From 88ed43ff0cf2561481de7cba00686386794515d6 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Fri, 18 Mar 2022 21:27:54 +0100
Subject: [PATCH] libio: Flush-only _IO_str_overflow must not return EOF (bug
 28949)

In general, _IO_str_overflow returns the character passed as an argument
on success.  However, if flush-only operation is requested by passing
EOF, returning EOF looks like an error, and the caller cannot tell
whether the operation was successful or not.

_IO_wstr_overflow had the same bug regarding WEOF.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
---
 libio/strops.c  | 5 ++++-
 libio/wstrops.c | 5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/libio/strops.c b/libio/strops.c
index 6a9a884..1cd0bf6 100644
--- a/libio/strops.c
+++ b/libio/strops.c
@@ -133,7 +133,10 @@ _IO_str_overflow (FILE *fp, int c)
     *fp->_IO_write_ptr++ = (unsigned char) c;
   if (fp->_IO_write_ptr > fp->_IO_read_end)
     fp->_IO_read_end = fp->_IO_write_ptr;
-  return c;
+  if (flush_only)
+    return 0;
+  else
+    return c;
 }
 libc_hidden_def (_IO_str_overflow)
 
diff --git a/libio/wstrops.c b/libio/wstrops.c
index 8e44f86..2aec3149 100644
--- a/libio/wstrops.c
+++ b/libio/wstrops.c
@@ -130,7 +130,10 @@ _IO_wstr_overflow (FILE *fp, wint_t c)
     *fp->_wide_data->_IO_write_ptr++ = c;
   if (fp->_wide_data->_IO_write_ptr > fp->_wide_data->_IO_read_end)
     fp->_wide_data->_IO_read_end = fp->_wide_data->_IO_write_ptr;
-  return c;
+  if (flush_only)
+    return 0;
+  else
+    return c;
 }
 
 
-- 
1.8.3.1

