[PATCH] libio: Check remaining buffer size in _IO_wdo_write (bug 31183)

[PATCH] libio: Check remaining buffer size in _IO_wdo_write (bug 31183)

[Florian Weimer]

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)").

---
 libio/wfileops.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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.  */

base-commit: 61bac1a9d2ab80ebcbc51484722e6ea43414bec7

Re: [PATCH] libio: Check remaining buffer size in _IO_wdo_write (bug 31183)

[Andreas Schwab]

On Dez 20 2023, Florian Weimer wrote:

> 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)").

Ok.

I don't know how I managed to get that so wrong.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."