On Sun, Apr 29, 2018 at 8:20 AM, Greg Kroah-Hartman <gre...@linuxfoundation.org> wrote: > On Sat, Apr 28, 2018 at 04:04:25PM +0000, Dilger, Andreas wrote: >> On Apr 27, 2018, at 17:45, Wenwen Wang <wang6...@umn.edu> wrote: >> > [PATCH] staging: luster: llite: fix potential missing-check bug when >> > copying lumv >> >> (typo) s/luster/lustre/ >> >> > 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_MAGIV_V3, lumv3 will be modified by the second copy from the user >> >> (typo) s/MAGIV/MAGIC/ >> >> > 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 isn't a serious bug in the end. The LOV_USER_MAGIC_V3 check just copies >> a bit more data from userspace (the lmm_pool field). It would be more of a >> problem if the reverse was possible (copy smaller V1 buffer, but change the >> magic to LOV_USER_MAGIC_V3 afterward), but this isn't possible since the >> second >> copy is not done if there is a V1 magic. If the user changes from V3 magic >> to V1 in a racy manner it means less data will be used than copied, which >> is harmless. >> >> > 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. >> >> This isn't a bad idea in any case, since it verifies the data copied from >> userspace is still valid. > > So you agree with this patch? Or do not? > > confused, > > greg k-h
It is worth fixing this bug, since it offers an opportunity for adversaries to provide inconsistent user data. In addition to the unwanted version LOV_USER_MAGIC_V1, a malicious user can also use the version LMV_USER_MAGIC, which is also unexpected but allowed in the function ll_dir_setstripe(). These inconsistent data can cause potential logical errors in the following execution. Hence it is necessary to re-verify the data copied from userspace. Thanks! Wenwen
