored by: EMC / Isilon Storage Division Differential Revision: https://reviews.freebsd.org/D6544
This commit is contained in:
Bryan Drewery
parent
8f7ada2196
commit
881010f05d
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=300792
@ -356,7 +356,7 @@ do_execve(td, args, mac_p)
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{
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struct proc *p = td->td_proc;
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struct nameidata nd;
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struct ucred *newcred = NULL, *oldcred;
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struct ucred *oldcred;
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struct uidinfo *euip = NULL;
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register_t *stack_base;
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int error, i;
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@ -404,6 +404,7 @@ do_execve(td, args, mac_p)
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imgp->proc = p;
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imgp->attr = &attr;
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imgp->args = args;
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oldcred = p->p_ucred;
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#ifdef MAC
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error = mac_execve_enter(imgp, mac_p);
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@ -485,6 +486,87 @@ do_execve(td, args, mac_p)
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goto exec_fail_dealloc;
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imgp->proc->p_osrel = 0;
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/*
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* Implement image setuid/setgid.
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*
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* Determine new credentials before attempting image activators
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* so that it can be used by process_exec handlers to determine
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* credential/setid changes.
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*
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* Don't honor setuid/setgid if the filesystem prohibits it or if
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* the process is being traced.
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*
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* We disable setuid/setgid/etc in capability mode on the basis
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* that most setugid applications are not written with that
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* environment in mind, and will therefore almost certainly operate
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* incorrectly. In principle there's no reason that setugid
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* applications might not be useful in capability mode, so we may want
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* to reconsider this conservative design choice in the future.
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*
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* XXXMAC: For the time being, use NOSUID to also prohibit
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* transitions on the file system.
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*/
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credential_changing = 0;
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credential_changing |= (attr.va_mode & S_ISUID) &&
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oldcred->cr_uid != attr.va_uid;
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credential_changing |= (attr.va_mode & S_ISGID) &&
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oldcred->cr_gid != attr.va_gid;
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#ifdef MAC
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will_transition = mac_vnode_execve_will_transition(oldcred, imgp->vp,
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interpvplabel, imgp);
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credential_changing |= will_transition;
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#endif
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if (credential_changing &&
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#ifdef CAPABILITY_MODE
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((oldcred->cr_flags & CRED_FLAG_CAPMODE) == 0) &&
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#endif
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(imgp->vp->v_mount->mnt_flag & MNT_NOSUID) == 0 &&
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(p->p_flag & P_TRACED) == 0) {
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imgp->credential_setid = true;
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VOP_UNLOCK(imgp->vp, 0);
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imgp->newcred = crdup(oldcred);
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if (attr.va_mode & S_ISUID) {
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euip = uifind(attr.va_uid);
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change_euid(imgp->newcred, euip);
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}
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vn_lock(imgp->vp, LK_EXCLUSIVE | LK_RETRY);
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if (attr.va_mode & S_ISGID)
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change_egid(imgp->newcred, attr.va_gid);
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/*
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* Implement correct POSIX saved-id behavior.
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*
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* XXXMAC: Note that the current logic will save the
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* uid and gid if a MAC domain transition occurs, even
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* though maybe it shouldn't.
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*/
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change_svuid(imgp->newcred, imgp->newcred->cr_uid);
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change_svgid(imgp->newcred, imgp->newcred->cr_gid);
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} else {
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/*
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* Implement correct POSIX saved-id behavior.
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*
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* XXX: It's not clear that the existing behavior is
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* POSIX-compliant. A number of sources indicate that the
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* saved uid/gid should only be updated if the new ruid is
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* not equal to the old ruid, or the new euid is not equal
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* to the old euid and the new euid is not equal to the old
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* ruid. The FreeBSD code always updates the saved uid/gid.
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* Also, this code uses the new (replaced) euid and egid as
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* the source, which may or may not be the right ones to use.
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*/
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if (oldcred->cr_svuid != oldcred->cr_uid ||
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oldcred->cr_svgid != oldcred->cr_gid) {
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VOP_UNLOCK(imgp->vp, 0);
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imgp->newcred = crdup(oldcred);
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vn_lock(imgp->vp, LK_EXCLUSIVE | LK_RETRY);
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change_svuid(imgp->newcred, imgp->newcred->cr_uid);
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change_svgid(imgp->newcred, imgp->newcred->cr_gid);
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}
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}
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/* The new credentials are installed into the process later. */
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/*
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* If the current process has a special image activator it
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* wants to try first, call it. For example, emulating shell
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@ -542,6 +624,11 @@ do_execve(td, args, mac_p)
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vput(newtextvp);
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vm_object_deallocate(imgp->object);
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imgp->object = NULL;
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imgp->credential_setid = false;
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if (imgp->newcred != NULL) {
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crfree(imgp->newcred);
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imgp->newcred = NULL;
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}
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/* set new name to that of the interpreter */
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NDINIT(&nd, LOOKUP, LOCKLEAF | FOLLOW | SAVENAME,
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UIO_SYSSPACE, imgp->interpreter_name, td);
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@ -639,7 +726,6 @@ do_execve(td, args, mac_p)
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PROC_LOCK(p);
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if (oldsigacts)
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p->p_sigacts = newsigacts;
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oldcred = p->p_ucred;
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/* Stop profiling */
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stopprofclock(p);
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@ -671,38 +757,9 @@ do_execve(td, args, mac_p)
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}
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/*
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* Implement image setuid/setgid.
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*
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* Don't honor setuid/setgid if the filesystem prohibits it or if
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* the process is being traced.
