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fork: plug a use after free of the returned process

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fork1 required its callers to pass a pointer to struct proc * which would
be set to the new process (if any). procdesc and racct manipulation also
used said pointer.

However, the process could have exited prior to do_fork return and be
automatically reaped, thus making this a use-after-free.

Fix the problem by letting callers indicate whether they want the pid or
the struct proc, return the process in stopped state for the latter case.

Reviewed by:	kib
This commit is contained in:
Mateusz Guzik 2016-02-04 04:25:30 +00:00
parent 33fd9b9a2b
commit 813361c140
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=295233
4 changed files with 76 additions and 72 deletions
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2
sys/compat/cloudabi/cloudabi_proc.c
View File

@ -77,13 +77,11 @@ cloudabi_sys_proc_fork(struct thread *td,
{
struct fork_req fr;
struct filecaps fcaps = {};
struct proc *p2;
int error, fd;
cap_rights_init(&fcaps.fc_rights, CAP_FSTAT, CAP_EVENT);
bzero(&fr, sizeof(fr));
fr.fr_flags = RFFDG | RFPROC | RFPROCDESC;
fr.fr_procp = &p2;
fr.fr_pd_fd = &fd;
fr.fr_pd_fcaps = &fcaps;
error = fork1(td, &fr);

142
sys/kern/kern_fork.c
View File

@ -102,15 +102,14 @@ int
sys_fork(struct thread *td, struct fork_args *uap)
{
struct fork_req fr;
int error;
struct proc *p2;
int error, pid;
bzero(&fr, sizeof(fr));
fr.fr_flags = RFFDG | RFPROC;
fr.fr_procp = &p2;
fr.fr_pidp = &pid;
error = fork1(td, &fr);
if (error == 0) {
td->td_retval[0] = p2->p_pid;
td->td_retval[0] = pid;
td->td_retval[1] = 0;
}
return (error);
@ -123,12 +122,11 @@ sys_pdfork(td, uap)
struct pdfork_args *uap;
{
struct fork_req fr;
int error, fd;
struct proc *p2;
int error, fd, pid;
bzero(&fr, sizeof(fr));
fr.fr_flags = RFFDG | RFPROC | RFPROCDESC;
fr.fr_procp = &p2;
fr.fr_pidp = &pid;
fr.fr_pd_fd = &fd;
fr.fr_pd_flags = uap->flags;
/*
@ -138,7 +136,7 @@ sys_pdfork(td, uap)
*/
error = fork1(td, &fr);
if (error == 0) {
td->td_retval[0] = p2->p_pid;
td->td_retval[0] = pid;
td->td_retval[1] = 0;
error = copyout(&fd, uap->fdp, sizeof(fd));
}
@ -150,15 +148,14 @@ int
sys_vfork(struct thread *td, struct vfork_args *uap)
{
struct fork_req fr;
int error;
struct proc *p2;
int error, pid;
bzero(&fr, sizeof(fr));
fr.fr_flags = RFFDG | RFPROC | RFPPWAIT | RFMEM;
fr.fr_procp = &p2;
fr.fr_pidp = &pid;
error = fork1(td, &fr);
if (error == 0) {
td->td_retval[0] = p2->p_pid;
td->td_retval[0] = pid;
td->td_retval[1] = 0;
}
return (error);
@ -168,8 +165,7 @@ int
sys_rfork(struct thread *td, struct rfork_args *uap)
{
struct fork_req fr;
struct proc *p2;
int error;
int error, pid;
/* Don't allow kernel-only flags. */
if ((uap->flags & RFKERNELONLY) != 0)
@ -178,10 +174,10 @@ sys_rfork(struct thread *td, struct rfork_args *uap)
AUDIT_ARG_FFLAGS(uap->flags);
bzero(&fr, sizeof(fr));
fr.fr_flags = uap->flags;
fr.fr_procp = &p2;
fr.fr_pidp = &pid;
error = fork1(td, &fr);
if (error == 0) {
td->td_retval[0] = p2 ? p2->p_pid : 0;
td->td_retval[0] = pid;
td->td_retval[1] = 0;
}
return (error);
@ -382,11 +378,11 @@ fork_norfproc(struct thread *td, int flags)
}
static void
do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
struct vmspace *vm2, int pdflags)
do_fork(struct thread *td, struct fork_req *fr, struct proc *p2, struct thread *td2,
struct vmspace *vm2, struct file *fp_procdesc)
{
struct proc *p1, *pptr;
int p2_held, trypid;
int trypid;
struct filedesc *fd;
struct filedesc_to_leader *fdtol;
struct sigacts *newsigacts;
@ -394,10 +390,9 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
