[PATCH v4 0/2] Amiga RDB partition support fixes

[PATCH v4 0/2] Amiga RDB partition support fixes

[Michael Schmitz]

Jens,

as suggested, here's a new version of the Amiga RDB partition table
patch. I've split off the part fixing the incorrect use of signed int
for partition start address and size as separate patch. This change
should be incontroversial (I hope). It does fix the bug that Martin
Steigerwald reported six years ago for a 2 TB disk. I have tested this
patch with the identical RDB partition data that Martin saw the bug with.

The simple fix still leaves ample room for overflows in calculating start
address and size of a RDB partition, though such overflows should only be
seen in rather unusual cases. To address these potential overflows, checks
are added in the second patch of this series.

The use of u64 instead of sector_t in the second patch is required to catch
overflows even in cases where sector_t is 32 bit wide (i.e. no LBD support).

Cheers,

	Michael

[PATCH v4 1/2] block: fix signed int overflow in Amiga partition support

[Michael Schmitz]

The Amiga partition parser module uses signed int for partition sector
address and count, which will overflow for disks larger than 1 TB.

Use sector_t as type for sector address and size to allow using disks
up to 2 TB without LBD support, and disks larger than 2 TB with LBD.

This bug was reported originally in 2012, and the fix was created by
the RDB author, Joanne Dow <jdow@earthlink.net>. A patch had been
discussed and reviewed on linux-m68k at that time but never officially
submitted. This patch differs from Joanne's patch only in its use of
sector_t instead of unsigned int. No checking for overflows is done
(see patch 2 of this series for that).

Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=43511
Reported-by: Martin Steigerwald <Martin@lichtvoll.de>
Message-ID: <201206192146.09327.Martin@lichtvoll.de>
Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
Tested-by: Martin Steigerwald <Martin@lichtvoll.de>

---

Changes from v3:

- split off change of sector address type as quick fix.
- cast to sector_t in sector address calculations.
- move overflow checking to separate patch for more thorough review.
---
 block/partitions/amiga.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/block/partitions/amiga.c b/block/partitions/amiga.c
index 5609366..902ddeb 100644
--- a/block/partitions/amiga.c
+++ b/block/partitions/amiga.c
@@ -32,7 +32,8 @@ int amiga_partition(struct parsed_partitions *state)
 	unsigned char *data;
 	struct RigidDiskBlock *rdb;
 	struct PartitionBlock *pb;
-	int start_sect, nr_sects, blk, part, res = 0;
+	sector_t start_sect, nr_sects;
+	int blk, part, res = 0;
 	int blksize = 1;	/* Multiplier for disk block size */
 	int slot = 1;
 	char b[BDEVNAME_SIZE];
@@ -100,17 +101,17 @@ int amiga_partition(struct parsed_partitions *state)
 
 		/* Tell Kernel about it */
 
-		nr_sects = (be32_to_cpu(pb->pb_Environment[10]) + 1 -
-			    be32_to_cpu(pb->pb_Environment[9])) *
+		nr_sects = (sector_t) ((be32_to_cpu(pb->pb_Environment[10])
+			   + 1 - be32_to_cpu(pb->pb_Environment[9])) *
 			   be32_to_cpu(pb->pb_Environment[3]) *
 			   be32_to_cpu(pb->pb_Environment[5]) *
-			   blksize;
+			   blksize);
 		if (!nr_sects)
 			continue;
-		start_sect = be32_to_cpu(pb->pb_Environment[9]) *
+		start_sect = (sector_t) (be32_to_cpu(pb->pb_Environment[9]) *
 			     be32_to_cpu(pb->pb_Environment[3]) *
 			     be32_to_cpu(pb->pb_Environment[5]) *
-			     blksize;
+			     blksize);
 		put_partition(state,slot++,start_sect,nr_sects);
 		{
 			/* Be even more informative to aid mounting */
-- 
1.9.1

Re: [PATCH v4 1/2] block: fix signed int overflow in Amiga partition support

[Andreas Schwab]

On Sep 30 2018, Michael Schmitz <schmitzmic@gmail.com> wrote:

> @@ -100,17 +101,17 @@ int amiga_partition(struct parsed_partitions *state)
>  
>  		/* Tell Kernel about it */
>  
> -		nr_sects = (be32_to_cpu(pb->pb_Environment[10]) + 1 -
> -			    be32_to_cpu(pb->pb_Environment[9])) *
> +		nr_sects = (sector_t) ((be32_to_cpu(pb->pb_Environment[10])
> +			   + 1 - be32_to_cpu(pb->pb_Environment[9])) *
>  			   be32_to_cpu(pb->pb_Environment[3]) *
>  			   be32_to_cpu(pb->pb_Environment[5]) *
> -			   blksize;
> +			   blksize);

That doesn't fix any signed int overflow.  If you want to do calculation
in sector_t you need to cast at least one operand to sector_t.  In this
form the cast is useless.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

Re: [PATCH v4 1/2] block: fix signed int overflow in Amiga partition support

[Michael Schmitz]

Thanks Andreas,

it appears I already made the same error in v2 of this series. My bad.

