cpuview: paththrough personality when reading cpuinfo

Let's change processing thread personality if caller personality
is different. It allows to read /proc/cpuinfo properly in
some cases (arm64 rely on current->personality inside Linux kernel).

https://github.com/lxc/lxcfs/issues/553

Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>

src/bindings.c

@@ -45,6 +45,7 @@ static bool can_use_swap;
 static bool can_use_sys_cpu;
 static bool has_versioned_opts;
 static bool memory_is_cgroupv2;
+static __u32 host_personality;
 
 static volatile sig_atomic_t reload_successful;
 
@@ -73,6 +74,11 @@ bool liblxcfs_memory_is_cgroupv2(void)
 	return memory_is_cgroupv2;
 }
 
+__u32 liblxcfs_personality(void)
+{
+	return host_personality;
+}
+
 /* Define pivot_root() if missing from the C library */
 #ifndef HAVE_PIVOT_ROOT
 static int pivot_root(const char *new_root, const char *put_old)
@@ -919,6 +925,11 @@ static void __attribute__((constructor)) lxcfs_init(void)
 		goto broken_upgrade;
 	}
 
+	if (get_task_personality(getpid(), &host_personality) < 0) {
+		lxcfs_info("Failed to retrieve host personality");
+		goto broken_upgrade;
+	}
+
 	reload_successful = 1;
 	return;
 

src/bindings.h

@@ -107,6 +107,7 @@ extern bool liblxcfs_can_use_swap(void);
 extern bool liblxcfs_memory_is_cgroupv2(void);
 extern bool liblxcfs_can_use_sys_cpu(void);
 extern bool liblxcfs_has_versioned_opts(void);
+extern __u32 liblxcfs_personality(void);
 
 static inline bool lxcfs_has_opt(struct lxcfs_opts *opts, lxcfs_opt_t opt)
 {

src/proc_fuse.c

@@ -24,6 +24,7 @@
 #include <sys/mman.h>
 #include <sys/mount.h>
 #include <sys/param.h>
+#include <sys/personality.h>
 #include <sys/socket.h>
 #include <sys/syscall.h>
 #include <sys/sysinfo.h>
@@ -1500,6 +1501,46 @@ static int proc_slabinfo_read(char *buf, size_t size, off_t offset,
 	return total_len;
 }
 
+static int proc_read_with_personality(int (*do_proc_read)(char *, size_t, off_t,
+			     struct fuse_file_info *), char *buf, size_t size, off_t offset,
+			     struct fuse_file_info *fi)
+{
+	struct fuse_context *fc = fuse_get_context();
+	__u32 host_personality = liblxcfs_personality(), caller_personality;
+	bool change_personality;
+	int ret, read_ret;
+
+	if (get_task_personality(fc->pid, &caller_personality) < 0)
+		return log_error(0, "Failed to get caller process (pid: %d) personality", fc->pid);
+
+	/* do we need to change thread personality? */
+	change_personality = host_personality != caller_personality;
+
+	if (change_personality) {
+		ret = personality(caller_personality);
+		if (ret == -1)
+			return log_error(0, "Call to personality(%d) failed: %s\n",
+				caller_personality, strerror(errno));
+
+		lxcfs_debug("task (tid: %d) personality was changed %d -> %d\n",
+				(int)syscall(SYS_gettid), ret, caller_personality);
+	}
+
+	read_ret = do_proc_read(buf, size, offset, fi);
+
+	if (change_personality) {
+		ret = personality(host_personality);
+		if (ret == -1)
+			return log_error(0, "Call to personality(%d) failed: %s\n",
+				host_personality, strerror(errno));
+
+		lxcfs_debug("task (tid: %d) personality was restored %d -> %d\n",
+				(int)syscall(SYS_gettid), ret, host_personality);
+	}
+
+	return read_ret;
+}
+
 __lxcfs_fuse_ops int proc_read(const char *path, char *buf, size_t size,
 			       off_t offset, struct fuse_file_info *fi)
 {
@@ -1514,7 +1555,7 @@ __lxcfs_fuse_ops int proc_read(const char *path, char *buf, size_t size,
 						  buf, size, offset, f);
 	case LXC_TYPE_PROC_CPUINFO:
 		if (liblxcfs_functional())
-			return proc_cpuinfo_read(buf, size, offset, fi);
+			return proc_read_with_personality(&proc_cpuinfo_read, buf, size, offset, fi);
 
 		return read_file_fuse_with_offset(LXC_TYPE_PROC_CPUINFO_PATH,
 						  buf, size, offset, f);