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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen-4.2-testing] libxc: builder: limit maximum size of kernel/ramdisk.
# HG changeset patch
# User Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
# Date 1351264255 -3600
# Node ID 537776f51f79c5789d06f97b363596a197c3e71c
# Parent 40ccbee890e1fc053de3046bbc3d13b8ff6f5d63
libxc: builder: limit maximum size of kernel/ramdisk.
Allowing user supplied kernels of arbitrary sizes, especially during
decompression, can swallow up dom0 memory leading to either virtual
address space exhaustion in the builder process or allocation
failures/OOM killing of both toolstack and unrelated processes.
We disable these checks when building in a stub domain for pvgrub
since this uses the guest's own memory and is isolated.
Decompression of gzip compressed kernels and ramdisks has been safe
since 14954:58205257517d (Xen 3.1.0 onwards).
This is XSA-25 / CVE-2012-4544.
Also make explicit checks for buffer overflows in various
decompression routines. These were already ruled out due to other
properties of the code but check them as a belt-and-braces measure.
Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---
diff -r 40ccbee890e1 -r 537776f51f79 stubdom/grub/kexec.c
--- a/stubdom/grub/kexec.c Thu Oct 25 15:36:32 2012 +0200
+++ b/stubdom/grub/kexec.c Fri Oct 26 16:10:55 2012 +0100
@@ -137,6 +137,10 @@ void kexec(void *kernel, long kernel_siz
dom = xc_dom_allocate(xc_handle, cmdline, features);
dom->allocate = kexec_allocate;
+ /* We are using guest owned memory, therefore no limits. */
+ xc_dom_kernel_max_size(dom, 0);
+ xc_dom_ramdisk_max_size(dom, 0);
+
dom->kernel_blob = kernel;
dom->kernel_size = kernel_size;
diff -r 40ccbee890e1 -r 537776f51f79 tools/libxc/xc_dom.h
--- a/tools/libxc/xc_dom.h Thu Oct 25 15:36:32 2012 +0200
+++ b/tools/libxc/xc_dom.h Fri Oct 26 16:10:55 2012 +0100
@@ -55,6 +55,9 @@ struct xc_dom_image {
void *ramdisk_blob;
size_t ramdisk_size;
+ size_t max_kernel_size;
+ size_t max_ramdisk_size;
+
/* arguments and parameters */
char *cmdline;
uint32_t f_requested[XENFEAT_NR_SUBMAPS];
@@ -180,6 +183,23 @@ void xc_dom_release_phys(struct xc_dom_i
void xc_dom_release(struct xc_dom_image *dom);
int xc_dom_mem_init(struct xc_dom_image *dom, unsigned int mem_mb);
+/* Set this larger if you have enormous ramdisks/kernels. Note that
+ * you should trust all kernels not to be maliciously large (e.g. to
+ * exhaust all dom0 memory) if you do this (see CVE-2012-4544 /
+ * XSA-25). You can also set the default independently for
+ * ramdisks/kernels in xc_dom_allocate() or call
+ * xc_dom_{kernel,ramdisk}_max_size.
+ */
+#ifndef XC_DOM_DECOMPRESS_MAX
+#define XC_DOM_DECOMPRESS_MAX (1024*1024*1024) /* 1GB */
+#endif
+
+int xc_dom_kernel_check_size(struct xc_dom_image *dom, size_t sz);
+int xc_dom_kernel_max_size(struct xc_dom_image *dom, size_t sz);
+
+int xc_dom_ramdisk_check_size(struct xc_dom_image *dom, size_t sz);
+int xc_dom_ramdisk_max_size(struct xc_dom_image *dom, size_t sz);
+
size_t xc_dom_check_gzip(xc_interface *xch,
void *blob, size_t ziplen);
int xc_dom_do_gunzip(xc_interface *xch,
@@ -240,7 +260,8 @@ void xc_dom_log_memory_footprint(struct
void *xc_dom_malloc(struct xc_dom_image *dom, size_t size);
void *xc_dom_malloc_page_aligned(struct xc_dom_image *dom, size_t size);
void *xc_dom_malloc_filemap(struct xc_dom_image *dom,
- const char *filename, size_t * size);
+ const char *filename, size_t * size,
+ const size_t max_size);
char *xc_dom_strdup(struct xc_dom_image *dom, const char *str);
/* --- alloc memory pool ------------------------------------------- */
diff -r 40ccbee890e1 -r 537776f51f79 tools/libxc/xc_dom_bzimageloader.c
--- a/tools/libxc/xc_dom_bzimageloader.c Thu Oct 25 15:36:32 2012 +0200
+++ b/tools/libxc/xc_dom_bzimageloader.c Fri Oct 26 16:10:55 2012 +0100
@@ -47,13 +47,19 @@ static int xc_try_bzip2_decode(
char *out_buf;
char *tmp_buf;
int retval = -1;
- int outsize;
+ unsigned int outsize;
uint64_t total;
stream.bzalloc = NULL;
stream.bzfree = NULL;
stream.opaque = NULL;
+ if ( dom->kernel_size == 0)
+ {
+ DOMPRINTF("BZIP2: Input is 0 size");
+ return -1;
+ }
+
ret = BZ2_bzDecompressInit(&stream, 0, 0);
if ( ret != BZ_OK )
{
@@ -66,6 +72,17 @@ static int xc_try_bzip2_decode(
* the input buffer to start, and we'll realloc as needed.
