From: Dmitry V. Levin <ldv@altlinux.org>
Date: Sun, 3 Jul 2016 22:15:45 +0000 (+0000)
Subject: msghdr.c: limit output when printing excessively large messages
X-Git-Tag: v4.13~72
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=bf2698a6b8fa9e78e82ec2acaeef39273e95ab17;p=strace

msghdr.c: limit output when printing excessively large messages

Limit output of struct msghdr.msg_control when
struct msghdr.msg_controllen is greater than the maximum ancillary
buffer size specified in /proc/sys/net/core/optmem_max file.

* configure.ac (AC_CHECK_FUNCS): Add open64.
* defs.h (read_int_from_file): New prototype.
* util.c (read_int_from_file): New function.
* msghdr.c (get_optmem_max): New function based on read_int_from_file.
(decode_msg_control): Use it to check control_len argument.
* tests/msg_control.c (test_big_len): New function.
(main): Use it to test printing of excessively large messages.
---

diff --git a/configure.ac b/configure.ac
index 74288d83..97b75be7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -290,6 +290,7 @@ AC_CHECK_FUNCS(m4_normalize([
 	ftruncate
 	futimens
 	if_indextoname
+	open64
 	pipe2
 	prctl
 	preadv
diff --git a/defs.h b/defs.h
index 114b98e5..bda74a34 100644
--- a/defs.h
+++ b/defs.h
@@ -511,6 +511,8 @@ int strace_vfprintf(FILE *fp, const char *fmt, va_list args);
 # define strace_vfprintf vfprintf
 #endif
 
+extern int read_int_from_file(const char *, int *);
+
 extern void set_sortby(const char *);
 extern void set_overhead(int);
 extern void qualify(const char *);
diff --git a/msghdr.c b/msghdr.c
index dd203260..3db95fa7 100644
--- a/msghdr.c
+++ b/msghdr.c
@@ -229,10 +229,33 @@ print_cmsg_type_data(struct tcb *tcp, const int cmsg_level, const int cmsg_type,
 	}
 }
 
+#ifndef UIO_MAXIOV
+# define UIO_MAXIOV 1024
+#endif
+
+static unsigned int
+get_optmem_max(void)
+{
+	static int optmem_max;
+
+	if (!optmem_max) {
+		if (read_int_from_file("/proc/sys/net/core/optmem_max",
+				       &optmem_max) || optmem_max <= 0) {
+			optmem_max = sizeof(long long) * (2 * UIO_MAXIOV + 512);
+		} else {
+			optmem_max = (optmem_max + sizeof(long long) - 1)
+				     & ~(sizeof(long long) - 1);
+		}
+	}
+
+	return optmem_max;
+}
+
 static void
-decode_msg_control(struct tcb *tcp, unsigned long addr, const size_t control_len)
+decode_msg_control(struct tcb *tcp, unsigned long addr,
+		   const size_t in_control_len)
 {
-	if (!control_len)
+	if (!in_control_len)
 		return;
 	tprints(", msg_control=");
 
@@ -242,6 +265,9 @@ decode_msg_control(struct tcb *tcp, unsigned long addr, const size_t control_len
 #endif
 			sizeof(struct cmsghdr);
 
+	size_t control_len =
+		in_control_len > get_optmem_max()
+		? get_optmem_max() : in_control_len;
 	size_t buf_len = control_len;
 	char *buf = buf_len < cmsg_size ? NULL : malloc(buf_len);
 	if (!buf || umoven(tcp, addr, buf_len, buf) < 0) {
@@ -299,6 +325,8 @@ decode_msg_control(struct tcb *tcp, unsigned long addr, const size_t control_len
 	if (buf_len) {
 		tprints(", ");
 		printaddr(addr + (control_len - buf_len));
+	} else if (control_len < in_control_len) {
+		tprints(", ...");
 	}
 	tprints("]");
 	free(buf);
diff --git a/tests/msg_control.c b/tests/msg_control.c
index 8d288834..d5ed278d 100644
--- a/tests/msg_control.c
+++ b/tests/msg_control.c
@@ -49,6 +49,10 @@
 # define SCM_SECURITY 3
 #endif
 
