um: Don't use vfprintf() for os_info()

[ Upstream commit 236f9fe39b02c15fa5530b53e9cca48354394389 ]

The threads allocated inside the kernel have only a single page of
stack. Unfortunately, the vfprintf function in standard glibc may use
too much stack-space, overflowing it.

To make os_info safe to be used by helper threads, use the kernel
vscnprintf function into a smallish buffer and write out the information
to stderr.

Signed-off-by: Benjamin Berg <benjamin@sipsolutions.net>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/um/os-Linux/util.c b/arch/um/os-Linux/util.c
index fc0f2a9..1dca4ff 100644 (file)
--- a/arch/um/os-Linux/util.c
+++ b/arch/um/os-Linux/util.c
@@ -173,23 +173,38 @@ __uml_setup("quiet", quiet_cmd_param,
 "quiet\n"
 "    Turns off information messages during boot.\n\n");
 
+/*
+ * The os_info/os_warn functions will be called by helper threads. These
+ * have a very limited stack size and using the libc formatting functions
+ * may overflow the stack.
+ * So pull in the kernel vscnprintf and use that instead with a fixed
+ * on-stack buffer.
+ */
+int vscnprintf(char *buf, size_t size, const char *fmt, va_list args);
+
 void os_info(const char *fmt, ...)
 {
+       char buf[256];
        va_list list;
+       int len;
 
        if (quiet_info)
                return;
 
        va_start(list, fmt);
-       vfprintf(stderr, fmt, list);
+       len = vscnprintf(buf, sizeof(buf), fmt, list);
+       fwrite(buf, len, 1, stderr);
        va_end(list);
 }
 
 void os_warn(const char *fmt, ...)
 {
+       char buf[256];
        va_list list;
+       int len;
 
        va_start(list, fmt);
-       vfprintf(stderr, fmt, list);
+       len = vscnprintf(buf, sizeof(buf), fmt, list);
+       fwrite(buf, len, 1, stderr);
        va_end(list);
 }