musl: handle wcsnrtombs destination buffer overflow (CVE-2020-28928)

The wcsnrtombs function in all musl libc versions up through 1.2.1 has been found to have multiple bugs in handling of destination buffer size when limiting the input character count, which can lead to infinite loop with no forward progress (no overflow) or writing past the end of the destination buffera. This function is not used internally in musl and is not widely used, but does appear in some applications. The non-input-limiting form wcsrtombs is not affected. All users of musl 1.2.1 and prior versions should apply the attached patch, which replaces the overly complex and erroneous implementation. The upcoming 1.2.2 release will adopt this new implementation. Signed-off-by: Petr Štetiar <[email protected]> (cherry picked from commit 4d4ef10)
sidpixel · Nov 23, 2020 · 733a482 · 733a482
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commit 733a482
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diff --git a/toolchain/musl/common.mk b/toolchain/musl/common.mk
@@ -9,7 +9,7 @@ include $(INCLUDE_DIR)/target.mk
 
 PKG_NAME:=musl
 PKG_VERSION:=1.1.24
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_SUBDIR:=$(PKG_NAME)-$(PKG_VERSION)

diff --git a/toolchain/musl/patches/700-wcsnrtombs-cve-2020-28928.diff b/toolchain/musl/patches/700-wcsnrtombs-cve-2020-28928.diff
@@ -0,0 +1,65 @@
+diff --git a/src/multibyte/wcsnrtombs.c b/src/multibyte/wcsnrtombs.c
+index 676932b5..95e25e70 100644
+--- a/src/multibyte/wcsnrtombs.c
++++ b/src/multibyte/wcsnrtombs.c
+@@ -1,41 +1,33 @@
+ #include <wchar.h>
++#include <limits.h>
++#include <string.h>
+
+ size_t wcsnrtombs(char *restrict dst, const wchar_t **restrict wcs, size_t wn, size_t n, mbstate_t *restrict st)
+ {
+-	size_t l, cnt=0, n2;
+-	char *s, buf[256];
+ 	const wchar_t *ws = *wcs;
+-	const wchar_t *tmp_ws;
+-
+-	if (!dst) s = buf, n = sizeof buf;
+-	else s = dst;
+-
+-	while ( ws && n && ( (n2=wn)>=n || n2>32 ) ) {
+-		if (n2>=n) n2=n;
+-		tmp_ws = ws;
+-		l = wcsrtombs(s, &ws, n2, 0);
+-		if (!(l+1)) {
+-			cnt = l;
+-			n = 0;
++	size_t cnt = 0;
++	if (!dst) n=0;
++	while (ws && wn) {
++		char tmp[MB_LEN_MAX];
++		size_t l = wcrtomb(n<MB_LEN_MAX ? tmp : dst, *ws, 0);
++		if (l==-1) {
++			cnt = -1;
+ 			break;
+ 		}
+-		if (s != buf) {
+-			s += l;
++		if (dst) {
++			if (n<MB_LEN_MAX) {
++				if (l>n) break;
++				memcpy(dst, tmp, l);
++			}
++			dst += l;
+ 			n -= l;
+ 		}
+-		wn = ws ? wn - (ws - tmp_ws) : 0;
+-		cnt += l;
+-	}
+-	if (ws) while (n && wn) {
+-		l = wcrtomb(s, *ws, 0);
+-		if ((l+1)<=1) {
+-			if (!l) ws = 0;
+-			else cnt = l;
++		if (!*ws) {
++			ws = 0;
+ 			break;
+ 		}
+-		ws++; wn--;
+-		/* safe - this loop runs fewer than sizeof(buf) times */
+-		s+=l; n-=l;
++		ws++;
++		wn--;
+ 		cnt += l;
+ 	}
+ 	if (dst) *wcs = ws;