+#ifndef UIO_MAXIOV
+# define UIO_MAXIOV 1024
+#endif
+
 #define MIN_SIZE_OF(type, member) \
 	(offsetof(type, member) + sizeof(((type *) 0)->member))
 
@@ -652,6 +656,39 @@ test_unknown_level(struct msghdr *const mh, void *const page)
 	       (unsigned) mh->msg_controllen, rc, errno2name());
 }
 
+static void
+test_big_len(struct msghdr *const mh)
+{
+	int optmem_max;
+
+	if (read_int_from_file("/proc/sys/net/core/optmem_max", &optmem_max)
+	    || optmem_max <= 0 || optmem_max > 0x100000)
+		optmem_max = sizeof(long long) * (2 * UIO_MAXIOV + 512);
+	optmem_max = (optmem_max + sizeof(long long) - 1)
+		     & ~(sizeof(long long) - 1);
+
+	const size_t len = optmem_max * 2;
+	struct cmsghdr *const cmsg = tail_alloc(len);
+	cmsg->cmsg_len = len;
+	cmsg->cmsg_level = SOL_SOCKET;
+	cmsg->cmsg_type = SCM_RIGHTS;
+
+	mh->msg_control = cmsg;
+	mh->msg_controllen = len;
+
+	int rc = sendmsg(-1, mh, 0);
+	if (EBADF != errno)
+		perror_msg_and_skip("sendmsg");
+
+	printf("sendmsg(-1, {msg_name=NULL, msg_namelen=0, msg_iov=NULL"
+	       ", msg_iovlen=0, msg_control=[{cmsg_len=%u"
+	       ", cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS",
+	       (unsigned) cmsg->cmsg_len);
+	print_fds(cmsg, optmem_max);
+	printf("}, ...], msg_controllen=%lu, msg_flags=0}, 0) = %d %s (%m)\n",
+	       (unsigned long) len, rc, errno2name());
+}
+
 int main(int ac, const char **av)
 {
 	int rc = sendmsg(-1, 0, 0);
@@ -659,6 +696,7 @@ int main(int ac, const char **av)
 
 	struct msghdr *mh = tail_alloc(sizeof(*mh));
 	memset(mh, 0, sizeof(*mh));
+	test_big_len(mh);
 
 	rc = sendmsg(-1, mh + 1, 0);
 	printf("sendmsg(-1, %p, 0) = %d %s (%m)\n",
diff --git a/util.c b/util.c
index 31227554..c99136d2 100644
--- a/util.c
+++ b/util.c
@@ -1436,3 +1436,45 @@ printargs_d(struct tcb *tcp)
 			(int) tcp->u_arg[i]);
 	return RVAL_DECODED;
 }
+
+#if defined _LARGEFILE64_SOURCE && defined HAVE_OPEN64
+# define open_file open64
+#else
+# define open_file open
+#endif
+
+int
+read_int_from_file(const char *const fname, int *const pvalue)
+{
+	const int fd = open_file(fname, O_RDONLY);
+	if (fd < 0)
+		return -1;
+
+	long lval;
+	char buf[sizeof(lval) * 3];
+	int n = read(fd, buf, sizeof(buf) - 1);
+	int saved_errno = errno;
+	close(fd);
+
+	if (n < 0) {
+		errno = saved_errno;
+		return -1;
+	}
+
+	buf[n] = '\0';
+	char *endptr = 0;
+	errno = 0;
+	lval = strtol(buf, &endptr, 10);
+	if (!endptr || (*endptr && '\n' != *endptr)
+#if INT_MAX < LONG_MAX
+	    || lval > INT_MAX || lval < INT_MIN
+#endif
+	    || ERANGE == errno) {
+		if (!errno)
+			errno = EINVAL;
+		return -1;
+	}
+
+	*pvalue = (int) lval;
+	return 0;
+}