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, 87 insertions, 0 deletions

diff --git a/block/partitions/osf.c b/block/partitions/osf.c
new file mode 100644
index 000000000..2a692584d
--- /dev/null
+++ b/block/partitions/osf.c
@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  fs/partitions/osf.c
+ *
+ *  Code extracted from drivers/block/genhd.c
+ *
+ *  Copyright (C) 1991-1998  Linus Torvalds
+ *  Re-organised Feb 1998 Russell King
+ */
+
+#include "check.h"
+
+#define MAX_OSF_PARTITIONS 18
+#define DISKLABELMAGIC (0x82564557UL)
+
+int osf_partition(struct parsed_partitions *state)
+{
+	int i;
+	int slot = 1;
+	unsigned int npartitions;
+	Sector sect;
+	unsigned char *data;
+	struct disklabel {
+		__le32 d_magic;
+		__le16 d_type,d_subtype;
+		u8 d_typename[16];
+		u8 d_packname[16];
+		__le32 d_secsize;
+		__le32 d_nsectors;
+		__le32 d_ntracks;
+		__le32 d_ncylinders;
+		__le32 d_secpercyl;
+		__le32 d_secprtunit;
+		__le16 d_sparespertrack;
+		__le16 d_sparespercyl;
+		__le32 d_acylinders;
+		__le16 d_rpm, d_interleave, d_trackskew, d_cylskew;
+		__le32 d_headswitch, d_trkseek, d_flags;
+		__le32 d_drivedata[5];
+		__le32 d_spare[5];
+		__le32 d_magic2;
+		__le16 d_checksum;
+		__le16 d_npartitions;
+		__le32 d_bbsize, d_sbsize;
+		struct d_partition {
+			__le32 p_size;
+			__le32 p_offset;
+			__le32 p_fsize;
+			u8  p_fstype;
+			u8  p_frag;
+			__le16 p_cpg;
+		} d_partitions[MAX_OSF_PARTITIONS];
+	} * label;
+	struct d_partition * partition;
+
+	data = read_part_sector(state, 0, &sect);
+	if (!data)
+		return -1;
+
+	label = (struct disklabel *) (data+64);
+	partition = label->d_partitions;
+	if (le32_to_cpu(label->d_magic) != DISKLABELMAGIC) {
+		put_dev_sector(sect);
+		return 0;
+	}
+	if (le32_to_cpu(label->d_magic2) != DISKLABELMAGIC) {
+		put_dev_sector(sect);
+		return 0;
+	}
+	npartitions = le16_to_cpu(label->d_npartitions);
+	if (npartitions > MAX_OSF_PARTITIONS) {
+		put_dev_sector(sect);
+		return 0;
+	}
+	for (i = 0 ; i < npartitions; i++, partition++) {
+		if (slot == state->limit)
+		        break;
+		if (le32_to_cpu(partition->p_size))
+			put_partition(state, slot,
+				le32_to_cpu(partition->p_offset),
+				le32_to_cpu(partition->p_size));
+		slot++;
+	}
+	seq_buf_puts(&state->pp_buf, "\n");
+	put_dev_sector(sect);
+	return 1;
+}