[PATCH v2] ide: atapi: check logical block address and read size (CVE-2020-29443)

[P J P]

From: Prasad J Pandit <pjp@fedoraproject.org>

While processing ATAPI cmd_read/cmd_read_cd commands,
Logical Block Address (LBA) maybe invalid OR closer to the last block,
leading to an OOB access issues. Add range check to avoid it.

Fixes: CVE-2020-29443
Reported-by: Wenxiang Qian <leonwxqian@gmail.com>
Fix-suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 hw/ide/atapi.c | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

Update v2: range check lba value early in cmd_read[_cd] routines
  -> https://lists.gnu.org/archive/html/qemu-devel/2020-12/msg00151.html

diff --git a/hw/ide/atapi.c b/hw/ide/atapi.c
index e79157863f..35b8494dc8 100644
--- a/hw/ide/atapi.c
+++ b/hw/ide/atapi.c
@@ -322,6 +322,8 @@ static void ide_atapi_cmd_reply(IDEState *s, int size, int 
max_size)
 static void ide_atapi_cmd_read_pio(IDEState *s, int lba, int nb_sectors,
                                    int sector_size)
 {
+    assert (0 <= lba && lba < (s->nb_sectors >> 2));
+
     s->lba = lba;
     s->packet_transfer_size = nb_sectors * sector_size;
     s->elementary_transfer_size = 0;
@@ -420,6 +422,8 @@ eot:
 static void ide_atapi_cmd_read_dma(IDEState *s, int lba, int nb_sectors,
                                    int sector_size)
 {
+    assert (0 <= lba && lba < (s->nb_sectors >> 2));
+
     s->lba = lba;
     s->packet_transfer_size = nb_sectors * sector_size;
     s->io_buffer_size = 0;
@@ -973,35 +977,49 @@ static void cmd_prevent_allow_medium_removal(IDEState *s, 
uint8_t* buf)

 static void cmd_read(IDEState *s, uint8_t* buf)
 {
-    int nb_sectors, lba;
+    unsigned int nb_sectors, lba;
+
+    /* Total logical sectors of ATAPI_SECTOR_SIZE(=2048) bytes */
+    uint64_t total_sectors = s->nb_sectors >> 2;

     if (buf[0] == GPCMD_READ_10) {
         nb_sectors = lduw_be_p(buf + 7);
     } else {
         nb_sectors = ldl_be_p(buf + 6);
     }
-
-    lba = ldl_be_p(buf + 2);
     if (nb_sectors == 0) {
         ide_atapi_cmd_ok(s);
         return;
     }

+    lba = ldl_be_p(buf + 2);
+    if (lba >= total_sectors || lba + nb_sectors - 1 >= total_sectors) {
+        ide_atapi_cmd_error(s, ILLEGAL_REQUEST, ASC_LOGICAL_BLOCK_OOR);
+        return;
+    }
+
     ide_atapi_cmd_read(s, lba, nb_sectors, 2048);
 }

 static void cmd_read_cd(IDEState *s, uint8_t* buf)
 {
-    int nb_sectors, lba, transfer_request;
+    unsigned int nb_sectors, lba, transfer_request;
+
+    /* Total logical sectors of ATAPI_SECTOR_SIZE(=2048) bytes */
+    uint64_t total_sectors = s->nb_sectors >> 2;

     nb_sectors = (buf[6] << 16) | (buf[7] << 8) | buf[8];
-    lba = ldl_be_p(buf + 2);
-
     if (nb_sectors == 0) {
         ide_atapi_cmd_ok(s);
         return;
     }

+    lba = ldl_be_p(buf + 2);
+    if (lba >= total_sectors || lba + nb_sectors - 1 >= total_sectors) {
+        ide_atapi_cmd_error(s, ILLEGAL_REQUEST, ASC_LOGICAL_BLOCK_OOR);
+        return;
+    }
+
     transfer_request = buf[9] & 0xf8;
     if (transfer_request == 0x00) {
         /* nothing */
--
2.29.2