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@xxxxxxxxxxxxxxx
Reported-by: Vaishnavi Bhat <vaish123@xxxxxxxxxx>
Signed-off-by: Shivaprasad G Bhat <sbhat@xxxxxxxxxxxxx>
---
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))
