ide: Check array bounds before writing to io_buffer (CVE-2015-5154)

If the end_transfer_func of a command is called because enough data has
been read or written for the current PIO transfer, and it fails to
correctly call the command completion functions, the DRQ bit in the
status register and s->end_transfer_func may remain set. This allows the
guest to access further bytes in s->io_buffer beyond s->data_end, and
eventually overflowing the io_buffer.

One case where this currently happens is emulation of the ATAPI command
START STOP UNIT.

This patch fixes the problem by adding explicit array bounds checks
before accessing the buffer instead of relying on end_transfer_func to
function correctly.

[ This is XSA-138 / CVE-2015-5154. ]

Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/hw/ide.c b/hw/ide.c
index 791666b898732bcd08b83e84f3f27d78886deb9e..211ec88588a4488a7d8f9a1de66ce7b08c75ea9a 100644 (file)
--- a/hw/ide.c
+++ b/hw/ide.c
@@ -3002,6 +3002,10 @@ static void ide_data_writew(void *opaque, uint32_t addr, uint32_t val)
     buffered_pio_write(s, addr, 2);
 
     p = s->data_ptr;
+    if (p + 2 > s->data_end) {
+        return;
+    }
+
     *(uint16_t *)p = le16_to_cpu(val);
     p += 2;
     s->data_ptr = p;
@@ -3021,6 +3025,10 @@ static uint32_t ide_data_readw(void *opaque, uint32_t addr)
     buffered_pio_read(s, addr, 2);
 
     p = s->data_ptr;
+    if (p + 2 > s->data_end) {
+        return 0;
+    }
+
     ret = cpu_to_le16(*(uint16_t *)p);
     p += 2;
     s->data_ptr = p;
@@ -3040,6 +3048,10 @@ static void ide_data_writel(void *opaque, uint32_t addr, uint32_t val)
     buffered_pio_write(s, addr, 4);
 
     p = s->data_ptr;
+    if (p + 4 > s->data_end) {
+        return;
+    }
+
     *(uint32_t *)p = le32_to_cpu(val);
     p += 4;
     s->data_ptr = p;
@@ -3059,6 +3071,10 @@ static uint32_t ide_data_readl(void *opaque, uint32_t addr)
     buffered_pio_read(s, addr, 4);
 
     p = s->data_ptr;
+    if (p + 4 > s->data_end) {
+        return 0;
+    }
+
     ret = cpu_to_le32(*(uint32_t *)p);
     p += 4;
     s->data_ptr = p;