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authorLinus Torvalds <torvalds@linux-foundation.org>2019-01-04 23:56:09 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2019-01-04 23:56:09 +0300
commit594cc251fdd0d231d342d88b2fdff4bc42fb0690 (patch)
tree259269a399e6504a7cf8739201cf172d1cbb197a /lib/strncpy_from_user.c
parent0b2c8f8b6b0c7530e2866c95862546d0da2057b0 (diff)
downloadlinux-594cc251fdd0d231d342d88b2fdff4bc42fb0690.tar.xz
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/strncpy_from_user.c')
-rw-r--r--lib/strncpy_from_user.c9
1 files changed, 5 insertions, 4 deletions
diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
index b53e1b5d80f4..58eacd41526c 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;
}