[PATCH STABLE 5.10] mm/memory: add non-anonymous page check in the copy_present_page()

[Yuanzheng Song]

The vma->anon_vma of the child process may be NULL because
the entire vma does not contain anonymous pages. In this
case, a BUG will occur when the copy_present_page() passes
a copy of a non-anonymous page of that vma to the
page_add_new_anon_rmap() to set up new anonymous rmap.

------------[ cut here ]------------
kernel BUG at mm/rmap.c:1044!
Internal error: Oops - BUG: 0 [#1] SMP
Modules linked in:
CPU: 2 PID: 3617 Comm: test Not tainted 5.10.149 #1
Hardware name: linux,dummy-virt (DT)
pstate: 80000005 (Nzcv daif -PAN -UAO -TCO BTYPE=--)
pc : __page_set_anon_rmap+0xbc/0xf8
lr : __page_set_anon_rmap+0xbc/0xf8
sp : ffff800014c1b870
x29: ffff800014c1b870 x28: 0000000000000001
x27: 0000000010100073 x26: ffff1d65c517baa8
x25: ffff1d65cab0f000 x24: ffff1d65c416d800
x23: ffff1d65cab5f248 x22: 0000000020000000
x21: 0000000000000001 x20: 0000000000000000
x19: fffffe75970023c0 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000
x15: 0000000000000000 x14: 0000000000000000
x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000000 x10: 0000000000000000
x9 : ffffc3096d5fb858 x8 : 0000000000000000
x7 : 0000000000000011 x6 : ffff5a5c9089c000
x5 : 0000000000020000 x4 : ffff5a5c9089c000
x3 : ffffc3096d200000 x2 : ffffc3096e8d0000
x1 : ffff1d65ca3da740 x0 : 0000000000000000
Call trace:
 __page_set_anon_rmap+0xbc/0xf8
 page_add_new_anon_rmap+0x1e0/0x390
 copy_pte_range+0xd00/0x1248
 copy_page_range+0x39c/0x620
 dup_mmap+0x2e0/0x5a8
 dup_mm+0x78/0x140
 copy_process+0x918/0x1a20
 kernel_clone+0xac/0x638
 __do_sys_clone+0x78/0xb0
 __arm64_sys_clone+0x30/0x40
 el0_svc_common.constprop.0+0xb0/0x308
 do_el0_svc+0x48/0xb8
 el0_svc+0x24/0x38
 el0_sync_handler+0x160/0x168
 el0_sync+0x180/0x1c0
Code: 97f8ff85 f9400294 17ffffeb 97f8ff82 (d4210000)
---[ end trace a972347688dc9bd4 ]---
Kernel panic - not syncing: Oops - BUG: Fatal exception
SMP: stopping secondary CPUs
Kernel Offset: 0x43095d200000 from 0xffff800010000000
PHYS_OFFSET: 0xffffe29a80000000
CPU features: 0x08200022,61806082
Memory Limit: none
---[ end Kernel panic - not syncing: Oops - BUG: Fatal exception ]---

This problem has been fixed by the fb3d824d1a46
("mm/rmap: split page_dup_rmap() into page_dup_file_rmap() and page_try_dup_anon_rmap()"),
but still exists in the linux-5.10.y branch.

This patch is not applicable to this version because
of the large version differences. Therefore, fix it by
adding non-anonymous page check in the copy_present_page().

Fixes: 70e806e4e645 ("mm: Do early cow for pinned pages during fork() for ptes")
Signed-off-by: Yuanzheng Song <songyuanzheng@xxxxxxxxxx>
---
 mm/memory.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index cc50fa0f4590..45973fd97be8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -823,6 +823,17 @@ copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma
 	if (likely(!page_maybe_dma_pinned(page)))
 		return 1;
 
+	/*
+	 * The vma->anon_vma of the child process may be NULL
+	 * because the entire vma does not contain anonymous pages.
+	 * A BUG will occur when the copy_present_page() passes
+	 * a copy of a non-anonymous page of that vma to the
+	 * page_add_new_anon_rmap() to set up new anonymous rmap.
+	 * Return 1 if the page is not an anonymous page.
+	*/
+	if (!PageAnon(page))
+		return 1;
+
 	new_page = *prealloc;
 	if (!new_page)
 		return -EAGAIN;
-- 
2.25.1