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>

diff --git a/fs/compat.c b/fs/compat.c
index fe40fde..d487985 100644 (file)
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -558,6 +558,10 @@ ssize_t compat_rw_copy_check_uvector(int type,
        }
        *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
@@ -1080,17 +1084,12 @@ static ssize_t compat_do_readv_writev(int type, struct file *file,
        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;

diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
index 926b466..fd26d04 100644 (file)
--- a/mm/process_vm_access.c
+++ b/mm/process_vm_access.c
@@ -429,12 +429,6 @@ 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,
@@ -459,8 +453,6 @@ free_iovecs:
                kfree(iov_r);
        if (iov_l != iovstack_l)
                kfree(iov_l);
-
-out:
        return rc;
 }
 

diff --git a/security/keys/compat.c b/security/keys/compat.c
index 1c26176..d65fa7f 100644 (file)
--- 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;