[Xen-changelog] [xen-3.4-testing] libxc: [CVE-2011-1583] pv kernel image validation

[Xen patchbot-3.4-testing <patchbot@xxxxxxx>]

# HG changeset patch
# User Keith Coleman <keith.coleman@xxxxxxxxxxxxx>
# Date 1314686158 14400
# Node ID 60b3ca4d973af88dbdb380c5d4b21a0a961459f5
# Parent  3b39c0fd26a6ee25e953ea0f2852c1253bd94c51
libxc: [CVE-2011-1583] pv kernel image validation

The functions which interpret the kernel image supplied for a
paravirtualised guest, and decompress it into memory when booting the
domain, are incautious. Specifically:

(i) Integer overflow in the decompression loop memory allocator might
result in overrunning the buffer used for the decompressed image;
(ii) Integer overflows and lack of checking of certain length fields
can result in the loader reading its own address space beyond the
size of the supplied kernel image file.
(iii) Lack of error checking in the decompression loop can lead to an
infinite loop.

This patch fixes these problems.

CVE-2011-1583.

Signed-off-by: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Committed-by: Keith Coleman <keith.coleman@xxxxxxxxxxxxx>
---


diff -r 3b39c0fd26a6 -r 60b3ca4d973a tools/libxc/xc_dom_bzimageloader.c
--- a/tools/libxc/xc_dom_bzimageloader.c        Mon May 09 03:06:33 2011 -0400
+++ b/tools/libxc/xc_dom_bzimageloader.c        Tue Aug 30 02:35:58 2011 -0400
@@ -68,8 +68,29 @@
     for ( ; ; )
     {
         ret = BZ2_bzDecompress(&stream);
-        if ( (stream.avail_out == 0) || (ret != BZ_OK) )
+        if ( ret == BZ_STREAM_END )
         {
+            xc_dom_printf("BZIP2: Saw data stream end\n");
+            retval = 0;
+            break;
+        }
+        if ( ret != BZ_OK )
+        {
+            xc_dom_printf("BZIP2: error %d", ret);
+            free(out_buf);
+            goto bzip2_cleanup;
+        }
+
+        if ( stream.avail_out == 0 )
+        {
+            /* Protect against output buffer overflow */
+            if ( outsize > INT_MAX / 2 )
+            {
+                xc_dom_printf("BZIP2: output buffer overflow\n");
+                free(out_buf);
+                goto bzip2_cleanup;
+            }
+
             tmp_buf = realloc(out_buf, outsize * 2);
             if ( tmp_buf == NULL )
             {
@@ -83,16 +104,18 @@
             stream.avail_out = (outsize * 2) - outsize;
             outsize *= 2;
         }
-
-        if ( ret != BZ_OK )
+        else if ( stream.avail_in == 0 )
         {
-            if ( ret == BZ_STREAM_END )
-            {
-                xc_dom_printf("BZIP2: Saw data stream end\n");
-                retval = 0;
-                break;
-            }
-            xc_dom_printf("BZIP2: error\n");
+            /*
+             * If there is output buffer available then this indicates
+             * that BZ2_bzDecompress would like more input data to be
+             * provided.  However our complete input buffer is in
+             * memory and provided upfront so if avail_in is zero this
+             * actually indicates a truncated input.
+             */
+            xc_dom_printf("BZIP2: not enough input\n");
+            free(out_buf);
+            goto bzip2_cleanup;
         }
     }
 
