Fix corrupted OSF partition table parsing

The kernel automatically evaluates partition tables of storage devices.
The code for evaluating OSF partitions contains a bug that leaks data
from kernel heap memory to userspace for certain corrupted OSF
partitions.

In more detail:

  for (i = 0 ; i < le16_to_cpu(label->d_npartitions); i++, partition++) {

iterates from 0 to d_npartitions - 1, where d_npartitions is read from
the partition table without validation and partition is a pointer to an
array of at most 8 d_partitions.

Add the proper and obvious validation.

Signed-off-by: Timo Warns <warns@pre-sense.de>
Cc: stable@kernel.org
[ Changed the patch trivially to not repeat the whole le16_to_cpu()
  thing, and to use an explicit constant for the magic value '8' ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 2 deletions

diff --git a/fs/partitions/osf.c b/fs/partitions/osf.c
index 48cec7cbca17..be03a0b08b47 100644
--- a/fs/partitions/osf.c
+++ b/fs/partitions/osf.c
@@ -10,10 +10,13 @@
 #include "check.h"
 #include "osf.h"
 
+#define MAX_OSF_PARTITIONS 8
+
 int osf_partition(struct parsed_partitions *state)
 {
         int i;
         int slot = 1;
+        unsigned int npartitions;
         Sector sect;
         unsigned char *data;
         struct disklabel {
@@ -45,7 +48,7 @@ int osf_partition(struct parsed_partitions *state)
                         u8  p_fstype;
                         u8  p_frag;
                         __le16 p_cpg;
-                } d_partitions[8];
+                } d_partitions[MAX_OSF_PARTITIONS];
         } * label;
         struct d_partition * partition;
 
@@ -63,7 +66,12 @@ int osf_partition(struct parsed_partitions *state)
                 put_dev_sector(sect);
                 return 0;
         }
-        for (i = 0 ; i < le16_to_cpu(label->d_npartitions); i++, partition++) {
+        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))