Commit 594cc251 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0b2c8f8b

arch/x86/include/asm/uaccess.h

+8 −1
Original line number Diff line number Diff line
@@ -705,7 +705,14 @@ extern struct movsl_mask { 
 * checking before using them, but you have to surround them with the

 * user_access_begin/end() pair.

 */

#define user_access_begin()	__uaccess_begin()

static __must_check inline bool user_access_begin(const void __user *ptr, size_t len)

{

	if (unlikely(!access_ok(ptr,len)))

		return 0;

	__uaccess_begin();

	return 1;

}

#define user_access_begin(a,b)	user_access_begin(a,b)

#define user_access_end()	__uaccess_end()



#define unsafe_put_user(x, ptr, err_label)					\

drivers/gpu/drm/i915/i915_gem_execbuffer.c

+13 −2
Original line number Diff line number Diff line
@@ -1624,7 +1624,9 @@ end_user: 
		 * happened we would make the mistake of assuming that the

		 * relocations were valid.

		 */

		user_access_begin();

		if (!user_access_begin(urelocs, size))

			goto end_user;



		for (copied = 0; copied < nreloc; copied++)

			unsafe_put_user(-1,

					&urelocs[copied].presumed_offset,
@@ -2606,7 +2608,16 @@ i915_gem_execbuffer2_ioctl(struct drm_device *dev, void *data, 
		unsigned int i;



		/* Copy the new buffer offsets back to the user's exec list. */

		user_access_begin();

		/*

		 * Note: count * sizeof(*user_exec_list) does not overflow,

		 * because we checked 'count' in check_buffer_count().

		 *

		 * And this range already got effectively checked earlier

		 * when we did the "copy_from_user()" above.

		 */

		if (!user_access_begin(user_exec_list, count * sizeof(*user_exec_list)))

			goto end_user;



		for (i = 0; i < args->buffer_count; i++) {

			if (!(exec2_list[i].offset & UPDATE))

				continue;

include/linux/uaccess.h

+1 −1
Original line number Diff line number Diff line
@@ -264,7 +264,7 @@ extern long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count); 
	probe_kernel_read(&retval, addr, sizeof(retval))



#ifndef user_access_begin

#define user_access_begin() do { } while (0)

#define user_access_begin(ptr,len) access_ok(ptr, len)

#define user_access_end() do { } while (0)

#define unsafe_get_user(x, ptr, err) do { if (unlikely(__get_user(x, ptr))) goto err; } while (0)

#define unsafe_put_user(x, ptr, err) do { if (unlikely(__put_user(x, ptr))) goto err; } while (0)

kernel/compat.c

+2 −4
Original line number Diff line number Diff line
@@ -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);

kernel/exit.c

+2 −4
Original line number Diff line number Diff line
@@ -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);

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