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*
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* We disable setuid/setgid/etc in capability mode on the basis
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* that most setugid applications are not written with that
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* environment in mind, and will therefore almost certainly operate
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* incorrectly. In principle there's no reason that setugid
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* applications might not be useful in capability mode, so we may want
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* to reconsider this conservative design choice in the future.
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*
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* XXXMAC: For the time being, use NOSUID to also prohibit
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* transitions on the file system.
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* Implement image setuid/setgid installation.
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*/
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credential_changing = 0;
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credential_changing |= (attr.va_mode & S_ISUID) && oldcred->cr_uid !=
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attr.va_uid;
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credential_changing |= (attr.va_mode & S_ISGID) && oldcred->cr_gid !=
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attr.va_gid;
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#ifdef MAC
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will_transition = mac_vnode_execve_will_transition(oldcred, imgp->vp,
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interpvplabel, imgp);
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credential_changing |= will_transition;
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#endif
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if (credential_changing &&
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#ifdef CAPABILITY_MODE
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((oldcred->cr_flags & CRED_FLAG_CAPMODE) == 0) &&
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#endif
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(imgp->vp->v_mount->mnt_flag & MNT_NOSUID) == 0 &&
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(p->p_flag & P_TRACED) == 0) {
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if (imgp->credential_setid) {
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/*
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* Turn off syscall tracing for set-id programs, except for
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* root. Record any set-id flags first to make sure that
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@ -728,61 +785,24 @@ do_execve(td, args, mac_p)
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error = fdcheckstd(td);
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if (error != 0)
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goto done1;
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newcred = crdup(oldcred);
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euip = uifind(attr.va_uid);
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vn_lock(imgp->vp, LK_SHARED | LK_RETRY);
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PROC_LOCK(p);
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/*
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* Set the new credentials.
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*/
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if (attr.va_mode & S_ISUID)
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change_euid(newcred, euip);
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if (attr.va_mode & S_ISGID)
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change_egid(newcred, attr.va_gid);
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#ifdef MAC
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if (will_transition) {
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mac_vnode_execve_transition(oldcred, newcred, imgp->vp,
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interpvplabel, imgp);
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mac_vnode_execve_transition(oldcred, imgp->newcred,
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imgp->vp, interpvplabel, imgp);
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}
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#endif
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/*
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* Implement correct POSIX saved-id behavior.
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*
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* XXXMAC: Note that the current logic will save the
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* uid and gid if a MAC domain transition occurs, even
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* though maybe it shouldn't.
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*/
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change_svuid(newcred, newcred->cr_uid);
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change_svgid(newcred, newcred->cr_gid);
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proc_set_cred(p, newcred);
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} else {
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if (oldcred->cr_uid == oldcred->cr_ruid &&
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oldcred->cr_gid == oldcred->cr_rgid)
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p->p_flag &= ~P_SUGID;
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/*
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* Implement correct POSIX saved-id behavior.
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*
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* XXX: It's not clear that the existing behavior is
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* POSIX-compliant. A number of sources indicate that the
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* saved uid/gid should only be updated if the new ruid is
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* not equal to the old ruid, or the new euid is not equal
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* to the old euid and the new euid is not equal to the old
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* ruid. The FreeBSD code always updates the saved uid/gid.
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* Also, this code uses the new (replaced) euid and egid as
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* the source, which may or may not be the right ones to use.
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*/
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if (oldcred->cr_svuid != oldcred->cr_uid ||
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oldcred->cr_svgid != oldcred->cr_gid) {
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PROC_UNLOCK(p);
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VOP_UNLOCK(imgp->vp, 0);
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newcred = crdup(oldcred);
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vn_lock(imgp->vp, LK_SHARED | LK_RETRY);
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PROC_LOCK(p);
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change_svuid(newcred, newcred->cr_uid);
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change_svgid(newcred, newcred->cr_gid);
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proc_set_cred(p, newcred);
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}
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}
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/*
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* Set the new credentials.
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*/
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if (imgp->newcred != NULL)
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proc_set_cred(p, imgp->newcred);
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/*
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* Store the vp for use in procfs. This vnode was referenced by namei
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@ -855,14 +875,6 @@ do_execve(td, args, mac_p)
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VOP_UNLOCK(imgp->vp, 0);
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done1:
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/*
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* Free any resources malloc'd earlier that we didn't use.
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*/
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if (euip != NULL)
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uifree(euip);
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if (newcred != NULL)
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crfree(oldcred);
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/*
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* Handle deferred decrement of ref counts.
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*/
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@ -881,10 +893,12 @@ do_execve(td, args, mac_p)
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sigacts_free(oldsigacts);
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exec_fail_dealloc:
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/*
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* free various allocated resources
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*/
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if (euip != NULL)
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uifree(euip);
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if (imgp->firstpage != NULL)
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exec_unmap_first_page(imgp);
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@ -926,6 +940,8 @@ do_execve(td, args, mac_p)
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SDT_PROBE1(proc, , , exec__failure, error);
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done2:
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if (imgp->newcred != NULL)
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crfree(oldcred);
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#ifdef MAC
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mac_execve_exit(imgp);
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mac_execve_interpreter_exit(interpvplabel);
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@ -38,6 +38,8 @@
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#define MAXSHELLCMDLEN PAGE_SIZE
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struct ucred;
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struct image_args {
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char *buf; /* pointer to string buffer */
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char *begin_argv; /* beginning of argv in buf */
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@ -82,6 +84,8 @@ struct image_params {
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int pagesizeslen;
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vm_prot_t stack_prot;
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u_long stack_sz;
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struct ucred *newcred; /* new credentials if changing */
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bool credential_setid; /* true if becoming setid */
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};
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#ifdef _KERNEL
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