lib/idmapping.c: Use long constants in prctl(2), and remove 0s

The prctl(2) system-call wrapper is implemented as a variadic function.
This makes it important to pass arguments to it of the right type (and
more importantly of the right width), to avoid undefined behavior.

While at it, check errors with ==-1, not <0, which is more explicit.

Also, PR_SET_KEEPCAPS(2const) doesn't need all arguments, so it can be
called with just two of them; remove unnecessary 0s.

See-also: prctl(2), PR_SET_KEEPCAPS(2const)
Link: <https://lore.kernel.org/linux-man/ddbdyaiptesjalgfmztxideej67e3yaob7ucsmbf6qvriwxiif@dohhxrqgwhrf/T/#med306b5b003f9cc7cc2de69fcdd7ee2d056d0954>
Cc: Xi Ruoyao <xry111@xry111.site>
Cc: Lukas Slebodnik <lslebodn@fedoraproject.org>
Signed-off-by: Alejandro Colomar <alx@kernel.org>

diff --git a/lib/idmapping.c b/lib/idmapping.c
index fe3ccdfe38c08583bccbfd85dac87db25cd96fa9..5cbb6fefc0bda0962292fb775aed1d93c2945c3e 100644 (file)
--- a/lib/idmapping.c
+++ b/lib/idmapping.c
@@ -159,7 +159,7 @@ void write_mapping(int proc_dir_fd, int ranges, const struct map_range *mappings
 
        /* Align setuid- and fscaps-based new{g,u}idmap behavior. */
        if (geteuid() == 0 && geteuid() != ruid) {
-               if (prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0) < 0) {
+               if (prctl(PR_SET_KEEPCAPS, 1L) == -1) {
                        fprintf(log_get_logfd(), _("%s: Could not prctl(PR_SET_KEEPCAPS)\n"), log_get_progname());
                        exit(EXIT_FAILURE);
                }