libxc: check return values from malloc

A sufficiently malformed input to libxc (such as a malformed input ELF
or other guest-controlled data) might cause one of libxc's malloc() to
fail.  In this case we need to make sure we don't dereference or do
pointer arithmetic on the result.

Search for all occurrences of \b(m|c|re)alloc in libxc, and all
functions which call them, and add appropriate error checking where
missing.

This includes the functions xc_dom_malloc*, which now print a message
when they fail so that callers don't have to do so.

The function xc_cpuid_to_str wasn't provided with a sane return value
and has a pretty strange API, which now becomes a little stranger.
There are no in-tree callers.

Changes in the Xen 4.2 version of this series:
* No need to fix code relating to ARM.
* No need to fix code relating to superpage support.
* Additionally fix `dom->p2m_host = xc_dom_malloc...' in xc_dom_ia64.c.

Changes in the Xen 4.1 version of this series:
* An additional check is needed in xc_flask.c:xc_flask_access.

This is part of the fix to a security issue, XSA-55.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>

10 files changed, 56 insertions, 3 deletions

diff --git a/tools/libxc/xc_cpuid_x86.c b/tools/libxc/xc_cpuid_x86.c
index f61308a196..5adf2d9fca 100644
--- a/tools/libxc/xc_cpuid_x86.c
+++ b/tools/libxc/xc_cpuid_x86.c
@@ -515,6 +515,8 @@ static int xc_cpuid_do_domctl(
 static char *alloc_str(void)
 {
     char *s = malloc(33);
+    if ( s == NULL )
+        return s;
     memset(s, 0, 33);
     return s;
 }
@@ -526,6 +528,8 @@ void xc_cpuid_to_str(const unsigned int *regs, char **strs)
     for ( i = 0; i < 4; i++ )
     {
         strs[i] = alloc_str();
+        if ( strs[i] == NULL )
+            continue;
         for ( j = 0; j < 32; j++ )
             strs[i][j] = !!((regs[i] & (1U << (31 - j)))) ? '1' : '0';
     }
@@ -599,7 +603,7 @@ int xc_cpuid_check(
     const char **config,
     char **config_transformed)
 {
-    int i, j;
+    int i, j, rc;
     unsigned int regs[4];
 
     memset(config_transformed, 0, 4 * sizeof(*config_transformed));
@@ -611,6 +615,11 @@ int xc_cpuid_check(
         if ( config[i] == NULL )
             continue;
         config_transformed[i] = alloc_str();
+        if ( config_transformed[i] == NULL )
+        {
+            rc = -ENOMEM;
+            goto fail_rc;
+        }
         for ( j = 0; j < 32; j++ )
         {
             unsigned char val = !!((regs[i] & (1U << (31 - j))));
@@ -627,12 +636,14 @@ int xc_cpuid_check(
     return 0;
 
  fail:
+    rc = -EPERM;
+ fail_rc:
     for ( i = 0; i < 4; i++ )
     {
         free(config_transformed[i]);
         config_transformed[i] = NULL;
     }
-    return -EPERM;
+    return rc;
 }
 
 /*
@@ -677,6 +688,11 @@ int xc_cpuid_set(
         }
         
         config_transformed[i] = alloc_str();
+        if ( config_transformed[i] == NULL )
+        {
+            rc = -ENOMEM;
+            goto fail;
+        }
 
         for ( j = 0; j < 32; j++ )
         {
diff --git a/tools/libxc/xc_dom_core.c b/tools/libxc/xc_dom_core.c
index a54ddae3d3..3cbf9f791e 100644
--- a/tools/libxc/xc_dom_core.c
+++ b/tools/libxc/xc_dom_core.c
@@ -120,9 +120,17 @@ void *xc_dom_malloc(struct xc_dom_image *dom, size_t size)
 {
     struct xc_dom_mem *block;
 
