From: Mathias Krause <[email protected]>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
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 <[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]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Jiri Slaby <[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 293c987a5dab..582d34aaa56e 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -844,7 +844,8 @@ static ssize_t environ_read(struct file *file, char __user
*buf,
int ret = 0;
struct mm_struct *mm = file->private_data;
- 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);
--
2.8.2
