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.

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

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

9 files changed, 54 insertions, 3 deletions

diff --git a/tools/libxc/xc_cpuid_x86.c b/tools/libxc/xc_cpuid_x86.c
index 0882ce6554..da435ce513 100644
--- a/tools/libxc/xc_cpuid_x86.c
+++ b/tools/libxc/xc_cpuid_x86.c
@@ -589,6 +589,8 @@ 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;
 }
@@ -600,6 +602,8 @@ 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';
     }
@@ -680,7 +684,7 @@ 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));
@@ -692,6 +696,11 @@ 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))));
@@ -708,12 +717,14 @@ 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;
 }
 
 /*
@@ -758,6 +769,11 @@ 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 61b57987ee..be582761d1 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 3994f8fd55..f9ed6b2170 100644
--- a/tools/libxc/xc_domain_restore.c
+++ b/tools/libxc/xc_domain_restore.c
@@ -1180,6 +1180,11 @@ 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_linux_osdep.c b/tools/libxc/xc_linux_osdep.c
index 787e74285e..98e041cd9f 100644
--- a/tools/libxc/xc_linux_osdep.c
+++ b/tools/libxc/xc_linux_osdep.c
@@ -378,6 +378,8 @@ 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;
@@ -402,6 +404,8 @@ 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 3e03a91fba..848ceed4e7 100644
--- a/tools/libxc/xc_private.c
+++ b/tools/libxc/xc_private.c
@@ -771,6 +771,8 @@ 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 b7741ca543..89520488e0 100644
--- a/tools/libxc/xenctrl.h
+++ b/tools/libxc/xenctrl.h
@@ -1778,7 +1778,7 @@ 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