partitions/efi: Fix integer overflow in GPT size calculation

If a GUID Partition Table claims to have more than 2**25 entries, the
calculation of the partition table size in alloc_read_gpt_entries() will
overflow a 32-bit integer and not enough space will be allocated for the
table.

Nothing seems to get written out of bounds, but later efi_partition() will
read up to 32768 bytes from a 128 byte buffer, possibly OOPSing or exposing
information to /proc/partitions and uevents.

The problem exists on both 64-bit and 32-bit platforms.

Fix the overflow and also print a meaningful debug message if the table
size is too large.

Signed-off-by: Alden Tondettar <alden.tondettar@gmail.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 12 insertions, 5 deletions

diff --git a/block/partitions/efi.c b/block/partitions/efi.c
index bcd86e5cd546..39f70d968754 100644
--- a/block/partitions/efi.c
+++ b/block/partitions/efi.c
@@ -293,7 +293,7 @@ static gpt_entry *alloc_read_gpt_entries(struct parsed_partitions *state,
         if (!gpt)
                 return NULL;
 
-        count = le32_to_cpu(gpt->num_partition_entries) *
+        count = (size_t)le32_to_cpu(gpt->num_partition_entries) *
                 le32_to_cpu(gpt->sizeof_partition_entry);
         if (!count)
                 return NULL;
@@ -352,7 +352,7 @@ static int is_gpt_valid(struct parsed_partitions *state, u64 lba,
                         gpt_header **gpt, gpt_entry **ptes)
 {
         u32 crc, origcrc;
-        u64 lastlba;
+        u64 lastlba, pt_size;
 
         if (!ptes)
                 return 0;
@@ -434,13 +434,20 @@ static int is_gpt_valid(struct parsed_partitions *state, u64 lba,
                 goto fail;
         }
 
+        /* Sanity check partition table size */
+        pt_size = (u64)le32_to_cpu((*gpt)->num_partition_entries) *
+                le32_to_cpu((*gpt)->sizeof_partition_entry);
+        if (pt_size > KMALLOC_MAX_SIZE) {
+                pr_debug("GUID Partition Table is too large: %llu > %lu bytes\n",
+                         (unsigned long long)pt_size, KMALLOC_MAX_SIZE);
+                goto fail;
+        }
+
         if (!(*ptes = alloc_read_gpt_entries(state, *gpt)))
                 goto fail;
 
         /* Check the GUID Partition Entry Array CRC */
-        crc = efi_crc32((const unsigned char *) (*ptes),
-                        le32_to_cpu((*gpt)->num_partition_entries) *
-                        le32_to_cpu((*gpt)->sizeof_partition_entry));
+        crc = efi_crc32((const unsigned char *) (*ptes), pt_size);
 
         if (crc != le32_to_cpu((*gpt)->partition_entry_array_crc32)) {
                 pr_debug("GUID Partition Entry Array CRC check failed.\n");