[PATCH] ntdll: Check for debug output buffer overflow in __wine_dbg_output().

[Józef Kucia]

This makes __wine_dbg_output() slightly more robust. The change prevents the
debug output buffer overflow when __wine_dbg_output() is called repeatedly
with small strings.

Signed-off-by: Józef Kucia 
---

Supersedes patch 164513.

---
 dlls/ntdll/debugtools.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/dlls/ntdll/debugtools.c b/dlls/ntdll/debugtools.c
index 64355ab3b841..027ca0236051 100644
--- a/dlls/ntdll/debugtools.c
+++ b/dlls/ntdll/debugtools.c
@@ -235,6 +235,7 @@ int __cdecl __wine_dbg_output( const char *str )
     struct debug_info *info = get_info();
     const char *end = strrchr( str, '\n' );
     int ret = 0;
+    size_t n;

if (end)
     {
@@ -243,7 +244,16 @@ int __cdecl __wine_dbg_output( const char *str )
         info->out_pos = 0;
         str = end + 1;
     }
-    if (*str) ret += append_output( info, str, strlen( str ));
+    if (*str)
+    {
+        n = strlen( str );
+        if (n >= sizeof(info->output) - info->out_pos && info->out_pos)
+        {
+            write( 2, info->output, info->out_pos );
+            info->out_pos = 0;
+        }
+        ret += append_output( info, str, n );
+    }
     return ret;
 }

[Alexandre Julliard]

Józef Kucia  writes:
> This makes __wine_dbg_output() slightly more robust. The change prevents the
> debug output buffer overflow when __wine_dbg_output() is called repeatedly
> with small strings.

The goal is to only output complete lines, otherwise it makes a mess of
the output. If some code overflows the line buffer that's a bug.

[Zebediah Figura]

On 5/13/19 5:42 AM, Alexandre Julliard wrote:
> Józef Kucia  writes:
> > This makes __wine_dbg_output() slightly more robust. The change prevents the
> > debug output buffer overflow when __wine_dbg_output() is called repeatedly
> > with small strings.
>
> The goal is to only output complete lines, otherwise it makes a mess of
> the output. If some code overflows the line buffer that's a bug.

While avoiding mixed output from multiple threads is certainly a 
desirable goal, I've been stymied multiple times by not being able to 
read very long strings in debug output [e.g.: GStreamer caps, parameters 
passed to MsiInstallProduct()]. How do you recommend we deal with those?

[Alexandre Julliard]

Zebediah Figura  writes:
> On 5/13/19 5:42 AM, Alexandre Julliard wrote:
> > Józef Kucia  writes:
> > > This makes __wine_dbg_output() slightly more robust. The change prevents the
> > > debug output buffer overflow when __wine_dbg_output() is called repeatedly
> > > with small strings.
> >
> > The goal is to only output complete lines, otherwise it makes a mess of
> > the output. If some code overflows the line buffer that's a bug.
>
> While avoiding mixed output from multiple threads is certainly a
> desirable goal, I've been stymied multiple times by not being able to
> read very long strings in debug output [e.g.: GStreamer caps,
> parameters passed to MsiInstallProduct()]. How do you recommend we
> deal with those?

You should make an effort to format the output properly, instead of
dumping everything on a single line. That's annoying to read even when
not mixed with other output.