[Qemu-devel] [PATCH] cutils: Assert in-range base for string-to-integer conversions

[Eric Blake <eblake@redhat.com>]

POSIX states that the value of endptr is unspecified if strtol()
fails with EINVAL due to an invalid base argument.  Since none of
the callers to check_strtox_error() initialized endptr, we could
end up propagating uninitialized data back to a caller on error.
However, passing an out-of-range base is already a sign of poor
programming, so let's just assert that base is in range, at which
point check_strtox_error() can be tightened to assert that it is
receiving an initialized ep that points somewhere within the
caller's original string, regardless of whether strto*() succeeded
or failed with ERANGE.

Reported-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
---

Also tested that this does not negatively impact David's pending
additions of qemu_strtod{,_finite}().  Thus:
Based-on: <20181121164421.20780-1-david@redhat.com>

 util/cutils.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/util/cutils.c b/util/cutils.c
index 91930d1bbeb..e098debdc0c 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -278,6 +278,7 @@ int qemu_strtosz_metric(const char *nptr, const char **end, uint64_t *result)
 static int check_strtox_error(const char *nptr, char *ep,
                               const char **endptr, int libc_errno)
 {
+    assert(ep >= nptr);
     if (endptr) {
         *endptr = ep;
     }
@@ -325,6 +326,7 @@ int qemu_strtoi(const char *nptr, const char **endptr, int base,
     char *ep;
     long long lresult;

+    assert((unsigned) base <= 36 && base != 1);
     if (!nptr) {
         if (endptr) {
             *endptr = nptr;
@@ -377,6 +379,7 @@ int qemu_strtoui(const char *nptr, const char **endptr, int base,
     char *ep;
     long long lresult;

+    assert((unsigned) base <= 36 && base != 1);
     if (!nptr) {
         if (endptr) {
             *endptr = nptr;
@@ -433,6 +436,7 @@ int qemu_strtol(const char *nptr, const char **endptr, int base,
 {
     char *ep;

+    assert((unsigned) base <= 36 && base != 1);
     if (!nptr) {
         if (endptr) {
             *endptr = nptr;
@@ -475,6 +479,7 @@ int qemu_strtoul(const char *nptr, const char **endptr, int base,
 {
     char *ep;

+    assert((unsigned) base <= 36 && base != 1);
     if (!nptr) {
         if (endptr) {
             *endptr = nptr;
@@ -502,6 +507,7 @@ int qemu_strtoi64(const char *nptr, const char **endptr, int base,
 {
     char *ep;

+    assert((unsigned) base <= 36 && base != 1);
     if (!nptr) {
         if (endptr) {
             *endptr = nptr;
@@ -525,6 +531,7 @@ int qemu_strtou64(const char *nptr, const char **endptr, int base,
 {
     char *ep;

+    assert((unsigned) base <= 36 && base != 1);
     if (!nptr) {
         if (endptr) {
             *endptr = nptr;
@@ -657,6 +664,7 @@ int parse_uint(const char *s, unsigned long long *value, char **endptr,
     char *endp = (char *)s;
     unsigned long long val = 0;

+    assert((unsigned) base <= 36 && base != 1);
     if (!s) {
         r = -EINVAL;
         goto out;
-- 
2.17.2