[PATCH] fs/hugetlbfs/inode.c: Ensure generic_hugetlb_get_unmapped_area() returns higher address than mmap_min_addr

From: Donet Tom
Date: Fri Jul 05 2024 - 03:12:39 EST


generic_hugetlb_get_unmapped_area() was returning an address less
than mmap_min_addr if the mmap argument addr, after alignment, was
less than mmap_min_addr, causing mmap to fail.

This is because current generic_hugetlb_get_unmapped_area() code does
not take into account mmap_min_addr.

This patch ensures that generic_hugetlb_get_unmapped_area() always returns
an address that is greater than mmap_min_addr.

How to reproduce
================

#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <unistd.h>

#define HUGEPAGE_SIZE (16 * 1024 * 1024)

int main() {

void *addr = mmap((void *)-1, HUGEPAGE_SIZE,
PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_ANONYMOUS | MAP_HUGETLB, -1, 0);
if (addr == MAP_FAILED) {
perror("mmap");
exit(EXIT_FAILURE);
}

snprintf((char *)addr, HUGEPAGE_SIZE, "Hello, Huge Pages!");

printf("%s\n", (char *)addr);

if (munmap(addr, HUGEPAGE_SIZE) == -1) {
perror("munmap");
exit(EXIT_FAILURE);
}

return 0;
}

Result without fix
==================
# cat /proc/meminfo |grep -i HugePages_Free
HugePages_Free: 20
# ./test
mmap: Permission denied
#

Result with fix
===============
# cat /proc/meminfo |grep -i HugePages_Free
HugePages_Free: 20
# ./test
Hello, Huge Pages!
#

Reported-by Pavithra Prakash <pavrampu@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Donet Tom <donettom@xxxxxxxxxxxxx>
---
fs/hugetlbfs/inode.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 412f295acebe..428fd2f0e4c4 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -228,7 +228,7 @@ generic_hugetlb_get_unmapped_area(struct file *file, unsigned long addr,

if (len & ~huge_page_mask(h))
return -EINVAL;
- if (len > TASK_SIZE)
+ if (len > mmap_end - mmap_min_addr)
return -ENOMEM;

if (flags & MAP_FIXED) {
@@ -240,7 +240,7 @@ generic_hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
if (addr) {
addr = ALIGN(addr, huge_page_size(h));
vma = find_vma(mm, addr);
- if (mmap_end - len >= addr &&
+ if (mmap_end - len >= addr && addr >= mmap_min_addr &&
(!vma || addr + len <= vm_start_gap(vma)))
return addr;
}
--
2.43.5