[glibc/release/2.38/master] libio: Check remaining buffer size in _IO_wdo_write (bug 31183)

[glibc/release/2.38/master] libio: Check remaining buffer size in _IO_wdo_write (bug 31183)

[Florian Weimer]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=cfe121910013a46e2477562282c56ae8062089aa

commit cfe121910013a46e2477562282c56ae8062089aa
Author: Florian Weimer <fweimer@redhat.com>
Date:   Tue Jan 2 14:36:17 2024 +0100

    libio: Check remaining buffer size in _IO_wdo_write (bug 31183)
    
    The multibyte character needs to fit into the remaining buffer space,
    not the already-written buffer space.  Without the fix, we were never
    moving the write pointer from the start of the buffer, always using
    the single-character fallback buffer.
    
    Fixes commit 04b76b5aa8b2d1d19066e42dd1 ("Don't error out writing
    a multibyte character to an unbuffered stream (bug 17522)").
    
    (cherry picked from commit ecc7c3deb9f347649c2078fcc0f94d4cedf92d60)

Diff:
---
 NEWS             | 1 +
 libio/wfileops.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/NEWS b/NEWS
index 905230b838..6768c2da6f 100644
--- a/NEWS
+++ b/NEWS
@@ -43,6 +43,7 @@ The following bugs are resolved with this release:
     -D_FILE_OFFSET_BITS=64
   [30842] Stack read overflow in getaddrinfo in no-aaaa mode (CVE-2023-4527)
   [30843] potential use-after-free in getcanonname (CVE-2023-4806)
+  [31183] Wide stream buffer size reduced MB_LEN_MAX bytes after bug 17522 fix
   [31184] FAIL: elf/tst-tlsgap
   [31185] Incorrect thread point access in _dl_tlsdesc_undefweak and _dl_tlsdesc_dynamic
 
diff --git a/libio/wfileops.c b/libio/wfileops.c
index f16f6db1c3..9ab8f2e7f3 100644
--- a/libio/wfileops.c
+++ b/libio/wfileops.c
@@ -55,7 +55,7 @@ _IO_wdo_write (FILE *fp, const wchar_t *data, size_t to_do)
 	  char mb_buf[MB_LEN_MAX];
 	  char *write_base, *write_ptr, *buf_end;
 
-	  if (fp->_IO_write_ptr - fp->_IO_write_base < sizeof (mb_buf))
+	  if (fp->_IO_buf_end - fp->_IO_write_ptr < sizeof (mb_buf))
 	    {
 	      /* Make sure we have room for at least one multibyte
 		 character.  */