Fix: compat_rw_copy_check_uvector() misuse in aio, readv, writev, and security keys

Looking at mm/process_vm_access.c:process_vm_rw() and comparing it to
compat_process_vm_rw() shows that the compatibility code requires an
explicit "access_ok()" check before calling
compat_rw_copy_check_uvector(). The same difference seems to appear when
we compare fs/read_write.c:do_readv_writev() to
fs/compat.c:compat_do_readv_writev().

This subtle difference between the compat and non-compat requirements
should probably be debated, as it seems to be error-prone. In fact,
there are two others sites that use this function in the Linux kernel,
and they both seem to get it wrong:

Now shifting our attention to fs/aio.c, we see that aio_setup_iocb()
also ends up calling compat_rw_copy_check_uvector() through
aio_setup_vectored_rw(). Unfortunately, the access_ok() check appears to
be missing. Same situation for
security/keys/compat.c:compat_keyctl_instantiate_key_iov().

I propose that we add the access_ok() check directly into
compat_rw_copy_check_uvector(), so callers don't have to worry about it,
and it therefore makes the compat call code similar to its non-compat
counterpart. Place the access_ok() check in the same location where
copy_from_user() can trigger a -EFAULT error in the non-compat code, so
the ABI behaviors are alike on both compat and non-compat.

While we are here, fix compat_do_readv_writev() so it checks for
compat_rw_copy_check_uvector() negative return values.

And also, fix a memory leak in compat_keyctl_instantiate_key_iov() error
handling.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/security/keys/compat.c b/security/keys/compat.c
index 1c261763f479..d65fa7fa29ba 100644
--- a/security/keys/compat.c
+++ b/security/keys/compat.c
@@ -40,12 +40,12 @@ static long compat_keyctl_instantiate_key_iov(
                                            ARRAY_SIZE(iovstack),
                                            iovstack, &iov);
         if (ret < 0)
-                return ret;
+                goto err;
         if (ret == 0)
                 goto no_payload_free;
 
         ret = keyctl_instantiate_key_common(id, iov, ioc, ret, ringid);
-
+err:
         if (iov != iovstack)
                 kfree(iov);
         return ret;