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authorLinus Torvalds <torvalds@linux-foundation.org>2019-01-04 20:56:09 (GMT)
committerLinus Torvalds <torvalds@linux-foundation.org>2019-01-04 20:56:09 (GMT)
commit594cc251fdd0d231d342d88b2fdff4bc42fb0690 (patch)
tree259269a399e6504a7cf8739201cf172d1cbb197a /lib
parent0b2c8f8b6b0c7530e2866c95862546d0da2057b0 (diff)
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 'lib')
-rw-r--r--lib/strncpy_from_user.c9
-rw-r--r--lib/strnlen_user.c9
2 files changed, 10 insertions, 8 deletions
diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
index b53e1b5..58eacd4 100644
--- a/lib/strncpy_from_user.c
+++ b/lib/strncpy_from_user.c
@@ -114,10 +114,11 @@ 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 60d0bbd..1c1a1b0 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;
}

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