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all: convenience api for checking overflow

we were using emalloc and erealloc to allocate
or grow arrays, often without checking for
overflow. This code adds a check for overflow,
using a uvlong and capping to 2 gigabytes of
array -- which ought to be enough for our uses.

If bigger arrays end up needed, we can tweak
the overflow checks in one place.

--- a/delta.c

+++ b/delta.c

@@ -36,7 +36,7 @@

 		db = dt->b;

 		dt->sz *= 2;

 		dt->nb = 0;

-		dt->b = emalloc(dt->sz * sizeof(Dblock));

+		dt->b = eamalloc(dt->sz, sizeof(Dblock));

 		for(i = 0; i < sz; i++)

 			if(db[i].buf != nil)

 				addblk(dt, db[i].buf, db[i].len, db[i].off, db[i].rhash);

@@ -112,7 +112,7 @@

 	rh = 0;

 	dt->nb = 0;

 	dt->sz = 128;

-	dt->b = emalloc(dt->sz*sizeof(Dblock));

+	dt->b = eamalloc(dt->sz, sizeof(Dblock));

 	while(e != bp + nbase){

 		e += nextblk(s, bp + nbase, &rh);

 		addblk(dt, s, e - s, s - bp, rh);

--- a/fetch.c

+++ b/fetch.c

@@ -175,8 +175,8 @@

 	nref = 0;

 	refsz = 16;

 	first = 1;

-	have = emalloc(refsz * sizeof(have[0]));

-	want = emalloc(refsz * sizeof(want[0]));

+	have = eamalloc(refsz, sizeof(have[0]));

+	want = eamalloc(refsz, sizeof(want[0]));

 	while(1){

 		n = readpkt(c, buf, sizeof(buf));

 		if(n == -1)

--- a/fs.c

+++ b/fs.c

@@ -669,7 +669,7 @@

 	oaux = o->aux;

 	aux = emalloc(sizeof(Gitaux));

 	aux->ncrumb = oaux->ncrumb;

-	aux->crumb = emalloc(oaux->ncrumb * sizeof(Crumb));

+	aux->crumb = eamalloc(oaux->ncrumb, sizeof(Crumb));

 	for(i = 0; i < aux->ncrumb; i++){

 		aux->crumb[i] = oaux->crumb[i];

 		aux->crumb[i].name = estrdup(oaux->crumb[i].name);

--- a/git.h

+++ b/git.h

@@ -269,7 +269,9 @@

 /* util functions */

 void	dprint(int, char *, ...);

+void	*eamalloc(ulong, ulong);

 void	*emalloc(ulong);

+void	*earealloc(void *, ulong, ulong);

 void	*erealloc(void *, ulong);

 char	*estrdup(char *);

 int	slurpdir(char *, Dir **);

--- a/objset.c

+++ b/objset.c

@@ -8,7 +8,7 @@

 {

 	s->sz = 16;

 	s->nobj = 0;

-	s->obj = emalloc(s->sz * sizeof(Hash));

+	s->obj = eamalloc(s->sz, sizeof(Hash));

 }

 void

@@ -41,7 +41,7 @@

 		s->sz *= 2;

 		s->nobj = 0;

-		s->obj = emalloc(s->sz * sizeof(Hash));

+		s->obj = eamalloc(s->sz, sizeof(Hash));

 		for(i = 0; i < sz; i++)

 			if(obj[i])

 				osadd(s, obj[i]);

--- a/ref.c

+++ b/ref.c

@@ -335,7 +335,7 @@

 		free(q);

 		q = n;

 	}

-	*res = emalloc(keep.nobj*sizeof(Object*));

+	*res = eamalloc(keep.nobj, sizeof(Object*));

 	*nres = 0;

 	for(i = 0; i < keep.sz; i++){

 		if(keep.obj[i] != nil && !oshas(&drop, keep.obj[i]->hash)){

@@ -568,7 +568,7 @@

 		free(ev.stk);

 		return -1;

 	}

-	h = emalloc(ev.nstk*sizeof(Hash));

+	h = eamalloc(ev.nstk, sizeof(Hash));

 	for(i = 0; i < ev.nstk; i++)

 		h[i] = ev.stk[i]->hash;

 	*r = h;

--- a/save.c

+++ b/save.c

@@ -240,8 +240,8 @@

 	r = -1;

 	nsub = 0;

 	nent = t->tree->nent;

-	ent = emalloc(nent * sizeof(*ent));

-	sub = emalloc((epath - path)*sizeof(Object*));

+	ent = eamalloc(nent, sizeof(*ent));

+	sub = eamalloc((epath - path), sizeof(Object*));

 	memcpy(ent, t->tree->ent, nent*sizeof(*ent));

 	for(p = path; p != epath; p = ep){

 		ne = pathelt(elt, sizeof(elt), *p + off, &isdir);

--- a/send.c

+++ b/send.c

@@ -41,8 +41,8 @@

 	if(sendall)

 		return listrefs(tailp, refp);

 	nu = 0;

-	tail = emalloc((nremoved + nbranch)*sizeof(Hash));

-	ref = emalloc((nremoved + nbranch)*sizeof(char*));

+	tail = eamalloc((nremoved + nbranch), sizeof(Hash));

+	ref = eamalloc((nremoved + nbranch), sizeof(char*));

 	for(i = 0; i < nbranch; i++){

 		ref[nu] = estrdup(branch[i]);

 		if(resolveref(&tail[nu], branch[i]) == -1)

@@ -108,7 +108,7 @@

 	first = 1;

 	nupd = readours(&ours, &refs);

-	theirs = emalloc(nupd*sizeof(Hash));

+	theirs = eamalloc(nupd, sizeof(Hash));

 	while(1){

 		n = readpkt(c, buf, sizeof(buf));

 		if(n == -1)

--- a/util.c

+++ b/util.c

@@ -8,6 +8,7 @@

 Hash Zhash;

 int chattygit;

+int hidepct;

 Object*

 emptydir(void)

@@ -61,11 +62,41 @@

 }

 void *

+eamalloc(ulong n, ulong sz)

+{

+	uvlong na;

+	void *v;

+

+	if((na = (uvlong)n*(uvlong)sz) >= (1ULL<<30))

+		sysfatal("alloc: overflow");

+	v = mallocz(na, 1);

+	if(v == nil)

+		sysfatal("malloc: %r");

+	setmalloctag(v, getcallerpc(&n));

+	return v;

+}

+

+void *

 erealloc(void *p, ulong n)

 {

 	void *v;

 	v = realloc(p, n);

+	if(v == nil)

+		sysfatal("realloc: %r");

+	setmalloctag(v, getcallerpc(&p));

+	return v;

+}

+

+void *

+earealloc(void *p, ulong n, ulong sz)

+{

+	uvlong na;

+	void *v;

+

+	if((na = (uvlong)n*(uvlong)sz) >= (1ULL<<30))

+		sysfatal("alloc: overflow");

+	v = realloc(p, na);

 	if(v == nil)

 		sysfatal("realloc: %r");

 	setmalloctag(v, getcallerpc(&p));