[ 43/49] Fix: compat_rw_copy_check_uvector() misuse in aio, readv, writev, and security keys

Greg Kroah-Hartman
2013-03-26T23:06:47Z

From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

commit 8aec0f5d4137532de14e6554fd5dd201ff3a3c49 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/compat.c | 15 +++++++--------
security/keys/compat.c | 4 ++--
2 files changed, 9 insertions(+), 10 deletions(-)

--- a/fs/compat.c
+++ b/fs/compat.c
@@ -576,6 +576,10 @@ ssize_t compat_rw_copy_check_uvector(int
}
*ret_pointer = iov;

+ ret = -EFAULT;
+ if (!access_ok(VERIFY_READ, uvector, nr_segs*sizeof(*uvector)))
+ goto out;
+
/*
* Single unix specification:
* We should -EINVAL if an element length is not >= 0 and fitting an
@@ -1106,17 +1110,12 @@ static ssize_t compat_do_readv_writev(in
if (!file->f_op)
goto out;

- ret = -EFAULT;
- if (!access_ok(VERIFY_READ, uvector, nr_segs*sizeof(*uvector)))
- goto out;
-
- tot_len = compat_rw_copy_check_uvector(type, uvector, nr_segs,
+ ret = compat_rw_copy_check_uvector(type, uvector, nr_segs,
UIO_FASTIOV, iovstack, &iov);
- if (tot_len == 0) {
- ret = 0;
+ if (ret <= 0)
goto out;
- }

+ tot_len = ret;
ret = rw_verify_area(type, file, pos, tot_len);
if (ret < 0)
goto out;
--- a/security/keys/compat.c
+++ b/security/keys/compat.c
@@ -40,12 +40,12 @@ 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;