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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2019-01-04 12:56:09 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-01-04 12:56:09 -0800 |
| commit | 594cc251fdd0d231d342d88b2fdff4bc42fb0690 (patch) | |
| tree | 259269a399e6504a7cf8739201cf172d1cbb197a /kernel | |
| parent | 0b2c8f8b6b0c7530e2866c95862546d0da2057b0 (diff) | |
| download | lwn-594cc251fdd0d231d342d88b2fdff4bc42fb0690.tar.gz lwn-594cc251fdd0d231d342d88b2fdff4bc42fb0690.zip | |
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 <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/compat.c | 6 | ||||
| -rw-r--r-- | kernel/exit.c | 6 |
2 files changed, 4 insertions, 8 deletions
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); |