confile: improve strprint()

POSIX specifies [1]: "If the value of n is zero on a call to snprintf(), nothing shall be written, the number of bytes that would have been written had n been sufficiently large excluding the terminating null shall be returned, and s may be a null pointer." But in case there are any non-sane libcs out there that do actually dereference the buffer when when 0 is passed as length to snprintf() let's give them a dummy buffer. [1]: The Open Group Base Specifications Issue 7, 2018 edition IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008) Copyright © 2001-2018 IEEE and The Open Group Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> Reported-by: Donghwa Jeong <dh48.jeong@samsung.com>

confile: improve strprint()
9496659c · Christian Brauner · 9715e65c · 9496659c
Unverified Commit 9496659c authored May 30, 2018 by Christian Brauner
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confile_utils.h src/lxc/confile_utils.h +3 -0

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--- a/src/lxc/confile_utils.h
+++ b/src/lxc/confile_utils.h
@@ -43,7 +43,10 @@
 #define strprint(str, inlen, ...)                                       \
 	do {                                                            \
+		if (str)                                                \
 			len = snprintf(str, inlen, ##__VA_ARGS__);      \
+		else                                                    \
+			len = snprintf((char *){""}, 0, ##__VA_ARGS__); \
 		if (len < 0) {                                          \
 			SYSERROR("failed to create string");            \
 			return -1;                                      \