*/
outsize = dom->kernel_size;
+
+ /*
+ * stream.avail_in and outsize are unsigned int, while kernel_size
+ * is a size_t. Check we aren't overflowing.
+ */
+ if ( outsize != dom->kernel_size )
+ {
+ DOMPRINTF("BZIP2: Input too large");
+ goto bzip2_cleanup;
+ }
+
out_buf = malloc(outsize);
if ( out_buf == NULL )
{
@@ -98,13 +115,20 @@ static int xc_try_bzip2_decode(
if ( stream.avail_out == 0 )
{
/* Protect against output buffer overflow */
- if ( outsize > INT_MAX / 2 )
+ if ( outsize > UINT_MAX / 2 )
{
DOMPRINTF("BZIP2: output buffer overflow");
free(out_buf);
goto bzip2_cleanup;
}
+ if ( xc_dom_kernel_check_size(dom, outsize * 2) )
+ {
+ DOMPRINTF("BZIP2: output too large");
+ free(out_buf);
+ goto bzip2_cleanup;
+ }
+
tmp_buf = realloc(out_buf, outsize * 2);
if ( tmp_buf == NULL )
{
@@ -172,9 +196,15 @@ static int _xc_try_lzma_decode(
unsigned char *out_buf;
unsigned char *tmp_buf;
int retval = -1;
- int outsize;
+ size_t outsize;
const char *msg;
+ if ( dom->kernel_size == 0)
+ {
+ DOMPRINTF("%s: Input is 0 size", what);
+ return -1;
+ }
+
/* sigh. We don't know up-front how much memory we are going to need
* for the output buffer. Allocate the output buffer to be equal
* the input buffer to start, and we'll realloc as needed.
@@ -244,13 +274,20 @@ static int _xc_try_lzma_decode(
if ( stream->avail_out == 0 )
{
/* Protect against output buffer overflow */
- if ( outsize > INT_MAX / 2 )
+ if ( outsize > SIZE_MAX / 2 )
{
DOMPRINTF("%s: output buffer overflow", what);
free(out_buf);
goto lzma_cleanup;
}
+ if ( xc_dom_kernel_check_size(dom, outsize * 2) )
+ {
+ DOMPRINTF("%s: output too large", what);
+ free(out_buf);
+ goto lzma_cleanup;
+ }
+
tmp_buf = realloc(out_buf, outsize * 2);
if ( tmp_buf == NULL )
{
@@ -359,6 +396,12 @@ static int xc_try_lzo1x_decode(
0x89, 0x4c, 0x5a, 0x4f, 0x00, 0x0d, 0x0a, 0x1a, 0x0a
};
+ /*
+ * lzo_uint should match size_t. Check that this is the case to be
+ * sure we won't overflow various lzo_uint fields.
+ */
+ XC_BUILD_BUG_ON(sizeof(lzo_uint) != sizeof(size_t));
+
ret = lzo_init();
if ( ret != LZO_E_OK )
{
@@ -438,6 +481,14 @@ static int xc_try_lzo1x_decode(
if ( src_len <= 0 || src_len > dst_len || src_len > left )
break;
+ msg = "Output buffer overflow";
+ if ( *size > SIZE_MAX - dst_len )
+ break;
+
+ msg = "Decompressed image too large";
+ if ( xc_dom_kernel_check_size(dom, *size + dst_len) )
+ break;
+
msg = "Failed to (re)alloc memory";
tmp_buf = realloc(out_buf, *size + dst_len);
if ( tmp_buf == NULL )
diff -r 40ccbee890e1 -r 537776f51f79 tools/libxc/xc_dom_core.c
--- a/tools/libxc/xc_dom_core.c Thu Oct 25 15:36:32 2012 +0200
+++ b/tools/libxc/xc_dom_core.c Fri Oct 26 16:10:55 2012 +0100
@@ -159,7 +159,8 @@ void *xc_dom_malloc_page_aligned(struct
}
void *xc_dom_malloc_filemap(struct xc_dom_image *dom,
- const char *filename, size_t * size)
+ const char *filename, size_t * size,
+ const size_t max_size)
{
struct xc_dom_mem *block = NULL;
int fd = -1;
@@ -171,6 +172,13 @@ void *xc_dom_malloc_filemap(struct xc_do
lseek(fd, 0, SEEK_SET);
*size = lseek(fd, 0, SEEK_END);
+ if ( max_size && *size > max_size )
+ {
+ xc_dom_panic(dom->xch, XC_OUT_OF_MEMORY,
+ "tried to map file which is too large");
+ goto err;
+ }
+
block = malloc(sizeof(*block));
if ( block == NULL )
goto err;
@@ -222,6 +230,40 @@ char *xc_dom_strdup(struct xc_dom_image
}
