proc: environ_read() make sure offset points to environment address range
Currently the following offset and environment address range check in
environ_read() of /proc/<pid>/environ is buggy:
int this_len = mm->env_end - (mm->env_start + src);
if (this_len <= 0)
break;
Large or negative offsets on /proc/<pid>/environ converted to 'unsigned
long' may pass this check since '(mm->env_start + src)' can overflow and
'this_len' will be positive.
This can turn /proc/<pid>/environ to act like /proc/<pid>/mem since
(mm->env_start + src) will point and read from another VMA.
There are two fixes here plus some code cleaning:
1) Fix the overflow by checking if the offset that was converted to
unsigned long will always point to the [mm->env_start, mm->env_end]
address range.
2) Remove the truncation that was made to the result of the check,
storing the result in 'int this_len' will alter its value and we can
not depend on it.
For kernels that have commit b409e578d ("proc: clean up
/proc/<pid>/environ handling") which adds the appropriate ptrace check and
saves the 'mm' at ->open() time, this is not a security issue.
This patch is taken from the grsecurity patch since it was just made
available.
Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Brad Spengler <spender@grsecurity.net>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 2772208..39ee093 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -827,15 +827,16 @@
if (!atomic_inc_not_zero(&mm->mm_users))
goto free;
while (count > 0) {
- int this_len, retval, max_len;
+ size_t this_len, max_len;
+ int retval;
+
+ if (src >= (mm->env_end - mm->env_start))
+ break;
this_len = mm->env_end - (mm->env_start + src);
- if (this_len <= 0)
- break;
-
- max_len = (count > PAGE_SIZE) ? PAGE_SIZE : count;
- this_len = (this_len > max_len) ? max_len : this_len;
+ max_len = min_t(size_t, PAGE_SIZE, count);
+ this_len = min(max_len, this_len);
retval = access_remote_vm(mm, (mm->env_start + src),
page, this_len, 0);