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.

upstream-commit-id: d2ff85854512574e7209f295e87b0835d5b032c6

Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

diff --git a/hw/ide/core.c b/hw/ide/core.c
index 3fe67caeac1f8b7f2de444cd437aa57082fe30d6..3c4b32eb7d268bc7d6730688df479f25b27e21eb 100644 (file)
--- a/hw/ide/core.c
+++ b/hw/ide/core.c
@@ -1900,6 +1900,10 @@ void ide_data_writew(void *opaque, uint32_t addr, uint32_t val)
     }
 
     p = s->data_ptr;
+    if (p + 2 > s->data_end) {
+        return;
+    }
+
     *(uint16_t *)p = le16_to_cpu(val);
     p += 2;
     s->data_ptr = p;
@@ -1921,6 +1925,10 @@ uint32_t ide_data_readw(void *opaque, uint32_t addr)
     }
 
     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;
@@ -1942,6 +1950,10 @@ void ide_data_writel(void *opaque, uint32_t addr, uint32_t val)
     }
 
     p = s->data_ptr;
+    if (p + 4 > s->data_end) {
+        return;
+    }
+
     *(uint32_t *)p = le32_to_cpu(val);
     p += 4;
     s->data_ptr = p;
@@ -1963,6 +1975,10 @@ uint32_t ide_data_readl(void *opaque, uint32_t addr)
     }
 
     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;