Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 4.5 51/88] proc: prevent accessing /proc/<PID>/environ until its ready | Date | Mon, 9 May 2016 09:21:40 +0200 |
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4.5-stable review patch. If anyone has any objections, please let me know.
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From: Mathias Krause <minipli@googlemail.com>
commit 8148a73c9901a8794a50f950083c00ccf97d43b3 upstream.
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.
The expected consequence is that userland trying to access /proc/<PID>/environ of a not yet fully set up process may get inconsistent data as we're in the middle of copying in the environment variables.
Fixes: https://forums.grsecurity.net/viewtopic.php?f=3&t=4363 Fixes: 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> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- fs/proc/base.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -955,7 +955,8 @@ static ssize_t environ_read(struct file 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; page = (char *)__get_free_page(GFP_TEMPORARY);
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