[PATCH] scsi: esas2r: fix possible buffer overflow caused by bad DMA value in esas2r_process_fs_ioctl()

[Jia-Ju Bai]

In esas2r_read_fs():
  struct esas2r_ioctl_fs *fs = 
         (struct esas2r_ioctl_fs *)a->fs_api_buffer;

Because "a->fs_api_buffer" is mapped to coherent DMA (allocated in
esas2r_write_fs()), "fs" is also mapped to DMA.

Then esas2r_read_fs() calls esas2r_process_fs_ioctl() with "fs".

In esas2r_process_fs_ioctl():
  fsc = &fs->command;
  ...
  if (fsc->command >= cmdcnt) {
    fs->status = ATTO_STS_INV_FUNC;
    return false;
  }
  func = cmd_to_fls_func[fsc->command];
  if (func == 0xFF) {
    fs->status = ATTO_STS_INV_FUNC;
    return false;
  }

Because "fs" is mapped to DMA, its data can be modified at anytime by
malicious or malfunctioning hardware. In this case, the check 
"if (fsc->command >= cmdcnt)" can be passed, and then "fsc->command" 
can be modified by hardware to cause buffer overflow.

To fix this problem, "fsc->command" is assigned to a local variable, and
then this local variable is used to replace "fsc->command".

Signed-off-by: Jia-Ju Bai <baiji...@tsinghua.edu.cn>
---
 drivers/scsi/esas2r/esas2r_flash.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/esas2r/esas2r_flash.c 
b/drivers/scsi/esas2r/esas2r_flash.c
index b02ac389e6c6..ca5ff0d4c7d0 100644
--- a/drivers/scsi/esas2r/esas2r_flash.c
+++ b/drivers/scsi/esas2r/esas2r_flash.c
@@ -851,6 +851,7 @@ bool esas2r_process_fs_ioctl(struct esas2r_adapter *a,
        struct esas2r_ioctlfs_command *fsc = &fs->command;
        u8 func = 0;
        u32 datalen;
+       u8 command = fsc->command;
 
        fs->status = ATTO_STS_FAILED;
        fs->driver_error = RS_PENDING;
@@ -860,18 +861,18 @@ bool esas2r_process_fs_ioctl(struct esas2r_adapter *a,
                return false;
        }
 
-       if (fsc->command >= cmdcnt) {
+       if (command >= cmdcnt) {
                fs->status = ATTO_STS_INV_FUNC;
                return false;
        }
 
-       func = cmd_to_fls_func[fsc->command];
+       func = cmd_to_fls_func[command];
        if (func == 0xFF) {
                fs->status = ATTO_STS_INV_FUNC;
                return false;
        }
 
-       if (fsc->command != ESAS2R_FS_CMD_CANCEL) {
+       if (command != ESAS2R_FS_CMD_CANCEL) {
                if ((a->pcid->device != ATTO_DID_MV_88RC9580
                     || fs->adap_type != ESAS2R_FS_AT_ESASRAID2)
                    && (a->pcid->device != ATTO_DID_MV_88RC9580TS
-- 
2.17.1