@@ -187,31 +210,14 @@
     for ( ; ; )
     {
         ret = lzma_code(&stream, action);
-        if ( (stream.avail_out == 0) || (ret != LZMA_OK) )
+        if ( ret == LZMA_STREAM_END )
         {
-            tmp_buf = realloc(out_buf, outsize * 2);
-            if ( tmp_buf == NULL )
-            {
-                xc_dom_printf("LZMA: Failed to realloc memory\n");
-                free(out_buf);
-                goto lzma_cleanup;
-            }
-            out_buf = tmp_buf;
-
-            stream.next_out = out_buf + outsize;
-            stream.avail_out = (outsize * 2) - outsize;
-            outsize *= 2;
+            xc_dom_printf("LZMA: Saw data stream end\n");
+            retval = 0;
+            break;
         }
-
         if ( ret != LZMA_OK )
         {
-            if ( ret == LZMA_STREAM_END )
-            {
-                xc_dom_printf("LZMA: Saw data stream end\n");
-                retval = 0;
-                break;
-            }
-
             switch ( ret )
             {
             case LZMA_MEM_ERROR:
@@ -245,7 +251,32 @@
             }
             xc_dom_printf("%s: LZMA decompression error %s\n",
                           __FUNCTION__, msg);
-            break;
+            free(out_buf);
+            goto lzma_cleanup;
+        }
+
+        if ( stream.avail_out == 0 )
+        {
+            /* Protect against output buffer overflow */
+            if ( outsize > INT_MAX / 2 )
+            {
+                xc_dom_printf("LZMA: output buffer overflow\n");
+                free(out_buf);
+                goto lzma_cleanup;
+            }
+
+            tmp_buf = realloc(out_buf, outsize * 2);
+            if ( tmp_buf == NULL )
+            {
+                xc_dom_printf("LZMA: Failed to realloc memory");
+                free(out_buf);
+                goto lzma_cleanup;
+            }
+            out_buf = tmp_buf;
+
+            stream.next_out = out_buf + outsize;
+            stream.avail_out = (outsize * 2) - outsize;
+            outsize *= 2;
         }
     }
 
@@ -314,18 +345,18 @@
 
 extern struct xc_dom_loader elf_loader;
 
-static unsigned int payload_offset(struct setup_header *hdr)
+static int check_magic(struct xc_dom_image *dom, const void *magic, size_t len)
 {
-    unsigned int off;
+    if (len > dom->kernel_size)
+        return 0;
 
-    off = (hdr->setup_sects + 1) * 512;
-    off += hdr->payload_offset;
-    return off;
+    return (memcmp(dom->kernel_blob, magic, len) == 0);
 }
 
 static int xc_dom_probe_bzimage_kernel(struct xc_dom_image *dom)
 {
     struct setup_header *hdr;
+    uint64_t payload_offset, payload_length;
     int ret;
 
     if ( dom->kernel_blob == NULL )
@@ -358,10 +389,30 @@
         return -EINVAL;
     }
 
-    dom->kernel_blob = dom->kernel_blob + payload_offset(hdr);
-    dom->kernel_size = hdr->payload_length;
 
-    if ( memcmp(dom->kernel_blob, "\037\213", 2) == 0 )
+    /* upcast to 64 bits to avoid overflow */
+    /* setup_sects is u8 and so cannot overflow */
+    payload_offset = (hdr->setup_sects + 1) * 512;
+    payload_offset += hdr->payload_offset;
+    payload_length = hdr->payload_length;
+
+    if ( payload_offset >= dom->kernel_size )
+    {
+        xc_dom_panic(XC_INVALID_KERNEL, "%s: payload offset overflow",
+                     __FUNCTION__);
+        return -EINVAL;
+    }
+    if ( (payload_offset + payload_length) > dom->kernel_size )
+    {
+        xc_dom_panic(XC_INVALID_KERNEL, "%s: payload length overflow",
+                     __FUNCTION__);
+        return -EINVAL;
+    }
+
+    dom->kernel_blob = dom->kernel_blob + payload_offset;
+    dom->kernel_size = payload_length;
+
+    if ( check_magic(dom, "\037\213", 2) )
     {
         ret = xc_dom_try_gunzip(dom, &dom->kernel_blob, &dom->kernel_size);
         if ( ret == -1 )
@@ -372,7 +423,7 @@
             return -EINVAL;
         }
     }
-    else if ( memcmp(dom->kernel_blob, "\102\132\150", 3) == 0 )
+    else if ( check_magic(dom, "\102\132\150", 3) )
     {
         ret = xc_try_bzip2_decode(dom, &dom->kernel_blob, &dom->kernel_size);
         if ( ret < 0 )
@@ -383,7 +434,7 @@
             return -EINVAL;
         }
     }
-    else if ( memcmp(dom->kernel_blob, "\135\000", 2) == 0 )
+    else if ( check_magic(dom, "\135\000", 2) )
     {
         ret = xc_try_lzma_decode(dom, &dom->kernel_blob, &dom->kernel_size);
         if ( ret < 0 )

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