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Ktracing kevent(2) calls with unusual arguments might leads to an

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overly large allocation requests.

When ktrace-ing io, sys_kevent() allocates memory to copy the
requested changes and reported events.  Allocations are sized by the
incoming syscall lengths arguments, which are user-controlled, and
might cause overflow in calculations or too large allocations.

Since io trace chunks are limited by ktr_geniosize, there is no sense
it even trying to satisfy unbounded allocations.  Export ktr_geniosize
and clamp the buffers sizes in advance.

PR:	217435
Reported by:	Tim Newsham <tim.newsham@nccgroup.trust>
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
This commit is contained in:
Konstantin Belousov 2017-03-12 13:48:24 +00:00
parent 2b665a98b5
commit 1e4296c919
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=315155
3 changed files with 17 additions and 5 deletions
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18
sys/kern/kern_event.c
View File

@ -887,6 +887,15 @@ kern_kqueue(struct thread *td, int flags, struct filecaps *fcaps)
return (0);
}
static size_t
kev_iovlen(int n, u_int kgio)
{
if (n < 0 || n >= kgio / sizeof(struct kevent))
return (kgio);
return (n * sizeof(struct kevent));
}
#ifndef _SYS_SYSPROTO_H_
struct kevent_args {
int fd;
@ -910,6 +919,7 @@ sys_kevent(struct thread *td, struct kevent_args *uap)
struct iovec ktriov;
struct uio *ktruioin = NULL;
struct uio *ktruioout = NULL;
u_int kgio;
#endif
if (uap->timeout != NULL) {
@ -922,13 +932,15 @@ sys_kevent(struct thread *td, struct kevent_args *uap)
#ifdef KTRACE
if (KTRPOINT(td, KTR_GENIO)) {
kgio = ktr_geniosize;
ktriov.iov_base = uap->changelist;
ktriov.iov_len = uap->nchanges * sizeof(struct kevent);
ktriov.iov_len = kev_iovlen(uap->nchanges, kgio);
ktruio = (struct uio){ .uio_iov = &ktriov, .uio_iovcnt = 1,
.uio_segflg = UIO_USERSPACE, .uio_rw = UIO_READ,
.uio_td = td };
ktruioin = cloneuio(&ktruio);
ktriov.iov_base = uap->eventlist;
ktriov.iov_len = kev_iovlen(uap->nevents, kgio);
ktriov.iov_len = uap->nevents * sizeof(struct kevent);
ktruioout = cloneuio(&ktruio);
}
@ -939,9 +951,9 @@ sys_kevent(struct thread *td, struct kevent_args *uap)
#ifdef KTRACE
if (ktruioin != NULL) {
ktruioin->uio_resid = uap->nchanges * sizeof(struct kevent);
ktruioin->uio_resid = kev_iovlen(uap->nchanges, kgio);
ktrgenio(uap->fd, UIO_WRITE, ktruioin, 0);
ktruioout->uio_resid = td->td_retval[0] * sizeof(struct kevent);
ktruioout->uio_resid = kev_iovlen(td->td_retval[0], kgio);
ktrgenio(uap->fd, UIO_READ, ktruioout, error);
}
#endif

2
sys/kern/kern_ktrace.c
View File

@ -132,7 +132,7 @@ static SYSCTL_NODE(_kern, OID_AUTO, ktrace, CTLFLAG_RD, 0, "KTRACE options");
static u_int ktr_requestpool = KTRACE_REQUEST_POOL;
TUNABLE_INT("kern.ktrace.request_pool", &ktr_requestpool);
static u_int ktr_geniosize = PAGE_SIZE;
u_int ktr_geniosize = PAGE_SIZE;
SYSCTL_UINT(_kern_ktrace, OID_AUTO, genio_size, CTLFLAG_RWTUN, &ktr_geniosize,
0, "Maximum size of genio event payload");

2
sys/sys/ktrace.h
View File

@ -276,7 +276,7 @@ void ktrcapfail(enum ktr_cap_fail_type, const cap_rights_t *,
ktrstruct("sockaddr", (s), ((struct sockaddr *)(s))->sa_len)
#define ktrstat(s) \
ktrstruct("stat", (s), sizeof(struct stat))
extern u_int ktr_geniosize;
#else
#include <sys/cdefs.h>