[v2,6.1] mm/mempolicy: fix migrate_to_node() assuming there is at least one VMA in a MM

Commit Message

Alexey Panov March 7, 2025, 12:28 p.m. UTC

From: David Hildenbrand <[e-mail]>

commit 091c1dd2d4df6edd1beebe0e5863d4034ade9572 upstream.

We currently assume that there is at least one VMA in a MM, which isn't
true.

So we might end up having find_vma() return NULL, to then de-reference
NULL.  So properly handle find_vma() returning NULL.

This fixes the report:

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 1 UID: 0 PID: 6021 Comm: syz-executor284 Not tainted 6.12.0-rc7-syzkaller-00187-gf868cd251776 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
RIP: 0010:migrate_to_node mm/mempolicy.c:1090 [inline]
RIP: 0010:do_migrate_pages+0x403/0x6f0 mm/mempolicy.c:1194
Code: ...
RSP: 0018:ffffc9000375fd08 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffffc9000375fd78 RCX: 0000000000000000
RDX: ffff88807e171300 RSI: dffffc0000000000 RDI: ffff88803390c044
RBP: ffff88807e171428 R08: 0000000000000014 R09: fffffbfff2039ef1
R10: ffffffff901cf78f R11: 0000000000000000 R12: 0000000000000003
R13: ffffc9000375fe90 R14: ffffc9000375fe98 R15: ffffc9000375fdf8
FS:  00005555919e1380(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005555919e1ca8 CR3: 000000007f12a000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 kernel_migrate_pages+0x5b2/0x750 mm/mempolicy.c:1709
 __do_sys_migrate_pages mm/mempolicy.c:1727 [inline]
 __se_sys_migrate_pages mm/mempolicy.c:1723 [inline]
 __x64_sys_migrate_pages+0x96/0x100 mm/mempolicy.c:1723
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

[[e-mail]: add unlikely()]
Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 39743889aaf7 ("[PATCH] Swap Migration V5: sys_migrate_pages interface")
Signed-off-by: David Hildenbrand <[e-mail]>
Reported-by: [e-mail]
Closes: https://lore.kernel.org/lkml/[e-mail]/T/
Reviewed-by: Liam R. Howlett <[e-mail]>
Reviewed-by: Christoph Lameter <[e-mail]>
Cc: Liam R. Howlett <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
[ Alexey: mmap_read_lock is not used in this context, so mmap_read_unlock
  is removed. Synchronization is provided by an external context in
  do_migrate_pages(). ]
Signed-off-by: Alexey Panov <[e-mail]>
---
v2: Clarify mmap_lock context in changes summary. Fix braces for a single
statement block. Rearrange the changes with a comment and VM_BUG_ON to
look more consistent with upstream.

 mm/mempolicy.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Patch

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 399d8cb48813..f60ff4727f46 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1062,13 +1062,17 @@  static int migrate_to_node(struct mm_struct *mm, int source, int dest,
 	nodes_clear(nmask);
 	node_set(source, nmask);
 
+	VM_BUG_ON(!(flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)));
+
+	vma = find_vma(mm, 0);
+	if (unlikely(!vma))
+		return 0;
+
 	/*
 	 * This does not "check" the range but isolates all pages that
 	 * need migration.  Between passing in the full user address
 	 * space range and MPOL_MF_DISCONTIG_OK, this call can not fail.
 	 */
-	vma = find_vma(mm, 0);
-	VM_BUG_ON(!(flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)));
 	queue_pages_range(mm, vma->vm_start, mm->task_size, &nmask,
 			flags | MPOL_MF_DISCONTIG_OK, &pagelist);