[PATCH v2 04/14] sg_io: resolve conflicts between commands assigned to multiple classes (CVE-2012-4542)

[Paolo Bonzini <pbonzini@redhat.com>]

Some SCSI commands can be sent to disks via SG_IO even by unprivileged
users.  Unfortunately, some opcodes overlap across SCSI device classes
and have different meanings for different classes.  Four of them can
be used for read-only file descriptors on MMC, but should be limited to
descriptors opened for read-write on SBC:

The current bitmap of allowed commands is designed for MMC devices
(roughly, "play/burn CDs without requiring root").

- READ SUBCHANNEL <-> UNMAP (destructive, but no control on written
  data)

- GET PERFORMANCE <-> ERASE (not really a problem, no one supports
  ERASE anyway)

- READ DISC INFORMATION <-> XPWRITE (not commonly implemented but
  most dangerous)

- PLAY AUDIO TI <-> SANITIZE (a very new command)

To fix this, the series splits the bitmap entries for these four
commands into two entries, one read-only for MMC and one read-write
for the other device classes.

Cc: "James E.J. Bottomley" <JBottomley@parallels.com>
Cc: linux-scsi@vger.kernel.org
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 block/scsi_ioctl.c |   12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
index c4c42dd..7ea3428 100644
--- a/block/scsi_ioctl.c
+++ b/block/scsi_ioctl.c
@@ -182,29 +182,33 @@ static void blk_set_cmd_filter_defaults(struct blk_cmd_filter *filter)
 	sgio_bitmap_set(0x2E, D|      W|R|O|      B|K        , write); /* WRITE AND VERIFY(10) */
 	sgio_bitmap_set(0x35, D|      W|R|O|      B|K        , write); /* SYNCHRONIZE CACHE(10) */
 	sgio_bitmap_set(0x3F, D|      W|  O                  , write); /* WRITE LONG(10) */
+	sgio_bitmap_set(0x42, D                              , write); /* UNMAP */
+	sgio_bitmap_set(0x48, D|                  B          , write); /* SANITIZE */
+	sgio_bitmap_set(0x51, D                              , write); /* XPWRITE(10) */
 	sgio_bitmap_set(0x8A, D|T|    W|  O|      B          , write); /* WRITE(16) */
 	sgio_bitmap_set(0xAA, D|      W|R|O|              C  , write); /* WRITE(12) */
+	sgio_bitmap_set(0xAC,             O                  , write); /* ERASE(12) */
 	sgio_bitmap_set(0xAE, D|      W|  O                  , write); /* WRITE AND VERIFY(12) */
 	sgio_bitmap_set(0xEA, D|      W|  O                  , write); /* WRITE_LONG_2 ?? */
 
 	/* (mostly) MMC */
 
 	sgio_bitmap_set(0x23,           R                    , read);  /* READ FORMAT CAPACITIES */
-	sgio_bitmap_set(0x42, D|        R                    , read);  /* READ SUB-CHANNEL / UNMAP !! */
+	sgio_bitmap_set(0x42,           R                    , read);  /* READ SUB-CHANNEL */
 	sgio_bitmap_set(0x43,           R                    , read);  /* READ TOC/PMA/ATIP */
 	sgio_bitmap_set(0x44,   T|      R|            V      , read);  /* READ HEADER */
 	sgio_bitmap_set(0x45,           R                    , read);  /* PLAY AUDIO(10) */
 	sgio_bitmap_set(0x46,           R                    , read);  /* GET CONFIGURATION */
 	sgio_bitmap_set(0x47,           R                    , read);  /* PLAY AUDIO MSF */
-	sgio_bitmap_set(0x48, D|        R|        B          , read);  /* PLAY AUDIO TI / SANITIZE !! */
+	sgio_bitmap_set(0x48,           R                    , read);  /* PLAY AUDIO TI */
 	sgio_bitmap_set(0x4A,           R                    , read);  /* GET EVENT STATUS NOTIFICATION */
 	sgio_bitmap_set(0x4B,           R                    , read);  /* PAUSE/RESUME */
 	sgio_bitmap_set(0x4E,           R                    , read);  /* STOP PLAY/SCAN */
-	sgio_bitmap_set(0x51, D|        R                    , read);  /* READ DISC INFORMATION / XPWRITE(10) !! */
+	sgio_bitmap_set(0x51,           R                    , read);  /* READ DISC INFORMATION */
 	sgio_bitmap_set(0x52,           R                    , read);  /* READ TRACK INFORMATION */
 	sgio_bitmap_set(0x5C,           R                    , read);  /* READ BUFFER CAPACITY */
 	sgio_bitmap_set(0xA4,           R                    , read);  /* REPORT KEY */
-	sgio_bitmap_set(0xAC,           R|O                  , read);  /* GET PERFORMANCE / ERASE !! */
+	sgio_bitmap_set(0xAC,           R                    , read);  /* GET PERFORMANCE */
 	sgio_bitmap_set(0xAD,           R                    , read);  /* READ DVD STRUCTURE */
 	sgio_bitmap_set(0xB9,           R                    , read);  /* READ CD MSF */
 	sgio_bitmap_set(0xBA,           R                    , read);  /* SCAN */
-- 
1.7.1