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Re: [Qemu-devel] [PATCH] don't dereference NULL after failed strdup

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH] don't dereference NULL after failed strdup
Date: Wed, 10 Feb 2010 15:41:34 -0600
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20091209 Fedora/3.0-4.fc12 Lightning/1.0pre Thunderbird/3.0

On 02/08/2010 12:28 PM, Jim Meyering wrote:
Most of these are obvious NULL-deref bug fixes, for example,
the ones in these files:


and the first one in block/vvfat.c.
The others in block/vvfat.c may not lead to an immediate segfault, but I
traced the two schedule_rename(..., strdup(path)) uses, and a failed
strdup would appear to trigger this assertion in handle_renames_and_mkdirs:


The conversion to use qemu_strdup in envlist_to_environ is not technically
needed, but does avoid a theoretical leak in the caller when strdup fails
for one value, but later succeeds in allocating another buffer(plausible,
if one string length is much larger than the others).  The caller does
not know the length of the returned list, and as such can only free
pointers until it hits the first NULL.  If there are non-NULL pointers
beyond the first, their buffers would be leaked.  This one is admittedly

The two in linux-user/main.c are worth fixing to ensure that an
OOM error is diagnosed up front, rather than letting it provoke some
harder-to-diagnose secondary error, in case of exec failure, or worse, in
case the exec succeeds but with an invalid list of command line options.
However, considering how unlikely it is to encounter a failed strdup early
in main, this isn't a big deal.  Note that adding the required uses of
qemu_strdup here and in envlist.c induce link failures because qemu_strdup
is not currently in any library they're linked with.  So for now, I've
omitted those changes, as well as the fixes in target-i386/helper.c
and target-sparc/helper.c.

If you'd like to see the above discussion (or anything else)
in the commit log, just let me know and I'll be happy to adjust.

> From 9af42864fd1ea666bd25e2cecfdfae74c20aa8c7 Mon Sep 17 00:00:00 2001
From: Jim Meyering<address@hidden>
Date: Mon, 8 Feb 2010 18:29:29 +0100
Subject: [PATCH] don't dereference NULL after failed strdup

Handle failing strdup by replacing each use with qemu_strdup,
so as not to dereference NULL or trigger a failing assertion.
* block/curl.c (curl_open): s/\bstrdup\b/qemu_strdup/
* block/vvfat.c (init_directories): Likewise.
(get_cluster_count_for_direntry, check_directory_consistency): Likewise.
* net.c (parse_host_src_port): Likewise.

Applied, but this got ugly in git am. FYI, if you want to include comments with a patch that aren't in the git commit message, you can use a '---' separator just like with diffstat below.


Anthony Liguori

* slirp/misc.c (fork_exec): Likewise.
  block/curl.c  |    2 +-
  block/vvfat.c |   10 +++++-----
  net.c         |    2 +-
  slirp/misc.c  |    2 +-
  4 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/block/curl.c b/block/curl.c
index fe08f7b..2cf72cb 100644
--- a/block/curl.c
+++ b/block/curl.c
@@ -309,7 +309,7 @@ static int curl_open(BlockDriverState *bs, const char 
*filename, int flags)

      static int inited = 0;

-    file = strdup(filename);
+    file = qemu_strdup(filename);
      s->readahead_size = READ_AHEAD_SIZE;

      /* Parse a trailing ":readahead=#:" param, if present. */
diff --git a/block/vvfat.c b/block/vvfat.c
index d2787b9..bb707c0 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -883,7 +883,7 @@ static int init_directories(BDRVVVFATState* s,
      mapping->dir_index = 0;
      mapping->info.dir.parent_mapping_index = -1;
      mapping->first_mapping_index = -1;
-    mapping->path = strdup(dirname);
+    mapping->path = qemu_strdup(dirname);
      i = strlen(mapping->path);
      if (i>  0&&  mapping->path[i - 1] == '/')
        mapping->path[i - 1] = '\0';
@@ -1633,10 +1633,10 @@ static uint32_t 
get_cluster_count_for_direntry(BDRVVVFATState* s,

            /* rename */
            if (strcmp(basename, basename2))
-               schedule_rename(s, cluster_num, strdup(path));
+               schedule_rename(s, cluster_num, qemu_strdup(path));
        } else if (is_file(direntry))
            /* new file */
-           schedule_new_file(s, strdup(path), cluster_num);
+           schedule_new_file(s, qemu_strdup(path), cluster_num);
        else {
            return 0;
@@ -1753,10 +1753,10 @@ static int check_directory_consistency(BDRVVVFATState 
        mapping->mode&= ~MODE_DELETED;

        if (strcmp(basename, basename2))
-           schedule_rename(s, cluster_num, strdup(path));
+           schedule_rename(s, cluster_num, qemu_strdup(path));
      } else
        /* new directory */
-       schedule_mkdir(s, cluster_num, strdup(path));
+       schedule_mkdir(s, cluster_num, qemu_strdup(path));

      do {
diff --git a/net.c b/net.c
index 6ef93e6..8e951ca 100644
--- a/net.c
+++ b/net.c
@@ -96,7 +96,7 @@ int parse_host_src_port(struct sockaddr_in *haddr,
                          struct sockaddr_in *saddr,
                          const char *input_str)
-    char *str = strdup(input_str);
+    char *str = qemu_strdup(input_str);
      char *host_str = str;
      char *src_str;
      const char *src_str2;
diff --git a/slirp/misc.c b/slirp/misc.c
index 05f4fb3..dcb1dc1 100644
--- a/slirp/misc.c
+++ b/slirp/misc.c
@@ -179,7 +179,7 @@ fork_exec(struct socket *so, const char *ex, int do_pty)

                i = 0;
-               bptr = strdup(ex); /* No need to free() this */
+               bptr = qemu_strdup(ex); /* No need to free() this */
                if (do_pty == 1) {
                        /* Setup "slirp.telnetd -x" */
                        argv[i++] = "slirp.telnetd";

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