From: Prasad J Pandit <p...@fedoraproject.org> Qemu guest agent while executing user commands does not seem to check length of argument list and/or environment variables passed. It may lead to integer overflow or infinite loop issues. Add check to avoid it.
Reported-by: Niu Guoxiang <niuguoxi...@huawei.com> Signed-off-by: Prasad J Pandit <p...@fedoraproject.org> --- qga/commands-posix.c | 18 ++++++++++++++++++ qga/commands-win32.c | 13 +++++++++++++ qga/commands.c | 8 ++++++-- qga/guest-agent-core.h | 2 ++ 4 files changed, 39 insertions(+), 2 deletions(-) Update v2: add helper function ga_get_arg_max() -> https://lists.gnu.org/archive/html/qemu-devel/2019-01/msg06360.html diff --git a/qga/commands-posix.c b/qga/commands-posix.c index 7ee6a33cce..e0455722e0 100644 --- a/qga/commands-posix.c +++ b/qga/commands-posix.c @@ -60,6 +60,24 @@ extern char **environ; #endif #endif +size_t ga_get_arg_max(void) +{ + /* Since kernel 2.6.23, most architectures support argument size limit + * derived from the soft RLIMIT_STACK resource limit (see getrlimit(2)). + * For these architectures, the total size is limited to 1/4 of the + * allowed stack size. (see execve(2)) + * + * struct rlimit r; + * + * getrlimit(RLIMIT_STACK, &r); + * ARG_MAX = r.rlim_cur / 4; + * + * ARG_MAX is _NOT_ the maximum number of arguments. It is size of the + * memory used to hold command line arguments and environment variables. + */ + return sysconf(_SC_ARG_MAX); +} + static void ga_wait_child(pid_t pid, int *status, Error **errp) { pid_t rpid; diff --git a/qga/commands-win32.c b/qga/commands-win32.c index 6b67f16faf..47bbddd74a 100644 --- a/qga/commands-win32.c +++ b/qga/commands-win32.c @@ -92,6 +92,19 @@ static OpenFlags guest_file_open_modes[] = { g_free(suffix); \ } while (0) +size_t ga_get_arg_max(void) +{ + /* Win32 environment has different values for the ARG_MAX constant. + * We'll go with the maximum here. + * + * https://devblogs.microsoft.com/oldnewthing/?p=41553 + * + * ARG_MAX is _NOT_ the maximum number of arguments. It is size of the + * memory used to hold command line arguments and environment variables. + */ + return 32767; +} + static OpenFlags *find_open_flag(const char *mode_str) { int mode; diff --git a/qga/commands.c b/qga/commands.c index 0c7d1385c2..425a4c405f 100644 --- a/qga/commands.c +++ b/qga/commands.c @@ -231,17 +231,21 @@ static char **guest_exec_get_args(const strList *entry, bool log) int count = 1, i = 0; /* reserve for NULL terminator */ char **args; char *str; /* for logging array of arguments */ - size_t str_size = 1; + size_t str_size = 1, arg_max; + arg_max = ga_get_arg_max(); for (it = entry; it != NULL; it = it->next) { count++; str_size += 1 + strlen(it->value); + if (str_size >= arg_max || count >= arg_max / 2) { + break; + } } str = g_malloc(str_size); *str = 0; args = g_malloc(count * sizeof(char *)); - for (it = entry; it != NULL; it = it->next) { + for (it = entry; it != NULL && i < count; it = it->next) { args[i++] = it->value; pstrcat(str, str_size, it->value); if (it->next) { diff --git a/qga/guest-agent-core.h b/qga/guest-agent-core.h index 60eae16f27..300ff7e482 100644 --- a/qga/guest-agent-core.h +++ b/qga/guest-agent-core.h @@ -46,6 +46,8 @@ const char *ga_fsfreeze_hook(GAState *s); int64_t ga_get_fd_handle(GAState *s, Error **errp); int ga_parse_whence(GuestFileWhence *whence, Error **errp); +size_t ga_get_arg_max(void); + #ifndef _WIN32 void reopen_fd_to_null(int fd); #endif -- 2.20.1