block: fix buffer overflow when printing partition UUIDs

6d1d8050b4bc8 "block, partition: add partition_meta_info to hd_struct"
added part_unpack_uuid() which assumes that the passed in buffer has
enough space for sprintfing "%pU" - 37 characters including '\0'.

Unfortunately, b5af921ec0233 "init: add support for root devices
specified by partition UUID" supplied 33 bytes buffer to the function
leading to the following panic with stackprotector enabled.

  Kernel panic - not syncing: stack-protector: Kernel stack corrupted in: ffffffff81b14c7e

  [<ffffffff815e226b>] panic+0xba/0x1c6
  [<ffffffff81b14c7e>] ? printk_all_partitions+0x259/0x26xb
  [<ffffffff810566bb>] __stack_chk_fail+0x1b/0x20
  [<ffffffff81b15c7e>] printk_all_paritions+0x259/0x26xb
  [<ffffffff81aedfe0>] mount_block_root+0x1bc/0x27f
  [<ffffffff81aee0fa>] mount_root+0x57/0x5b
  [<ffffffff81aee23b>] prepare_namespace+0x13d/0x176
  [<ffffffff8107eec0>] ? release_tgcred.isra.4+0x330/0x30
  [<ffffffff81aedd60>] kernel_init+0x155/0x15a
  [<ffffffff81087b97>] ? schedule_tail+0x27/0xb0
  [<ffffffff815f4d24>] kernel_thread_helper+0x5/0x10
  [<ffffffff81aedc0b>] ? start_kernel+0x3c5/0x3c5
  [<ffffffff815f4d20>] ? gs_change+0x13/0x13

Increase the buffer size, remove the dangerous part_unpack_uuid() and
use snprintf() directly from printk_all_partitions().

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Szymon Gruszczynski <sz.gruszczynski@googlemail.com>
Cc: Will Drewry <wad@chromium.org>
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

2 files changed, 6 insertions, 10 deletions

diff --git a/block/genhd.c b/block/genhd.c
index df9816ede75b..9cf5583c90ff 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -743,7 +743,7 @@ void __init printk_all_partitions(void)
                 struct hd_struct *part;
                 char name_buf[BDEVNAME_SIZE];
                 char devt_buf[BDEVT_SIZE];
-                u8 uuid[PARTITION_META_INFO_UUIDLTH * 2 + 1];
+                char uuid_buf[PARTITION_META_INFO_UUIDLTH * 2 + 5];
 
                 /*
                  * Don't show empty devices or things that have been
@@ -762,14 +762,16 @@ void __init printk_all_partitions(void)
                 while ((part = disk_part_iter_next(&piter))) {
                         bool is_part0 = part == &disk->part0;
 
-                        uuid[0] = 0;
+                        uuid_buf[0] = '\0';
                         if (part->info)
-                                part_unpack_uuid(part->info->uuid, uuid);
+                                snprintf(uuid_buf, sizeof(uuid_buf), "%pU",
+                                         part->info->uuid);
 
                         printk("%s%s %10llu %s %s", is_part0 ? "" : "  ",
                                bdevt_str(part_devt(part), devt_buf),
                                (unsigned long long)part->nr_sects >> 1,
-                               disk_name(disk, part->partno, name_buf), uuid);
+                               disk_name(disk, part->partno, name_buf),
+                               uuid_buf);
                         if (is_part0) {
                                 if (disk->driverfs_dev != NULL &&
                                     disk->driverfs_dev->driver != NULL)
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index e61d3192448e..017a7fb5a1fc 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -222,12 +222,6 @@ static inline void part_pack_uuid(const u8 *uuid_str, u8 *to)
         }
 }
 
-static inline char *part_unpack_uuid(const u8 *uuid, char *out)
-{
-        sprintf(out, "%pU", uuid);
-        return out;
-}
-
 static inline int disk_max_parts(struct gendisk *disk)
 {
         if (disk->flags & GENHD_FL_EXT_DEVT)