+    if ( size > SIZE_MAX - sizeof(*block) )
+    {
+        DOMPRINTF("%s: unreasonable allocation size", __FUNCTION__);
+        return NULL;
+    }
     block = malloc(sizeof(*block) + size);
     if ( block == NULL )
+    {
+        DOMPRINTF("%s: allocation failed", __FUNCTION__);
         return NULL;
+    }
     memset(block, 0, sizeof(*block) + size);
     block->next = dom->memblocks;
     dom->memblocks = block;
@@ -138,7 +146,10 @@ void *xc_dom_malloc_page_aligned(struct xc_dom_image *dom, size_t size)
 
     block = malloc(sizeof(*block));
     if ( block == NULL )
+    {
+        DOMPRINTF("%s: allocation failed", __FUNCTION__);
         return NULL;
+    }
     memset(block, 0, sizeof(*block));
     block->mmap_len = size;
     block->mmap_ptr = mmap(NULL, block->mmap_len,
@@ -146,6 +157,7 @@ void *xc_dom_malloc_page_aligned(struct xc_dom_image *dom, size_t size)
                            -1, 0);
     if ( block->mmap_ptr == MAP_FAILED )
     {
+        DOMPRINTF("%s: mmap failed", __FUNCTION__);
         free(block);
         return NULL;
     }
@@ -202,6 +214,7 @@ void *xc_dom_malloc_filemap(struct xc_dom_image *dom,
         close(fd);
     if ( block != NULL )
         free(block);
+    DOMPRINTF("%s: failed (on file `%s')", __FUNCTION__, filename);
     return NULL;
 }
 
diff --git a/tools/libxc/xc_dom_elfloader.c b/tools/libxc/xc_dom_elfloader.c
index aa6b5f0546..0fb3629e59 100644
--- a/tools/libxc/xc_dom_elfloader.c
+++ b/tools/libxc/xc_dom_elfloader.c
@@ -329,6 +329,8 @@ static elf_errorstatus xc_dom_parse_elf_kernel(struct xc_dom_image *dom)
         return rc;
 
     elf = xc_dom_malloc(dom, sizeof(*elf));
+    if ( elf == NULL )
+        return -1;
     dom->private_loader = elf;
     rc = elf_init(elf, dom->kernel_blob, dom->kernel_size);
     xc_elf_set_logfile(dom->xch, elf, 1);
diff --git a/tools/libxc/xc_dom_ia64.c b/tools/libxc/xc_dom_ia64.c
index 7c0eff15d8..076821c19d 100644
--- a/tools/libxc/xc_dom_ia64.c
+++ b/tools/libxc/xc_dom_ia64.c
@@ -188,6 +188,12 @@ int arch_setup_meminit(struct xc_dom_image *dom)
 
     /* setup initial p2m */
     dom->p2m_host = xc_dom_malloc(dom, sizeof(xen_pfn_t) * nbr);
+    if ( dom->p2m_host == NULL )
+    {
+        DOMPRINTF("%s: xc_dom_malloc failed for p2m_host",
+                  __FUNCTION__);
+        return -1;
+    }
     for ( pfn = 0; pfn < nbr; pfn++ )
         dom->p2m_host[pfn] = start + pfn;
 
diff --git a/tools/libxc/xc_dom_x86.c b/tools/libxc/xc_dom_x86.c
index 75d6b8336c..448d9a1e74 100644
--- a/tools/libxc/xc_dom_x86.c
+++ b/tools/libxc/xc_dom_x86.c
@@ -780,6 +780,9 @@ int arch_setup_meminit(struct xc_dom_image *dom)
     }
 
     dom->p2m_host = xc_dom_malloc(dom, sizeof(xen_pfn_t) * dom->total_pages);
+    if ( dom->p2m_host == NULL )
+        return -EINVAL;
+
     if ( dom->superpages )
     {
         int count = dom->total_pages >> SUPERPAGE_PFN_SHIFT;
diff --git a/tools/libxc/xc_domain_restore.c b/tools/libxc/xc_domain_restore.c
index 29af52bac6..0f1e2d16c1 100644
--- a/tools/libxc/xc_domain_restore.c
+++ b/tools/libxc/xc_domain_restore.c
@@ -967,6 +967,11 @@ static int apply_batch(xc_interface *xch, uint32_t dom, struct restore_ctx *ctx,
 
