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SubjectRe: [PATCH] proc: prevent accessing /proc/<PID>/environ until it's ready
On Thu, Apr 28, 2016 at 09:04:18PM +0200, Mathias Krause wrote:
> If /proc/<PID>/environ gets read before the envp[] array is fully set
> up in create_{aout,elf,elf_fdpic,flat}_tables(), we might end up trying
> to read more bytes than are actually written, as env_start will already
> be set but env_end will still be zero, making the range calculation
> underflow, allowing to read beyond the end of what has been written.
>
> Fix this as it is done for /proc/<PID>/cmdline by testing env_end for
> zero. It is, apparently, intentionally set last in create_*_tables().
>
> This bug was found by the PaX size_overflow plugin that detected the
> arithmetic underflow of 'this_len = env_end - (env_start + src)' when
> env_end is still zero.
>
> Reported-at: https://forums.grsecurity.net/viewtopic.php?f=3&t=4363
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=116461
> Signed-off-by: Mathias Krause <minipli@googlemail.com>
> Cc: Emese Revfy <re.emese@gmail.com>
> Cc: Pax Team <pageexec@freemail.hu>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Mateusz Guzik <mguzik@redhat.com>
> Cc: Alexey Dobriyan <adobriyan@gmail.com>
> Cc: Cyrill Gorcunov <gorcunov@openvz.org>
> Cc: Jarod Wilson <jarod@redhat.com>
> ---
> fs/proc/base.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 4f764c2ac1a5..45f2162e55b2 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -955,7 +955,8 @@ static ssize_t environ_read(struct file *file, char __user *buf,
> struct mm_struct *mm = file->private_data;
> unsigned long env_start, env_end;
>
> - if (!mm)
> + /* Ensure the process spawned far enough to have an environment. */
> + if (!mm || !mm->env_end)
> return 0;

At least in proc_pid_cmdline_read such test is done.
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>

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