[PATCH v2] staging: lustre: llite: fix potential missing-check bug when copying lumv

From: Wenwen Wang
Date: Mon Apr 30 2018 - 18:56:44 EST

In ll_dir_ioctl(), the object lumv3 is firstly copied from the user space
using Its address, i.e., lumv1 = &lumv3. If the lmm_magic field of lumv3 is
LOV_USER_MAGIC_V3, lumv3 will be modified by the second copy from the user
space. The second copy is necessary, because the two versions (i.e.,
lov_user_md_v1 and lov_user_md_v3) have different data formats and lengths.
However, given that the user data resides in the user space, a malicious
user-space process can race to change the data between the two copies. By
doing so, the attacker can provide a data with an inconsistent version,
e.g., v1 version + v3 data. This can lead to logical errors in the
following execution in ll_dir_setstripe(), which performs different actions
according to the version specified by the field lmm_magic.

This patch rechecks the version field lmm_magic in the second copy. If the
version is not as expected, i.e., LOV_USER_MAGIC_V3, an error code will be
returned: -EINVAL.

Signed-off-by: Wenwen Wang <wang6495@xxxxxxx>
drivers/staging/lustre/lustre/llite/dir.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/staging/lustre/lustre/llite/dir.c b/drivers/staging/lustre/lustre/llite/dir.c
index d10d272..80d44ca 100644
--- a/drivers/staging/lustre/lustre/llite/dir.c
+++ b/drivers/staging/lustre/lustre/llite/dir.c
@@ -1185,6 +1185,8 @@ static long ll_dir_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
if (lumv1->lmm_magic == LOV_USER_MAGIC_V3) {
if (copy_from_user(&lumv3, lumv3p, sizeof(lumv3)))
return -EFAULT;
+ if (lumv3.lmm_magic != LOV_USER_MAGIC_V3)
+ return -EINVAL;

if (is_root_inode(inode))