From 8148a73c9901a8794a50f950083c00ccf97d43b3 Mon Sep 17 00:00:00 2001 From: Mathias Krause Date: Thu, 5 May 2016 16:22:26 -0700 Subject: [PATCH] proc: prevent accessing /proc//environ until it's ready If /proc//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//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//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 Cc: Emese Revfy Cc: Pax Team Cc: Al Viro Cc: Mateusz Guzik Cc: Alexey Dobriyan Cc: Cyrill Gorcunov Cc: Jarod Wilson Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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 b1755b23893e..92e37e224cd2 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); -- 2.34.1