[Xen-changelog] [qemu-upstream-unstable] fdc: force the fifo access to be in bounds of the allocated buffer

[patchbot@xxxxxxx]

commit b2da824bc5ad35fb9f1e74a203d7be96a7b0345e
Author:     Petr Matousek <pmatouse@xxxxxxxxxx>
AuthorDate: Wed May 6 09:48:59 2015 +0200
Commit:     Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
CommitDate: Wed May 13 14:28:25 2015 +0000

    fdc: force the fifo access to be in bounds of the allocated buffer
    
    During processing of certain commands such as FD_CMD_READ_ID and
    FD_CMD_DRIVE_SPECIFICATION_COMMAND the fifo memory access could
    get out of bounds leading to memory corruption with values coming
    from the guest.
    
    Fix this by making sure that the index is always bounded by the
    allocated memory.
    
    This is CVE-2015-3456.
    
    Signed-off-by: Petr Matousek <pmatouse@xxxxxxxxxx>
    Reviewed-by: John Snow <jsnow@xxxxxxxxxx>
---
 hw/block/fdc.c |   17 +++++++++++------
 1 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/hw/block/fdc.c b/hw/block/fdc.c
index 739a03e..1168e8c 100644
--- a/hw/block/fdc.c
+++ b/hw/block/fdc.c
@@ -1512,7 +1512,7 @@ static uint32_t fdctrl_read_data(FDCtrl *fdctrl)
 {
     FDrive *cur_drv;
     uint32_t retval = 0;
-    int pos;
+    uint32_t pos;
 
     cur_drv = get_cur_drv(fdctrl);
     fdctrl->dsr &= ~FD_DSR_PWRDOWN;
@@ -1521,8 +1521,8 @@ static uint32_t fdctrl_read_data(FDCtrl *fdctrl)
         return 0;
     }
     pos = fdctrl->data_pos;
+    pos %= FD_SECTOR_LEN;
     if (fdctrl->msr & FD_MSR_NONDMA) {
-        pos %= FD_SECTOR_LEN;
         if (pos == 0) {
             if (fdctrl->data_pos != 0)
                 if (!fdctrl_seek_to_next_sect(fdctrl, cur_drv)) {
@@ -1867,10 +1867,13 @@ static void fdctrl_handle_option(FDCtrl *fdctrl, int 
direction)
 static void fdctrl_handle_drive_specification_command(FDCtrl *fdctrl, int 
direction)
 {
     FDrive *cur_drv = get_cur_drv(fdctrl);
+    uint32_t pos;
 
-    if (fdctrl->fifo[fdctrl->data_pos - 1] & 0x80) {
+    pos = fdctrl->data_pos - 1;
+    pos %= FD_SECTOR_LEN;
+    if (fdctrl->fifo[pos] & 0x80) {
         /* Command parameters done */
-        if (fdctrl->fifo[fdctrl->data_pos - 1] & 0x40) {
+        if (fdctrl->fifo[pos] & 0x40) {
             fdctrl->fifo[0] = fdctrl->fifo[1];
             fdctrl->fifo[2] = 0;
             fdctrl->fifo[3] = 0;
@@ -1970,7 +1973,7 @@ static uint8_t command_to_handler[256];
 static void fdctrl_write_data(FDCtrl *fdctrl, uint32_t value)
 {
     FDrive *cur_drv;
-    int pos;
+    uint32_t pos;
 
     /* Reset mode */
     if (!(fdctrl->dor & FD_DOR_nRESET)) {
@@ -2019,7 +2022,9 @@ static void fdctrl_write_data(FDCtrl *fdctrl, uint32_t 
value)
     }
 
     FLOPPY_DPRINTF("%s: %02x\n", __func__, value);
-    fdctrl->fifo[fdctrl->data_pos++] = value;
+    pos = fdctrl->data_pos++;
+    pos %= FD_SECTOR_LEN;
+    fdctrl->fifo[pos] = value;
     if (fdctrl->data_pos == fdctrl->data_len) {
         /* We now have all parameters
          * and will be able to treat the command
--
generated by git-patchbot for /home/xen/git/qemu-upstream-unstable.git

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