I'll wait for a few more comments before respinning.

Cheers,

	Michael


Am 30.09.2018 um 19:16 schrieb Andreas Schwab:
> On Sep 30 2018, Michael Schmitz <schmitzmic@gmail.com> wrote:
>
>> @@ -100,17 +101,17 @@ int amiga_partition(struct parsed_partitions *state)
>>
>>  		/* Tell Kernel about it */
>>
>> -		nr_sects = (be32_to_cpu(pb->pb_Environment[10]) + 1 -
>> -			    be32_to_cpu(pb->pb_Environment[9])) *
>> +		nr_sects = (sector_t) ((be32_to_cpu(pb->pb_Environment[10])
>> +			   + 1 - be32_to_cpu(pb->pb_Environment[9])) *
>>  			   be32_to_cpu(pb->pb_Environment[3]) *
>>  			   be32_to_cpu(pb->pb_Environment[5]) *
>> -			   blksize;
>> +			   blksize);
>
> That doesn't fix any signed int overflow.  If you want to do calculation
> in sector_t you need to cast at least one operand to sector_t.  In this
> form the cast is useless.
>
> Andreas.
>

[PATCH v4 2/2] block: add overflow checks for Amiga partition support

[Michael Schmitz]

The Amiga partition parser module uses signed int for partition sector
address and count, which will overflow for disks larger than 1 TB.

Use u64 as type for sector address and size to allow using disks up to
2 TB without LBD support, and disks larger than 2 TB with LBD. The RBD
format allows to specify disk sizes up to 2^128 bytes (though native
OS limitations reduce this somewhat, to max 2^68 bytes), so check for
u64 overflow carefully to protect against overflowing sector_t.

Bail out if sector addresses overflow 32 bits on kernels without LBD
support.

This bug was reported originally in 2012, and the fix was created by
the RDB author, Joanne Dow <jdow@earthlink.net>. A patch had been
discussed and reviewed on linux-m68k at that time but never officially
submitted (now resubmitted as separate patch).
This patch adds additional error checking and warning messages.

Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=43511
Reported-by: Martin Steigerwald <Martin@lichtvoll.de>
Message-ID: <201206192146.09327.Martin@lichtvoll.de>
Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>

---

Changes from RFC:

- use u64 instead of sector_t, since that may be u32 without LBD support
- check multiplication overflows each step - 3 u32 values may exceed u64!
- warn against use on AmigaDOS if partition data overflow u32 sector count.
- warn if partition CylBlocks larger than what's stored in the RDSK header.
- bail out if we were to overflow sector_t (32 or 64 bit).

Changes from v1:

Kars de Jong:
- use defines for magic offsets in DosEnvec struct

Geert Uytterhoeven:
- use u64 cast for multiplications of u32 numbers
- use array3_size for overflow checks
- change pr_err to pr_warn
- discontinue use of pr_cont
- reword log messages
- drop redundant nr_sects overflow test
- warn against 32 bit overflow for each affected partition
- skip partitions that overflow sector_t size instead of aborting scan

Changes from v2:

- further trim 32 bit overflow test
- correct duplicate types.h inclusion introduced in v2

Changes from v3:

- split off sector address type fix for independent review
- change blksize to unsigned
- use check_mul_overflow() instead of array3_size()
- rewrite checks to avoid 64 bit divisions in check_mul_overflow()
---
 block/partitions/amiga.c | 86 +++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 74 insertions(+), 12 deletions(-)

diff --git a/block/partitions/amiga.c b/block/partitions/amiga.c
index 902ddeb..193e6c3 100644
--- a/block/partitions/amiga.c
+++ b/block/partitions/amiga.c
@@ -11,11 +11,19 @@
 #define pr_fmt(fmt) fmt
 
 #include <linux/types.h>
+#include <linux/mm_types.h>
+#include <linux/overflow.h>
 #include <linux/affs_hardblocks.h>
 
 #include "check.h"
 #include "amiga.h"
 
