Re: [PATCH v3] libio: do not unbuffer legacy standard files in compatibility mode [BZ #24228]

[Florian Weimer <fweimer@redhat.com>]

* Dmitry V. Levin:

> Commit glibc-2.23~693 (a601b74d31ca086de38441d316a3dee24c866305)

Please quote the commit hash and commit subject, kernel-style.  (How did
you determine this reference, anyway?)

> diff --git a/libio/genops.c b/libio/genops.c
> index 2a0d9b81df..aa92d61b6b 100644
> --- a/libio/genops.c
> +++ b/libio/genops.c
> @@ -789,6 +789,10 @@ _IO_unbuffer_all (void)
>  
>    for (fp = (FILE *) _IO_list_all; fp; fp = fp->_chain)
>      {
> +#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_1)
> +      if (__glibc_unlikely (&_IO_stdin_used == NULL) && _IO_legacy_file (fp))
> +	continue;
> +#endif

I wonder if we should check _IO_legacy_file only here.  This is related
to the previous discussion.

> diff --git a/libio/tst-bz24228.c b/libio/tst-bz24228.c
> new file mode 100644
> index 0000000000..3692f14b71
> --- /dev/null
> +++ b/libio/tst-bz24228.c
> @@ -0,0 +1,30 @@
> +/* BZ #24228 check for memory corruption in legacy libio
> +
> +   Copyright (C) 2019 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.

We do not generally have a blank line for the “Copyright” line, I think.

> +#include <mcheck.h>
> +#include <support/test-driver.h>
> +
> +static int
> +do_test (void)
> +{
> +  mtrace ();
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/libio/tst-bz24228.map b/libio/tst-bz24228.map
> new file mode 100644
> index 0000000000..ecb8c058f5
> --- /dev/null
> +++ b/libio/tst-bz24228.map
> @@ -0,0 +1,3 @@
> +{
> +  local: _IO_stdin_used;
> +};

Please add a comment to the file why you are doing this, something like
“hide the symbol from libc.so.6 to switch to the libio/oldfileops.c
implementation (if it is available for the architecture)”.

Thanks,
Florian