/* ------------------------------------------------------------------------ */
+/* decompression buffer sizing */
+int xc_dom_kernel_check_size(struct xc_dom_image *dom, size_t sz)
+{
+ /* No limit */
+ if ( !dom->max_kernel_size )
+ return 0;
+
+ if ( sz > dom->max_kernel_size )
+ {
+ xc_dom_panic(dom->xch, XC_INVALID_KERNEL,
+ "kernel image too large");
+ return 1;
+ }
+
+ return 0;
+}
+
+int xc_dom_ramdisk_check_size(struct xc_dom_image *dom, size_t sz)
+{
+ /* No limit */
+ if ( !dom->max_ramdisk_size )
+ return 0;
+
+ if ( sz > dom->max_ramdisk_size )
+ {
+ xc_dom_panic(dom->xch, XC_INVALID_KERNEL,
+ "ramdisk image too large");
+ return 1;
+ }
+
+ return 0;
+}
+
+/* ------------------------------------------------------------------------ */
/* read files, copy memory blocks, with transparent gunzip */
size_t xc_dom_check_gzip(xc_interface *xch, void *blob, size_t ziplen)
@@ -235,7 +277,7 @@ size_t xc_dom_check_gzip(xc_interface *x
gzlen = blob + ziplen - 4;
unziplen = gzlen[3] << 24 | gzlen[2] << 16 | gzlen[1] << 8 | gzlen[0];
- if ( (unziplen < 0) || (unziplen > (1024*1024*1024)) ) /* 1GB limit */
+ if ( (unziplen < 0) || (unziplen > XC_DOM_DECOMPRESS_MAX) )
{
xc_dom_printf
(xch,
@@ -288,6 +330,9 @@ int xc_dom_try_gunzip(struct xc_dom_imag
if ( unziplen == 0 )
return 0;
+ if ( xc_dom_kernel_check_size(dom, unziplen) )
+ return 0;
+
unzip = xc_dom_malloc(dom, unziplen);
if ( unzip == NULL )
return -1;
@@ -588,6 +633,9 @@ struct xc_dom_image *xc_dom_allocate(xc_
memset(dom, 0, sizeof(*dom));
dom->xch = xch;
+ dom->max_kernel_size = XC_DOM_DECOMPRESS_MAX;
+ dom->max_ramdisk_size = XC_DOM_DECOMPRESS_MAX;
+
if ( cmdline )
dom->cmdline = xc_dom_strdup(dom, cmdline);
if ( features )
@@ -608,10 +656,25 @@ struct xc_dom_image *xc_dom_allocate(xc_
return NULL;
}
+int xc_dom_kernel_max_size(struct xc_dom_image *dom, size_t sz)
+{
+ DOMPRINTF("%s: kernel_max_size=%zx", __FUNCTION__, sz);
+ dom->max_kernel_size = sz;
+ return 0;
+}
+
+int xc_dom_ramdisk_max_size(struct xc_dom_image *dom, size_t sz)
+{
+ DOMPRINTF("%s: ramdisk_max_size=%zx", __FUNCTION__, sz);
+ dom->max_ramdisk_size = sz;
+ return 0;
+}
+
int xc_dom_kernel_file(struct xc_dom_image *dom, const char *filename)
{
DOMPRINTF("%s: filename=\"%s\"", __FUNCTION__, filename);
- dom->kernel_blob = xc_dom_malloc_filemap(dom, filename, &dom->kernel_size);
+ dom->kernel_blob = xc_dom_malloc_filemap(dom, filename, &dom->kernel_size,
+ dom->max_kernel_size);
if ( dom->kernel_blob == NULL )
return -1;
return xc_dom_try_gunzip(dom, &dom->kernel_blob, &dom->kernel_size);
@@ -621,7 +684,9 @@ int xc_dom_ramdisk_file(struct xc_dom_im
{
DOMPRINTF("%s: filename=\"%s\"", __FUNCTION__, filename);
dom->ramdisk_blob =
- xc_dom_malloc_filemap(dom, filename, &dom->ramdisk_size);
+ xc_dom_malloc_filemap(dom, filename, &dom->ramdisk_size,
+ dom->max_ramdisk_size);
+
if ( dom->ramdisk_blob == NULL )
return -1;
// return xc_dom_try_gunzip(dom, &dom->ramdisk_blob, &dom->ramdisk_size);
@@ -781,7 +846,11 @@ int xc_dom_build_image(struct xc_dom_ima
void *ramdiskmap;
unziplen = xc_dom_check_gzip(dom->xch, dom->ramdisk_blob,
dom->ramdisk_size);
+ if ( xc_dom_ramdisk_check_size(dom, unziplen) != 0 )
+ unziplen = 0;
+
ramdisklen = unziplen ? unziplen : dom->ramdisk_size;
+
if ( xc_dom_alloc_segment(dom, &dom->ramdisk_seg, "ramdisk", 0,
ramdisklen) != 0 )
goto err;
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