+/* magic offsets in partition DosEnvVec */
+#define NR_HD	3
+#define NR_SECT	5
+#define LO_CYL	9
+#define	HI_CYL	10
+
 static __inline__ u32
 checksum_block(__be32 *m, int size)
 {
@@ -32,9 +40,12 @@ int amiga_partition(struct parsed_partitions *state)
 	unsigned char *data;
 	struct RigidDiskBlock *rdb;
 	struct PartitionBlock *pb;
-	sector_t start_sect, nr_sects;
+	u64 start_sect, nr_sects;
+	sector_t end_sect;
+	u32 cylblk;		/* rdb_CylBlocks = nr_heads*sect_per_track */
+	u32 nr_hd, nr_sect, lo_cyl, hi_cyl;
 	int blk, part, res = 0;
-	int blksize = 1;	/* Multiplier for disk block size */
+	unsigned int blksize = 1;	/* Multiplier for disk block size */
 	int slot = 1;
 	char b[BDEVNAME_SIZE];
 
@@ -99,19 +110,70 @@ int amiga_partition(struct parsed_partitions *state)
 		if (checksum_block((__be32 *)pb, be32_to_cpu(pb->pb_SummedLongs) & 0x7F) != 0 )
 			continue;
 
-		/* Tell Kernel about it */
+		/* RDB gives us more than enough rope to hang ourselves with,
+		 * many times over (2^128 bytes if all fields max out).
+		 * Some careful checks are in order, so check for potential
+		 * overflows.
+		 * We are multiplying four 32 bit numbers to one sector_t!
+		 */
+
+		nr_hd   = be32_to_cpu(pb->pb_Environment[NR_HD]);
+		nr_sect = be32_to_cpu(pb->pb_Environment[NR_SECT]);
+
+		/* CylBlocks is total number of blocks per cylinder */
+		if (check_mul_overflow(nr_hd, nr_sect, &cylblk)) {
+			pr_err("Dev %s: heads*sects %u overflows u32, skipping partition!\n",
+				bdevname(state->bdev, b), cylblk);
+			continue;
+		}
+
+		/* check for consistency with RDB defined CylBlocks */
+		if (cylblk > be32_to_cpu(rdb->rdb_CylBlocks)) {
+			pr_warn("Dev %s: cylblk %u > rdb_CylBlocks %u!\n",
+				bdevname(state->bdev, b), cylblk,
+				be32_to_cpu(rdb->rdb_CylBlocks));
+		}
+
+		/* RDB allows for variable logical block size -
+		 * normalize to 512 byte blocks and check result.
+		 */
+
+		if (check_mul_overflow(cylblk, blksize, &cylblk)) {
+			pr_err("Dev %s: partition %u bytes per cyl. overflows u32, skipping partition!\n",
+				bdevname(state->bdev, b), part);
+			continue;
+		}
+
+		/* Calculate partition start and end. Limit of 32 bit on cylblk
+		 * guarantees no overflow occurs if LBD support is enabled.
+		 */
+
+		lo_cyl = be32_to_cpu(pb->pb_Environment[LO_CYL]);
+		start_sect = (u64) (lo_cyl * cylblk);
+
+		hi_cyl = be32_to_cpu(pb->pb_Environment[HI_CYL]);
+		nr_sects = (u64) ((hi_cyl - lo_cyl + 1) * cylblk);
 
-		nr_sects = (sector_t) ((be32_to_cpu(pb->pb_Environment[10])
-			   + 1 - be32_to_cpu(pb->pb_Environment[9])) *
-			   be32_to_cpu(pb->pb_Environment[3]) *
-			   be32_to_cpu(pb->pb_Environment[5]) *
-			   blksize);
 		if (!nr_sects)
 			continue;
-		start_sect = (sector_t) (be32_to_cpu(pb->pb_Environment[9]) *
-			     be32_to_cpu(pb->pb_Environment[3]) *
-			     be32_to_cpu(pb->pb_Environment[5]) *
-			     blksize);
+
+		/* Warn user if partition end overflows u32 (AmigaDOS limit) */
+
+		if ((start_sect + nr_sects) > UINT_MAX) {
+			pr_warn("Dev %s: partition %u (%llu-%llu) needs 64 bit device support!\n",
+				bdevname(state->bdev, b), part,
+				start_sect, start_sect + nr_sects);
+		}
+
+		if (check_add_overflow(start_sect, nr_sects, &end_sect)) {
+			pr_err("Dev %s: partition %u (%llu-%llu) needs LBD device support, skipping partition!\n",
+				bdevname(state->bdev, b), part,
+				start_sect, (u64) end_sect);
+			continue;
+		}
+
+		/* Tell Kernel about it */
+
 		put_partition(state,slot++,start_sect,nr_sects);
 		{
 			/* Be even more informative to aid mounting */
-- 
1.9.1