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

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>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

1 files changed, 0 insertions, 8 deletions

diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
index e920aa3ce104..70e814a4d0b8 100644
--- a/mm/process_vm_access.c
+++ b/mm/process_vm_access.c
@@ -434,12 +434,6 @@ compat_process_vm_rw(compat_pid_t pid,
 	if (flags != 0)
 		return -EINVAL;
 
-	if (!access_ok(VERIFY_READ, lvec, liovcnt * sizeof(*lvec)))
-		goto out;
-
-	if (!access_ok(VERIFY_READ, rvec, riovcnt * sizeof(*rvec)))
-		goto out;
-
 	if (vm_write)
 		rc = compat_rw_copy_check_uvector(WRITE, lvec, liovcnt,
 						  UIO_FASTIOV, iovstack_l,
@@ -464,8 +458,6 @@ free_iovecs:
 		kfree(iov_r);
 	if (iov_l != iovstack_l)
 		kfree(iov_l);
-
-out:
 	return rc;
 }