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nsexec (CVE-2019-5736): avoid parsing environ #1982

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Merged
cyphar merged 1 commit into from
Feb 15, 2019
Merged

nsexec (CVE-2019-5736): avoid parsing environ #1982

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23 changes: 10 additions & 13 deletions libcontainer/nsenter/cloned_binary.c
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Original file line number Diff line number Diff line change
Expand Up @@ -169,31 +169,25 @@ static int parse_xargs(char *data, int data_length, char ***output)
}

/*
* "Parse" out argv and envp from /proc/self/cmdline and /proc/self/environ.
* "Parse" out argv from /proc/self/cmdline.
* This is necessary because we are running in a context where we don't have a
* main() that we can just get the arguments from.
*/
static int fetchve(char ***argv, char ***envp)
static int fetchve(char ***argv)
{
char *cmdline = NULL, *environ = NULL;
size_t cmdline_size, environ_size;
char *cmdline = NULL;
size_t cmdline_size;

cmdline = read_file("/proc/self/cmdline", &cmdline_size);
if (!cmdline)
goto error;
environ = read_file("/proc/self/environ", &environ_size);
if (!environ)
goto error;

if (parse_xargs(cmdline, cmdline_size, argv) <= 0)
goto error;
if (parse_xargs(environ, environ_size, envp) <= 0)
goto error;

return 0;

error:
free(environ);
free(cmdline);
return -EINVAL;
}
Expand Down Expand Up @@ -246,23 +240,26 @@ static int clone_binary(void)
return -EIO;
}

/* Get cheap access to the environment. */
extern char **environ;

int ensure_cloned_binary(void)
{
int execfd;
char **argv = NULL, **envp = NULL;
char **argv = NULL;

/* Check that we're not self-cloned, and if we are then bail. */
int cloned = is_self_cloned();
if (cloned > 0 || cloned == -ENOTRECOVERABLE)
return cloned;

if (fetchve(&argv, &envp) < 0)
if (fetchve(&argv) < 0)
return -EINVAL;

execfd = clone_binary();
if (execfd < 0)
return -EIO;

fexecve(execfd, argv, envp);
fexecve(execfd, argv, environ);
return -ENOEXEC;
}