Map file with MAP_SHARED instead of MAP_PRIVATE

When setting up a user probe using ebpf or systemtap on a file,
fapolicyd computes a different checksum, causing (usually) denial to
occur.

eBPF is used by Microsoft's MDATP, in particular for monitoring
/usr/lib64/libpam.so.0 function calls. Through setting a user probe,
mdatp and fapolicyd cannot be used concurrently.

The reason for computing a different checksum is using mmap(MAP_PRIVATE)
which makes the hooks set by ebpf and/or systemtap be visible:
~~~
1140 char *get_hash_from_fd2(int fd, size_t size, file_hash_alg_t alg)
1141 {
 :
1165         mapped = mmap(0, size, PROT_READ, MAP_PRIVATE|MAP_POPULATE, fd, 0);
1166         if (mapped != MAP_FAILED) {
 :
~~~

A solution consists in using MAP_SHARED instead of MAP_PRIVATE.

Fixes RHEL-142628.

Author: rmetrich

src/library/file.c

@@ -1162,7 +1162,7 @@ char *get_hash_from_fd2(int fd, size_t size, file_hash_alg_t alg)
 	if (digest_length == 0)
 		return NULL;
 
-	mapped = mmap(0, size, PROT_READ, MAP_PRIVATE|MAP_POPULATE, fd, 0);
+	mapped = mmap(0, size, PROT_READ, MAP_SHARED|MAP_POPULATE, fd, 0);
 	if (mapped != MAP_FAILED) {
 		unsigned char hptr[SHA512_DIGEST_LENGTH];
 		int computed = 0;