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[Qemu-devel] [PATCH v2] qga: check length of command-line & environment
From: |
P J P |
Subject: |
[Qemu-devel] [PATCH v2] qga: check length of command-line & environment variables |
Date: |
Sun, 19 May 2019 14:18:15 +0530 |
From: Prasad J Pandit <address@hidden>
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 <address@hidden>
Signed-off-by: Prasad J Pandit <address@hidden>
---
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
- [Qemu-devel] [PATCH v2] qga: check length of command-line & environment variables,
P J P <=
- Re: [Qemu-devel] [PATCH v2] qga: check length of command-line & environment variables, Daniel Henrique Barboza, 2019/05/20
- Re: [Qemu-devel] [PATCH v2] qga: check length of command-line & environment variables, Marc-André Lureau, 2019/05/22
- Re: [Qemu-devel] [PATCH v2] qga: check length of command-line & environment variables, P J P, 2019/05/23
- Re: [Qemu-devel] [PATCH v2] qga: check length of command-line & environment variables, Marc-André Lureau, 2019/05/23
- Re: [Qemu-devel] [PATCH v2] qga: check length of command-line & environment variables, P J P, 2019/05/29
- Re: [Qemu-devel] [PATCH v2] qga: check length of command-line & environment variables, Marc-André Lureau, 2019/05/29
- Re: [Qemu-devel] [PATCH v2] qga: check length of command-line & environment variables, P J P, 2019/05/29
- Re: [Qemu-devel] [PATCH v2] qga: check length of command-line & environment variables, Marc-André Lureau, 2019/05/29
- Re: [Qemu-devel] [PATCH v2] qga: check length of command-line & environment variables, P J P, 2019/05/29