[glibc] libio: Flush-only _IO_str_overflow must not return EOF (bug 28949)

[Florian Weimer <fw@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=88ed43ff0cf2561481de7cba00686386794515d6

commit 88ed43ff0cf2561481de7cba00686386794515d6
Author: Florian Weimer <fweimer@redhat.com>
Date:   Fri Mar 18 21:27:54 2022 +0100

    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>

Diff:
---
 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 6a9a8846c4..1cd0bf6c3d 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 8e44f86c35..2aec314937 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;
 }