From eb5a13ddc30824c20f1e2b662d2c821ad3808526 Mon Sep 17 00:00:00 2001

From: Linus Torvalds torvalds@linux-foundation.org Date: Fri, 4 Jan 2019 12:56:09 -0800 Subject: [PATCH] make 'user_access_begin()' do 'access_ok()'

[ Upstream commit 594cc251fdd0d231d342d88b2fdff4bc42fb0690 ]

Fixes CVE-2018-20669 Backported from v5.0-rc1 Patch 1/1

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 --- Rationale: When working on stability and security for a project with 4.14 kernel, i backported patches from upstream. Want to give this work back to the community, as 4.14 is a SLTS. --- arch/x86/include/asm/uaccess.h | 9 ++++++++- drivers/gpu/drm/i915/i915_gem_execbuffer.c | 15 +++++++++++++-- include/linux/uaccess.h | 2 +- kernel/compat.c | 6 ++---- kernel/exit.c | 6 ++---- lib/strncpy_from_user.c | 9 +++++---- lib/strnlen_user.c | 9 +++++---- 7 files changed, 36 insertions(+), 20 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index 971830341061..fd00c5fba059 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -711,7 +711,14 @@ 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(VERIFY_READ,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) \ diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c index d99d05a91032..3a65a45184ad 100644 --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c @@ -1566,7 +1566,9 @@ static int eb_copy_relocations(const struct i915_execbuffer *eb) * 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, @@ -2649,7 +2651,16 @@ i915_gem_execbuffer2(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: args->buffer_count * sizeof(*user_exec_list) does not overflow, + * because we checked this on entry. + * + * And this range already got effectively checked earlier + * when we did the "copy_from_user()" above. + */ + if (!user_access_begin(user_exec_list, args->buffer_count * sizeof(*user_exec_list))) + goto end_user; + for (i = 0; i < args->buffer_count; i++) { if (!(exec2_list[i].offset & UPDATE)) continue; diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index 251e655d407f..76407748701b 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -267,7 +267,7 @@ 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) diff --git a/kernel/compat.c b/kernel/compat.c index 7e83733d4c95..a9f5de63dc90 100644 --- a/kernel/compat.c +++ b/kernel/compat.c @@ -437,10 +437,9 @@ 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(VERIFY_READ, 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); @@ -467,10 +466,9 @@ 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(VERIFY_WRITE, 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 d1baf9c96c3e..c3ad546ba7c2 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -1597,10 +1597,9 @@ SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *, if (!infop) return err;

- if (!access_ok(VERIFY_WRITE, 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); @@ -1725,10 +1724,9 @@ COMPAT_SYSCALL_DEFINE5(waitid, if (!infop) return err;

- if (!access_ok(VERIFY_WRITE, 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); diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c index e304b54c9c7d..023ba9f3b99f 100644 --- a/lib/strncpy_from_user.c +++ b/lib/strncpy_from_user.c @@ -115,10 +115,11 @@ long strncpy_from_user(char *dst, const char __user *src, long count)

kasan_check_write(dst, count); check_object_size(dst, count, false); - user_access_begin(); - retval = do_strncpy_from_user(dst, src, count, max); - user_access_end(); - return retval; + if (user_access_begin(src, max)) { + retval = do_strncpy_from_user(dst, src, count, max); + user_access_end(); + return retval; + } } return -EFAULT; } diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c index 184f80f7bacf..7f2db3fe311f 100644 --- a/lib/strnlen_user.c +++ b/lib/strnlen_user.c @@ -114,10 +114,11 @@ long strnlen_user(const char __user *str, long count) unsigned long max = max_addr - src_addr; long retval;

- user_access_begin(); - retval = do_strnlen_user(str, count, max); - user_access_end(); - return retval; + if (user_access_begin(str, max)) { + retval = do_strnlen_user(str, count, max); + user_access_end(); + return retval; + } } return 0; } -- 2.17.1 ----------------- Mentor Graphics (Deutschland) GmbH, Arnulfstraße 201, 80634 München / Germany Registergericht München HRB 106955, Geschäftsführer: Thomas Heurung, Alexander Walter