     /* Map relevant mfns */
     pfn_err = calloc(j, sizeof(*pfn_err));
+    if ( pfn_err == NULL )
+    {
+        PERROR("allocation for pfn_err failed");
+        return -1;
+    }
     region_base = xc_map_foreign_bulk(
         xch, dom, PROT_WRITE, region_mfn, pfn_err, j);
 
diff --git a/tools/libxc/xc_flask.c b/tools/libxc/xc_flask.c
index 27794a82d5..78c243c9e0 100644
--- a/tools/libxc/xc_flask.c
+++ b/tools/libxc/xc_flask.c
@@ -284,6 +284,8 @@ int xc_flask_access(xc_interface *xc_handle, const char *scon, const char *tcon,
         MAX_SHORT_DEC_LEN + 1 +
         sizeof(req)*2 + 1;
     buf = malloc(bufLen);
+    if ( buf == NULL )
+        return -ENOMEM;
     snprintf(buf, bufLen, "%s %s %hu %x", scon, tcon, tclass, req);
 
     op.cmd = FLASK_ACCESS;
diff --git a/tools/libxc/xc_linux_osdep.c b/tools/libxc/xc_linux_osdep.c
index 6477ad8607..fa7bb7c14c 100644
--- a/tools/libxc/xc_linux_osdep.c
+++ b/tools/libxc/xc_linux_osdep.c
@@ -294,6 +294,8 @@ static void *linux_privcmd_map_foreign_range(xc_interface *xch, xc_osdep_handle
 
     num = (size + XC_PAGE_SIZE - 1) >> XC_PAGE_SHIFT;
     arr = calloc(num, sizeof(xen_pfn_t));
+    if ( arr == NULL )
+        return NULL;
 
     for ( i = 0; i < num; i++ )
         arr[i] = mfn + i;
@@ -318,6 +320,8 @@ static void *linux_privcmd_map_foreign_ranges(xc_interface *xch, xc_osdep_handle
     num_per_entry = chunksize >> XC_PAGE_SHIFT;
     num = num_per_entry * nentries;
     arr = calloc(num, sizeof(xen_pfn_t));
+    if ( arr == NULL )
+        return NULL;
 
     for ( i = 0; i < nentries; i++ )
         for ( j = 0; j < num_per_entry; j++ )
diff --git a/tools/libxc/xc_private.c b/tools/libxc/xc_private.c
index 09c8f23ca5..1bf25d2a1e 100644
--- a/tools/libxc/xc_private.c
+++ b/tools/libxc/xc_private.c
@@ -742,6 +742,8 @@ const char *xc_strerror(xc_interface *xch, int errcode)
         errbuf = pthread_getspecific(errbuf_pkey);
         if (errbuf == NULL) {
             errbuf = malloc(XS_BUFSIZE);
+            if ( errbuf == NULL )
+                return "(failed to allocate errbuf)";
             pthread_setspecific(errbuf_pkey, errbuf);
         }
 
diff --git a/tools/libxc/xenctrl.h b/tools/libxc/xenctrl.h
index 570c6d46b5..9bc9172376 100644
--- a/tools/libxc/xenctrl.h
+++ b/tools/libxc/xenctrl.h
@@ -1608,7 +1608,7 @@ int xc_cpuid_set(xc_interface *xch,
 int xc_cpuid_apply_policy(xc_interface *xch,
                           domid_t domid);
 void xc_cpuid_to_str(const unsigned int *regs,
-                     char **strs);
+                     char **strs); /* some strs[] may be NULL if ENOMEM */
 int xc_mca_op(xc_interface *xch, struct xen_mc *mc);
 #endif