From 594cc251fdd0d231d342d88b2fdff4bc42fb0690 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Fri, 4 Jan 2019 12:56:09 -0800 Subject: make 'user_access_begin()' do 'access_ok()' Originally, the rule used to be that you'd have to do access_ok() separately, and then user_access_begin() before actually doing the direct (optimized) user access. But experience has shown that people then decide not to do access_ok() at all, and instead rely on it being implied by other operations or similar. Which makes it very hard to verify that the access has actually been range-checked. If you use the unsafe direct user accesses, hardware features (either SMAP - Supervisor Mode Access Protection - on x86, or PAN - Privileged Access Never - on ARM) do force you to use user_access_begin(). But nothing really forces the range check. By putting the range check into user_access_begin(), we actually force people to do the right thing (tm), and the range check vill be visible near the actual accesses. We have way too long a history of people trying to avoid them. Signed-off-by: Linus Torvalds --- kernel/compat.c | 6 ++---- kernel/exit.c | 6 ++---- 2 files changed, 4 insertions(+), 8 deletions(-) (limited to 'kernel') diff --git a/kernel/compat.c b/kernel/compat.c index 705d4ae6c018..f01affa17e22 100644 --- a/kernel/compat.c +++ b/kernel/compat.c @@ -354,10 +354,9 @@ long compat_get_bitmap(unsigned long *mask, const compat_ulong_t __user *umask, bitmap_size = ALIGN(bitmap_size, BITS_PER_COMPAT_LONG); nr_compat_longs = BITS_TO_COMPAT_LONGS(bitmap_size); - if (!access_ok(umask, bitmap_size / 8)) + if (!user_access_begin(umask, bitmap_size / 8)) return -EFAULT; - user_access_begin(); while (nr_compat_longs > 1) { compat_ulong_t l1, l2; unsafe_get_user(l1, umask++, Efault); @@ -384,10 +383,9 @@ long compat_put_bitmap(compat_ulong_t __user *umask, unsigned long *mask, bitmap_size = ALIGN(bitmap_size, BITS_PER_COMPAT_LONG); nr_compat_longs = BITS_TO_COMPAT_LONGS(bitmap_size); - if (!access_ok(umask, bitmap_size / 8)) + if (!user_access_begin(umask, bitmap_size / 8)) return -EFAULT; - user_access_begin(); while (nr_compat_longs > 1) { unsigned long m = *mask++; unsafe_put_user((compat_ulong_t)m, umask++, Efault); diff --git a/kernel/exit.c b/kernel/exit.c index 8a01b671dc1f..2d14979577ee 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -1604,10 +1604,9 @@ SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *, if (!infop) return err; - if (!access_ok(infop, sizeof(*infop))) + if (!user_access_begin(infop, sizeof(*infop))) return -EFAULT; - user_access_begin(); unsafe_put_user(signo, &infop->si_signo, Efault); unsafe_put_user(0, &infop->si_errno, Efault); unsafe_put_user(info.cause, &infop->si_code, Efault); @@ -1732,10 +1731,9 @@ COMPAT_SYSCALL_DEFINE5(waitid, if (!infop) return err; - if (!access_ok(infop, sizeof(*infop))) + if (!user_access_begin(infop, sizeof(*infop))) return -EFAULT; - user_access_begin(); unsafe_put_user(signo, &infop->si_signo, Efault); unsafe_put_user(0, &infop->si_errno, Efault); unsafe_put_user(info.cause, &infop->si_code, Efault); -- cgit v1.2.3-59-g8ed1b