sx_assert(&proctree_lock, SX_SLOCKED);
sx_assert(&allproc_lock, SX_XLOCKED);
p2_held = 0;
p1 = td->td_proc;
trypid = fork_findpid(flags);
trypid = fork_findpid(fr->fr_flags);
sx_sunlock(&proctree_lock);
@ -430,7 +425,7 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
/*
* Malloc things while we don't hold any locks.
*/
if (flags & RFSIGSHARE)
if (fr->fr_flags & RFSIGSHARE)
newsigacts = NULL;
else
newsigacts = sigacts_alloc();
@ -438,10 +433,10 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
/*
* Copy filedesc.
*/
if (flags & RFCFDG) {
if (fr->fr_flags & RFCFDG) {
fd = fdinit(p1->p_fd, false);
fdtol = NULL;
} else if (flags & RFFDG) {
} else if (fr->fr_flags & RFFDG) {
fd = fdcopy(p1->p_fd);
fdtol = NULL;
} else {
@ -449,7 +444,7 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
if (p1->p_fdtol == NULL)
p1->p_fdtol = filedesc_to_leader_alloc(NULL, NULL,
p1->p_leader);
if ((flags & RFTHREAD) != 0) {
if ((fr->fr_flags & RFTHREAD) != 0) {
/*
* Shared file descriptor table, and shared
* process leaders.
@ -517,16 +512,16 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
vm_domain_policy_localcopy(&p2->p_vm_dom_policy,
&p1->p_vm_dom_policy);
if (flags & RFSIGSHARE) {
if (fr->fr_flags & RFSIGSHARE) {
p2->p_sigacts = sigacts_hold(p1->p_sigacts);
} else {
sigacts_copy(newsigacts, p1->p_sigacts);
p2->p_sigacts = newsigacts;
}
if (flags & RFTSIGZMB)
p2->p_sigparent = RFTSIGNUM(flags);
else if (flags & RFLINUXTHPN)
if (fr->fr_flags & RFTSIGZMB)
p2->p_sigparent = RFTSIGNUM(fr->fr_flags);
else if (fr->fr_flags & RFLINUXTHPN)
p2->p_sigparent = SIGUSR1;
else
p2->p_sigparent = SIGCHLD;
@ -559,7 +554,7 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
/*
* Set up linkage for kernel based threading.
*/
if ((flags & RFTHREAD) != 0) {
if ((fr->fr_flags & RFTHREAD) != 0) {
mtx_lock(&ppeers_lock);
p2->p_peers = p1->p_peers;
p1->p_peers = p2;
@ -606,7 +601,7 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT)
p2->p_flag |= P_CONTROLT;
SESS_UNLOCK(p1->p_session);
if (flags & RFPPWAIT)
if (fr->fr_flags & RFPPWAIT)
p2->p_flag |= P_PPWAIT;
p2->p_pgrp = p1->p_pgrp;
@ -640,7 +635,7 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
* of init. This effectively disassociates the child from the
* parent.
*/
if ((flags & RFNOWAIT) != 0) {
if ((fr->fr_flags & RFNOWAIT) != 0) {
pptr = p1->p_reaper;
p2->p_reaper = pptr;
} else {
@ -668,13 +663,13 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
* Finish creating the child process. It will return via a different
* execution path later. (ie: directly into user mode)
*/
vm_forkproc(td, p2, td2, vm2, flags);
vm_forkproc(td, p2, td2, vm2, fr->fr_flags);
if (flags == (RFFDG | RFPROC)) {
if (fr->fr_flags == (RFFDG | RFPROC)) {
PCPU_INC(cnt.v_forks);
PCPU_ADD(cnt.v_forkpages, p2->p_vmspace->vm_dsize +
p2->p_vmspace->vm_ssize);
} else if (flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
} else if (fr->fr_flags == (RFFDG | RFPROC | RFPPWAIT | RFMEM)) {
PCPU_INC(cnt.v_vforks);
PCPU_ADD(cnt.v_vforkpages, p2->p_vmspace->vm_dsize +
p2->p_vmspace->vm_ssize);
@ -693,14 +688,14 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
* can happen that might cause that process to need the descriptor.
* However, don't do this until after fork(2) can no longer fail.
*/
if (flags & RFPROCDESC)
procdesc_new(p2, pdflags);
if (fr->fr_flags & RFPROCDESC)
procdesc_new(p2, fr->fr_pd_flags);
/*
* Both processes are set up, now check if any loadable modules want
* to adjust anything.
*/
EVENTHANDLER_INVOKE(process_fork, p1, p2, flags);
EVENTHANDLER_INVOKE(process_fork, p1, p2, fr->fr_flags);
/*
* Set the child start time and mark the process as being complete.
