[pulseaudio-discuss] [PATCH] core-util: Make number parsing stricter

[Tanu Kaskinen]

pa_atou(), pa_atol() and pa_atod() are stricter than the libc
counterparts (the PA functions reject strings that have trailing extra
stuff in them). I have been under the impression that the PA functions
only accept "obviously valid numbers", that is, I have assumed that
these would be rejected: " 42" (leading whitespace), "" (empty
string) and "-18446744073709551615" in case of pa_atou().

I noticed that empty strings are accepted, however, and on closer
inspection I found that leading whitespace is accepted too, and even
that pa_atou() thinks that "-18446744073709551615" is the same thing
as "1"! This patch makes the parsing functions more strict, so that
they indeed only accept "obviously valid numbers". In case of
pa_atou() I decided to also disallow a leading plus sign, as it's
redundant, and looks very strange (i.e. not obviously valid) in
contexts where the number represents, for example, an array index.
---
 src/pulsecore/core-util.c | 41 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 38 insertions(+), 3 deletions(-)

diff --git a/src/pulsecore/core-util.c b/src/pulsecore/core-util.c
index 9b16936..e20ebcb 100644
--- a/src/pulsecore/core-util.c
+++ b/src/pulsecore/core-util.c
@@ -2315,10 +2315,27 @@ int pa_atou(const char *s, uint32_t *ret_u) {
     pa_assert(s);
     pa_assert(ret_u);
 
+    /* strtoul() ignores leading spaces. We don't. */
+    if (isspace(*s)) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    /* strtoul() accepts strings that start with a minus sign. In that case the
+     * original negative number gets negated, and strtoul() returns the negated
+     * result. We don't want that kind of behaviour. strtoul() also allows a
+     * leading plus sign, which is also a thing that we don't want. */
+    if (*s == '-' || *s == '+') {
+        errno = EINVAL;
+        return -1;
+    }
+
     errno = 0;
     l = strtoul(s, &x, 0);
 
-    if (!x || *x || errno) {
+    /* If x doesn't point to the end of s, there was some trailing garbage in
+     * the string. If x points to s, no conversion was done (empty string). */
+    if (!x || *x || x == s || errno) {
         if (!errno)
             errno = EINVAL;
         return -1;
@@ -2342,10 +2359,19 @@ int pa_atol(const char *s, long *ret_l) {
     pa_assert(s);
     pa_assert(ret_l);
 
+    /* strtol() ignores leading spaces. We don't. */
+    if (isspace(*s)) {
+        errno = EINVAL;
+        return -1;
+    }
+
     errno = 0;
     l = strtol(s, &x, 0);
 
-    if (!x || *x || errno) {
+    /* If x doesn't point to the end of s, there was some trailing garbage in
+     * the string. If x points to s, no conversion was done (at least an empty
+     * string can trigger this). */
+    if (!x || *x || x == s || errno) {
         if (!errno)
             errno = EINVAL;
         return -1;
@@ -2371,6 +2397,12 @@ int pa_atod(const char *s, double *ret_d) {
     pa_assert(s);
     pa_assert(ret_d);
 
+    /* strtod() ignores leading spaces. We don't. */
+    if (isspace(*s)) {
+        errno = EINVAL;
+        return -1;
+    }
+
     /* This should be locale independent */
 
 #ifdef HAVE_STRTOF_L
@@ -2392,7 +2424,10 @@ int pa_atod(const char *s, double *ret_d) {
         f = strtod(s, &x);
     }
 
-    if (!x || *x || errno) {
+    /* If x doesn't point to the end of s, there was some trailing garbage in
+     * the string. If x points to s, no conversion was done (at least an empty
+     * string can trigger this). */
+    if (!x || *x || x == s || errno) {
         if (!errno)
             errno = EINVAL;
         return -1;
-- 
1.9.3