coredump: fix core_pattern input validation

In be1e0283021e ("coredump: don't pointlessly check and spew warnings")
we tried to fix input validation so it only happens during a write to
core_pattern. This would avoid needlessly logging a lot of warnings
during a read operation. However the logic accidently got inverted in
this commit. Fix it so the input validation only happens on write and is
skipped on read.

Fixes: be1e0283021e ("coredump: don't pointlessly check and spew warnings")
Fixes: 16195d2c7dd2 ("coredump: validate socket name as it is written")
Reviewed-by: Jan Kara <[e-mail]>
Reported-by: Yu Watanabe <[e-mail]>
Signed-off-by: Christian Brauner <[e-mail]>

fs/coredump.c

···
 	ssize_t retval;
 	char old_core_pattern[CORENAME_MAX_SIZE];
 
-	if (write)
+	if (!write)
 		return proc_dostring(table, write, buffer, lenp, ppos);
 
 	retval = strscpy(old_core_pattern, core_pattern, CORENAME_MAX_SIZE);

fs/exec.c

···
 {
 	int error = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 
-	if (!error && !write)
+	if (!error && write)
 		validate_coredump_safety();
 	return error;
 }