LibC+Kernel: Remove global variable use from snprintf and fprintf

The global variable use in these functions is super thread-unsafe and
means that any concurrent calls to sprintf or fprintf in a process
could race with each other and end up writing unexpected results.
We can just replace the function + global variable with a lambda that
captures the relevant argument when calling printf_internal instead.

1 files changed, 11 insertions, 20 deletions

diff --git a/Userland/Libraries/LibC/stdio.cpp b/Userland/Libraries/LibC/stdio.cpp
index 4fbd70e8aa..bc9091cd27 100644
--- a/Userland/Libraries/LibC/stdio.cpp
+++ b/Userland/Libraries/LibC/stdio.cpp
@@ -870,17 +870,10 @@ ALWAYS_INLINE void stdout_putch(char*&, char ch)
     putchar(ch);
 }
 
-static FILE* __current_stream = nullptr;
-ALWAYS_INLINE static void stream_putch(char*&, char ch)
-{
-    fputc(ch, __current_stream);
-}
-
 // https://pubs.opengroup.org/onlinepubs/9699919799/functions/vfprintf.html
 int vfprintf(FILE* stream, const char* fmt, va_list ap)
 {
-    __current_stream = stream;
-    return printf_internal(stream_putch, nullptr, fmt, ap);
+    return printf_internal([stream](auto, char ch) { fputc(ch, stream); }, nullptr, fmt, ap);
 }
 
 // https://pubs.opengroup.org/onlinepubs/9699919799/functions/fprintf.html
@@ -957,25 +950,23 @@ int sprintf(char* buffer, const char* fmt, ...)
     return ret;
 }
 
-static size_t __vsnprintf_space_remaining;
-ALWAYS_INLINE void sized_buffer_putch(char*& bufptr, char ch)
-{
-    if (__vsnprintf_space_remaining) {
-        *bufptr++ = ch;
-        --__vsnprintf_space_remaining;
-    }
-}
-
 // https://pubs.opengroup.org/onlinepubs/9699919799/functions/vsnprintf.html
 int vsnprintf(char* buffer, size_t size, const char* fmt, va_list ap)
 {
+    size_t space_remaining = 0;
     if (size) {
-        __vsnprintf_space_remaining = size - 1;
+        space_remaining = size - 1;
     } else {
-        __vsnprintf_space_remaining = 0;
+        space_remaining = 0;
     }
+    auto sized_buffer_putch = [&](char*& bufptr, char ch) {
+        if (space_remaining) {
+            *bufptr++ = ch;
+            --space_remaining;
+        }
+    };
     int ret = printf_internal(sized_buffer_putch, buffer, fmt, ap);
-    if (__vsnprintf_space_remaining) {
+    if (space_remaining) {
         buffer[ret] = '\0';
     } else if (size > 0) {
         buffer[size - 1] = '\0';