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[Qemu-devel] [PATCH] linux-user: hijack open() for thread directories
From: |
Shu-Chun Weng |
Subject: |
[Qemu-devel] [PATCH] linux-user: hijack open() for thread directories |
Date: |
Wed, 21 Aug 2019 13:19:21 -0700 |
Besides /proc/self|<pid>, files under /proc/thread-self and
/proc/self|<pid>/task/<tid> also expose host information to the guest
program. This patch adds them to the hijack infrastracture. Note that
is_proc_myself() does not check if the <tid> matches the current thread
and is thus only suitable for procfs files that are identical for all
threads in the same process.
Behavior verified with guest program:
long main_thread_tid;
long gettid() {
return syscall(SYS_gettid);
}
void print_info(const char* cxt, const char* dir) {
char buf[1024];
FILE* fp;
snprintf(buf, sizeof(buf), "%s/cmdline", dir);
fp = fopen(buf, "r");
if (fp == NULL) {
printf("%s: can't open %s\n", cxt, buf);
} else {
fgets(buf, sizeof(buf), fp);
printf("%s %s cmd: %s\n", cxt, dir, buf);
fclose(fp);
}
snprintf(buf, sizeof(buf), "%s/maps", dir);
fp = fopen(buf, "r");
if (fp == NULL) {
printf("%s: can't open %s\n", cxt, buf);
} else {
char seen[128][128];
int n = 0, is_new = 0;
while(fgets(buf, sizeof(buf), fp) != NULL) {
const char* p = strrchr(buf, ' ');
if (p == NULL || *(p + 1) == '\n') {
continue;
}
++p;
is_new = 1;
for (int i = 0; i < n; ++i) {
if (strncmp(p, seen[i], sizeof(seen[i])) == 0) {
is_new = 0;
break;
}
}
if (is_new) {
printf("%s %s map: %s", cxt, dir, p);
if (n < 128) {
strncpy(seen[n], p, sizeof(seen[n]));
seen[n][sizeof(seen[n]) - 1] = '\0';
++n;
}
}
}
fclose(fp);
}
}
void* thread_main(void* _) {
char buf[1024];
print_info("Child", "/proc/thread-self");
snprintf(buf, sizeof(buf), "/proc/%ld/task/%ld", (long) getpid(),
main_thread_tid);
print_info("Child", buf);
snprintf(buf, sizeof(buf), "/proc/%ld/task/%ld", (long) getpid(), (long)
gettid());
print_info("Child", buf);
return NULL;
}
int main() {
char buf[1024];
pthread_t thread;
int ret;
print_info("Main", "/proc/thread-self");
print_info("Main", "/proc/self");
snprintf(buf, sizeof(buf), "/proc/%ld", (long) getpid());
print_info("Main", buf);
main_thread_tid = gettid();
snprintf(buf, sizeof(buf), "/proc/self/task/%ld", main_thread_tid);
print_info("Main", buf);
snprintf(buf, sizeof(buf), "/proc/%ld/task/%ld", (long) getpid(),
main_thread_tid);
print_info("Main", buf);
if ((ret = pthread_create(&thread, NULL, &thread_main, NULL)) < 0) {
printf("ptherad_create failed: %s (%d)\n", strerror(ret), ret);
}
pthread_join(thread, NULL);
return 0;
}
Signed-off-by: Shu-Chun Weng <address@hidden>
---
linux-user/syscall.c | 40 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 40 insertions(+)
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 8367cb138d..73fe82bcc7 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -6968,17 +6968,57 @@ static int open_self_auxv(void *cpu_env, int fd)
return 0;
}
+static int consume_task_directories(const char **filename)
+{
+ if (!strncmp(*filename, "task/", strlen("task/"))) {
+ *filename += strlen("task/");
+ if (**filename < '1' || **filename > '9') {
+ return 0;
+ }
+ /*
+ * Don't care about the exact tid.
+ * XXX: this allows opening files under /proc/self|<pid>/task/<n> where
+ * <n> is not a valid thread id. Consider checking if the file
+ * actually exists.
+ */
+ const char *p = *filename + 1;
+ while (*p >= '0' && *p <= '9') {
+ ++p;
+ }
+ if (*p == '/') {
+ *filename = p + 1;
+ return 1;
+ } else {
+ return 0;
+ }
+ }
+ return 1;
+}
+
+/*
+ * Determines if filename refer to a procfs file for the current process or any
+ * thread within the current process. This function should only be used to
check
+ * for files that have identical contents in all threads, e.g. exec, maps, etc.
+ */
static int is_proc_myself(const char *filename, const char *entry)
{
if (!strncmp(filename, "/proc/", strlen("/proc/"))) {
filename += strlen("/proc/");
if (!strncmp(filename, "self/", strlen("self/"))) {
filename += strlen("self/");
+ if (!consume_task_directories(&filename)) {
+ return 0;
+ }
+ } else if (!strncmp(filename, "thread-self/", strlen("thread-self/")))
{
+ filename += strlen("thread-self/");
} else if (*filename >= '1' && *filename <= '9') {
char myself[80];
snprintf(myself, sizeof(myself), "%d/", getpid());
if (!strncmp(filename, myself, strlen(myself))) {
filename += strlen(myself);
+ if (!consume_task_directories(&filename)) {
+ return 0;
+ }
} else {
return 0;
}
--
2.23.0.rc1.153.gdeed80330f-goog
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Shu-Chun Weng <=