On pSeries, when user attempts to use the same vfio container used by different iommu group, the spapr_tce_set_window() returns -EPERM and the subsequent cleanup leads to the below crash.

Kernel attempted to read user page (308) - exploit attempt? BUG: Kernel NULL pointer dereference on read at 0x00000308 Faulting instruction address: 0xc0000000001ce358 Oops: Kernel access of bad area, sig: 11 [#1] NIP: c0000000001ce358 LR: c0000000001ce05c CTR: c00000000005add0 <snip> NIP [c0000000001ce358] spapr_tce_unset_window+0x3b8/0x510 LR [c0000000001ce05c] spapr_tce_unset_window+0xbc/0x510 Call Trace: spapr_tce_unset_window+0xbc/0x510 (unreliable) tce_iommu_attach_group+0x24c/0x340 [vfio_iommu_spapr_tce] vfio_container_attach_group+0xec/0x240 [vfio] vfio_group_fops_unl_ioctl+0x548/0xb00 [vfio] sys_ioctl+0x754/0x1580 system_call_exception+0x13c/0x330 system_call_vectored_common+0x15c/0x2ec <snip> --- interrupt: 3000

Fix this by having null check for the tbl passed to the spapr_tce_unset_window().

Fixes: f431a8cde7f1 ("powerpc/iommu: Reimplement the iommu_table_group_ops for pSeries") Cc: stable@vger.kernel.org Reported-by: Vaishnavi Bhat vaish123@in.ibm.com Signed-off-by: Shivaprasad G Bhat sbhat@linux.ibm.com --- arch/powerpc/platforms/pseries/iommu.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c index 534cd159e9ab..78b895b568b3 100644 --- a/arch/powerpc/platforms/pseries/iommu.c +++ b/arch/powerpc/platforms/pseries/iommu.c @@ -2205,6 +2205,9 @@ static long spapr_tce_unset_window(struct iommu_table_group *table_group, int nu const char *win_name; int ret = -ENODEV;

+ if (!tbl) /* The table was never created OR window was never opened */ + return 0; + mutex_lock(&dma_win_init_mutex);

if ((num == 0) && is_default_window_table(table_group, tbl))