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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2019-01-04 23:56:09 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-06-22 10:04:58 +0300 |
| commit | 216284c4a126b28469eb0bf4994c669e251f47ba (patch) | |
| tree | 2b454ee3dc77dee76acd2792159cf8e71716d83a /lib | |
| parent | 6f89ad2e79c3d67b8390d74666225b7489e3f280 (diff) | |
| download | linux-216284c4a126b28469eb0bf4994c669e251f47ba.tar.xz | |
make 'user_access_begin()' do 'access_ok()'
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>
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/strncpy_from_user.c | 9 | ||||
| -rw-r--r-- | lib/strnlen_user.c | 9 |
2 files changed, 10 insertions, 8 deletions
diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c index e304b54c9c7d..b8570a11776d 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(VERIFY_READ, 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..f5fa5b266ea2 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(VERIFY_READ, str, max)) { + retval = do_strnlen_user(str, count, max); + user_access_end(); + return retval; + } } return 0; } |