From e8905ec27e2f4ea1b9f7e03df68a060b3ae6fca8 Mon Sep 17 00:00:00 2001 From: Djalal Harouni Date: Mon, 30 Jul 2012 14:42:26 -0700 Subject: 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//environ is buggy: int this_len = mm->env_end - (mm->env_start + src); if (this_len <= 0) break; Large or negative offsets on /proc//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//environ to act like /proc//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//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 Cc: Oleg Nesterov Cc: Brad Spengler Acked-by: Kees Cook Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/proc/base.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) (limited to 'fs') diff --git a/fs/proc/base.c b/fs/proc/base.c index 2772208338f8..39ee093b5e96 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -827,15 +827,16 @@ static ssize_t environ_read(struct file *file, char __user *buf, 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; - this_len = mm->env_end - (mm->env_start + src); - - if (this_len <= 0) + if (src >= (mm->env_end - mm->env_start)) break; - max_len = (count > PAGE_SIZE) ? PAGE_SIZE : count; - this_len = (this_len > max_len) ? max_len : this_len; + this_len = mm->env_end - (mm->env_start + src); + + 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); -- cgit v1.2.3