3.16.63-rc1 review patch. If anyone has any objections, please let me know.
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From: Wenwen Wang wang6495@umn.edu
commit 800a7340ab7dd667edf95e74d8e4f23a17e87076 upstream.
In copy_params(), the struct 'dm_ioctl' is first copied from the user space buffer 'user' to 'param_kernel' and the field 'data_size' is checked against 'minimum_data_size' (size of 'struct dm_ioctl' payload up to its 'data' member). If the check fails, an error code EINVAL will be returned. Otherwise, param_kernel->data_size is used to do a second copy, which copies from the same user-space buffer to 'dmi'. After the second copy, only 'dmi->data_size' is checked against 'param_kernel->data_size'. Given that the buffer 'user' resides in the user space, a malicious user-space process can race to change the content in the buffer between the two copies. This way, the attacker can inject inconsistent data into 'dmi' (versus previously validated 'param_kernel').
Fix redundant copying of 'minimum_data_size' from user-space buffer by using the first copy stored in 'param_kernel'. Also remove the 'data_size' check after the second copy because it is now unnecessary.
Signed-off-by: Wenwen Wang wang6495@umn.edu Signed-off-by: Mike Snitzer snitzer@redhat.com Signed-off-by: Ben Hutchings ben@decadent.org.uk --- drivers/md/dm-ioctl.c | 18 ++++++------------ 1 file changed, 6 insertions(+), 12 deletions(-)
--- a/drivers/md/dm-ioctl.c +++ b/drivers/md/dm-ioctl.c @@ -1681,8 +1681,7 @@ static void free_params(struct dm_ioctl }
static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl *param_kernel, - int ioctl_flags, - struct dm_ioctl **param, int *param_flags) + int ioctl_flags, struct dm_ioctl **param, int *param_flags) { struct dm_ioctl *dmi; int secure_data; @@ -1730,18 +1729,13 @@ static int copy_params(struct dm_ioctl _ return -ENOMEM; }
- if (copy_from_user(dmi, user, param_kernel->data_size)) - goto bad; + /* Copy from param_kernel (which was already copied from user) */ + memcpy(dmi, param_kernel, minimum_data_size);
-data_copied: - /* - * Abort if something changed the ioctl data while it was being copied. - */ - if (dmi->data_size != param_kernel->data_size) { - DMERR("rejecting ioctl: data size modified while processing parameters"); + if (copy_from_user(&dmi->data, (char __user *)user + minimum_data_size, + param_kernel->data_size - minimum_data_size)) goto bad; - } - +data_copied: /* Wipe the user buffer so we do not return it to userspace */ if (secure_data && clear_user(user, param_kernel->data_size)) goto bad;