@ -719,9 +714,14 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
* this only after p_state is PRS_NORMAL since the fasttrap module will
* use pfind() later on.
*/
if ((flags & RFMEM) == 0 && dtrace_fasttrap_fork)
if ((fr->fr_flags & RFMEM) == 0 && dtrace_fasttrap_fork)
dtrace_fasttrap_fork(p1, p2);
#endif
/*
* Hold the process so that it cannot exit after we make it runnable,
* but before we wait for the debugger.
*/
_PHOLD(p2);
if ((p1->p_flag & (P_TRACED | P_FOLLOWFORK)) == (P_TRACED |
P_FOLLOWFORK)) {
/*
@ -734,24 +734,12 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
td->td_dbgflags |= TDB_FORK;
td->td_dbg_forked = p2->p_pid;
td2->td_dbgflags |= TDB_STOPATFORK;
_PHOLD(p2);
p2_held = 1;
}
if (flags & RFPPWAIT) {
if (fr->fr_flags & RFPPWAIT) {
td->td_pflags |= TDP_RFPPWAIT;
td->td_rfppwait_p = p2;
}
PROC_UNLOCK(p2);
if ((flags & RFSTOPPED) == 0) {
/*
* If RFSTOPPED not requested, make child runnable and
* add to run queue.
*/
thread_lock(td2);
TD_SET_CAN_RUN(td2);
sched_add(td2, SRQ_BORING);
thread_unlock(td2);
}
/*
* Now can be swapped.
@ -763,16 +751,36 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
* Tell any interested parties about the new process.
*/
knote_fork(&p1->p_klist, p2->p_pid);
SDT_PROBE3(proc, , , create, p2, p1, flags);
SDT_PROBE3(proc, , , create, p2, p1, fr->fr_flags);
if (fr->fr_flags & RFPROCDESC) {
procdesc_finit(p2->p_procdesc, fp_procdesc);
fdrop(fp_procdesc, td);
}
if ((fr->fr_flags & RFSTOPPED) == 0) {
/*
* If RFSTOPPED not requested, make child runnable and
* add to run queue.
*/
thread_lock(td2);
TD_SET_CAN_RUN(td2);
sched_add(td2, SRQ_BORING);
thread_unlock(td2);
if (fr->fr_pidp != NULL)
*fr->fr_pidp = p2->p_pid;
} else {
*fr->fr_procp = p2;
}
PROC_LOCK(p2);
/*
* Wait until debugger is attached to child.
*/
PROC_LOCK(p2);
while ((td2->td_dbgflags & TDB_STOPATFORK) != 0)
cv_wait(&p2->p_dbgwait, &p2->p_mtx);
if (p2_held)
_PRELE(p2);
_PRELE(p2);
racct_proc_fork_done(p2);
PROC_UNLOCK(p2);
}
@ -792,6 +800,11 @@ fork1(struct thread *td, struct fork_req *fr)
flags = fr->fr_flags;
pages = fr->fr_pages;
if ((flags & RFSTOPPED) != 0)
MPASS(fr->fr_procp != NULL && fr->fr_pidp == NULL);
else
MPASS(fr->fr_procp == NULL);
/* Check for the undefined or unimplemented flags. */
if ((flags & ~(RFFLAGS | RFTSIGFLAGS(RFTSIGMASK))) != 0)
return (EINVAL);
@ -825,7 +838,10 @@ fork1(struct thread *td, struct fork_req *fr)
* certain parts of a process from itself.
*/
if ((flags & RFPROC) == 0) {
*fr->fr_procp = NULL;
if (fr->fr_procp != NULL)
*fr->fr_procp = NULL;
else if (fr->fr_pidp != NULL)
*fr->fr_pidp = 0;
return (fork_norfproc(td, flags));
}
@ -953,17 +969,7 @@ fork1(struct thread *td, struct fork_req *fr)
lim_cur(td, RLIMIT_NPROC));
}
if (ok) {
do_fork(td, flags, newproc, td2, vm2, fr->fr_pd_flags);
/*
* Return child proc pointer to parent.
*/
*fr->fr_procp = newproc;
if (flags & RFPROCDESC) {
procdesc_finit(newproc->p_procdesc, fp_procdesc);
fdrop(fp_procdesc, td);
}
racct_proc_fork_done(newproc);
do_fork(td, fr, newproc, td2, vm2, fp_procdesc);
return (0);
}

3
sys/kern/kern_racct.c
View File

@ -957,16 +957,15 @@ void
racct_proc_fork_done(struct proc *child)
{
PROC_LOCK_ASSERT(child, MA_OWNED);
#ifdef RCTL
if (!racct_enable)
return;
PROC_LOCK(child);
mtx_lock(&racct_lock);
rctl_enforce(child, RACCT_NPROC, 0);
rctl_enforce(child, RACCT_NTHR, 0);
mtx_unlock(&racct_lock);
PROC_UNLOCK(child);
#endif
}

1
sys/sys/proc.h
View File

@ -910,6 +910,7 @@ struct proc *zpfind(pid_t); /* Find zombie process by id. */
struct fork_req {
int fr_flags;
int fr_pages;
int *fr_pidp;
struct proc **fr_procp;
int *fr_pd_fd;
int fr_pd_flags;