openrisc: fix arbitrary kernel memory access via or1k_atomic syscallgrafted

sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user
pointers, v1 and v2, and swaps the words they point to in hand-written
assembly.

    l.lwz   r29,0(r4)
    l.lwz   r27,0(r5)
    l.sw    0(r4),r27
    l.sw    0(r5),r29

The pointers are not checked with access_ok(). The four memory
accesses also have no exception table entries.

A caller passes a kernel address as either pointer, and the syscall
reads from and writes to it directly.

This gives an unprivileged process a kernel read/write primitive. It
overwrites kernel data such as the sys_call_table, gaining code
execution in kernel context.

Check both pointers before entering the critical section. Add fixups
for the four memory accesses so faults on valid but unmapped user
addresses return -EFAULT.

[shorne@gmail.com: fix comment style]
Fixes: 9d02a4283e9c ("OpenRISC: Boot code")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 48 insertions, 0 deletions

diff --git a/block/partitions/ultrix.c b/block/partitions/ultrix.c
new file mode 100644
index 000000000..b4b9ddc57
--- /dev/null
+++ b/block/partitions/ultrix.c
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  fs/partitions/ultrix.c
+ *
+ *  Code extracted from drivers/block/genhd.c
+ *
+ *  Re-organised Jul 1999 Russell King
+ */
+
+#include "check.h"
+
+int ultrix_partition(struct parsed_partitions *state)
+{
+	int i;
+	Sector sect;
+	unsigned char *data;
+	struct ultrix_disklabel {
+		s32	pt_magic;	/* magic no. indicating part. info exits */
+		s32	pt_valid;	/* set by driver if pt is current */
+		struct  pt_info {
+			s32		pi_nblocks; /* no. of sectors */
+			u32		pi_blkoff;  /* block offset for start */
+		} pt_part[8];
+	} *label;
+
+#define PT_MAGIC	0x032957	/* Partition magic number */
+#define PT_VALID	1		/* Indicates if struct is valid */
+
+	data = read_part_sector(state, (16384 - sizeof(*label))/512, &sect);
+	if (!data)
+		return -1;
+	
+	label = (struct ultrix_disklabel *)(data + 512 - sizeof(*label));
+
+	if (label->pt_magic == PT_MAGIC && label->pt_valid == PT_VALID) {
+		for (i=0; i<8; i++)
+			if (label->pt_part[i].pi_nblocks)
+				put_partition(state, i+1, 
+					      label->pt_part[i].pi_blkoff,
+					      label->pt_part[i].pi_nblocks);
+		put_dev_sector(sect);
+		seq_buf_puts(&state->pp_buf, "\n");
+		return 1;
+	} else {
+		put_dev_sector(sect);
+		return 0;
+	}
+}