From: Linus Torvalds torvalds@linux-foundation.org
commit 594cc251fdd0d231d342d88b2fdff4bc42fb0690 upstream.
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 Signed-off-by: Miles Chen miles.chen@mediatek.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/uaccess.h | 12 +++++++++++- drivers/gpu/drm/i915/i915_gem_execbuffer.c | 17 +++++++++++++++-- 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, 41 insertions(+), 20 deletions(-)
--- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -711,7 +711,17 @@ 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(int type, + const void __user *ptr, + size_t len) +{ + if (unlikely(!access_ok(type, ptr, len))) + return 0; + __uaccess_begin(); + return 1; +} + +#define user_access_begin(a, b, c) user_access_begin(a, b, c) #define user_access_end() __uaccess_end()
#define unsafe_put_user(x, ptr, err_label) \ --- 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 str * happened we would make the mistake of assuming that the * relocations were valid. */ - user_access_begin(); + if (!user_access_begin(VERIFY_WRITE, urelocs, size)) + goto end_user; + for (copied = 0; copied < nreloc; copied++) unsafe_put_user(-1, &urelocs[copied].presumed_offset, @@ -2601,6 +2603,7 @@ i915_gem_execbuffer2(struct drm_device * struct drm_i915_gem_execbuffer2 *args = data; struct drm_i915_gem_exec_object2 *exec2_list; struct drm_syncobj **fences = NULL; + const size_t count = args->buffer_count; int err;
if (args->buffer_count < 1 || args->buffer_count > SIZE_MAX / sz - 1) { @@ -2649,7 +2652,17 @@ i915_gem_execbuffer2(struct drm_device * 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(VERIFY_WRITE, 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; --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -267,7 +267,7 @@ extern long strncpy_from_unsafe(char *ds probe_kernel_read(&retval, addr, sizeof(retval))
#ifndef user_access_begin -#define user_access_begin() do { } while (0) +#define user_access_begin(type, ptr, len) access_ok(type, 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) --- a/kernel/compat.c +++ b/kernel/compat.c @@ -437,10 +437,9 @@ long compat_get_bitmap(unsigned long *ma 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(VERIFY_READ, 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 __ 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(VERIFY_WRITE, 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); --- a/kernel/exit.c +++ b/kernel/exit.c @@ -1597,10 +1597,9 @@ SYSCALL_DEFINE5(waitid, int, which, pid_ if (!infop) return err;
- if (!access_ok(VERIFY_WRITE, infop, sizeof(*infop))) + if (!user_access_begin(VERIFY_WRITE, 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(VERIFY_WRITE, 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); --- a/lib/strncpy_from_user.c +++ b/lib/strncpy_from_user.c @@ -115,10 +115,11 @@ long strncpy_from_user(char *dst, const
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(VERIFY_READ, src, max)) { + retval = do_strncpy_from_user(dst, src, count, max); + user_access_end(); + return retval; + } } return -EFAULT; } --- a/lib/strnlen_user.c +++ b/lib/strnlen_user.c @@ -114,10 +114,11 @@ long strnlen_user(const char __user *str 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(VERIFY_READ, str, max)) { + retval = do_strnlen_user(str, count, max); + user_access_end(); + return retval; + } } return 0; }