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 <[email protected]> Cc: Emese Revfy <[email protected]> Cc: Pax Team <[email protected]> Cc: Al Viro <[email protected]> Cc: Mateusz Guzik <[email protected]> Cc: Alexey Dobriyan <[email protected]> Cc: Cyrill Gorcunov <[email protected]> Cc: Jarod Wilson <[email protected]> --- 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; page = (char *)__get_free_page(GFP_TEMPORARY); -- 1.7.10.4
