[PATCH v1] mm/mempolicy: fix migrate_to_node() assuming there is at least one VMA in a MM
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
Fixes: 39743889aaf7 ("[PATCH] Swap Migration V5: sys_migrate_pages interface") Reported-by: syzbot+3511625422f7aa637f0d@syzkaller.appspotmail.com Closes: https://lore.kernel.org/lkml/673d2696.050a0220.3c9d61.012f.GAE@google.com/T/ Cc: stable@vger.kernel.org Cc: Andrew Morton akpm@linux-foundation.org Cc: Christoph Lameter cl@linux.com Cc: Liam R. Howlett Liam.Howlett@Oracle.com Signed-off-by: David Hildenbrand david@redhat.com --- mm/mempolicy.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c index b646fab3e45e1..fbb6127e4595a 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1080,6 +1080,10 @@ static long migrate_to_node(struct mm_struct *mm, int source, int dest,
mmap_read_lock(mm); vma = find_vma(mm, 0); + if (!vma) { + mmap_read_unlock(mm); + return 0; + }
/* * This does not migrate the range, but isolates all pages that
* David Hildenbrand david@redhat.com [241120 15:12]:
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
Fixes: 39743889aaf7 ("[PATCH] Swap Migration V5: sys_migrate_pages interface") Reported-by: syzbot+3511625422f7aa637f0d@syzkaller.appspotmail.com Closes: https://lore.kernel.org/lkml/673d2696.050a0220.3c9d61.012f.GAE@google.com/T/ Cc: stable@vger.kernel.org Cc: Andrew Morton akpm@linux-foundation.org Cc: Christoph Lameter cl@linux.com Cc: Liam R. Howlett Liam.Howlett@Oracle.com Signed-off-by: David Hildenbrand david@redhat.com
I hate the extra check because syzbot can cause this as this should basically never happen in real life, but it seems we have to add it.
I wonder where else this is could show up.
Reviewed-by: Liam R. Howlett Liam.Howlett@Oracle.com
mm/mempolicy.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c index b646fab3e45e1..fbb6127e4595a 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1080,6 +1080,10 @@ static long migrate_to_node(struct mm_struct *mm, int source, int dest, mmap_read_lock(mm); vma = find_vma(mm, 0);
- if (!vma) {
mmap_read_unlock(mm);return 0;- }
/* * This does not migrate the range, but isolates all pages that -- 2.47.0
On 20.11.24 21:27, Liam R. Howlett wrote:
- David Hildenbrand david@redhat.com [241120 15:12]:
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
Fixes: 39743889aaf7 ("[PATCH] Swap Migration V5: sys_migrate_pages interface") Reported-by: syzbot+3511625422f7aa637f0d@syzkaller.appspotmail.com Closes: https://lore.kernel.org/lkml/673d2696.050a0220.3c9d61.012f.GAE@google.com/T/ Cc: stable@vger.kernel.org Cc: Andrew Morton akpm@linux-foundation.org Cc: Christoph Lameter cl@linux.com Cc: Liam R. Howlett Liam.Howlett@Oracle.com Signed-off-by: David Hildenbrand david@redhat.com
I hate the extra check because syzbot can cause this as this should basically never happen in real life, but it seems we have to add it.
I think the reproducer achieves it by doing an MADV_DONTFORK on all VMAs and then fork'ing. Likely it doesn't make sense to have a new MM without any VMAs, because it cannot do anything reasonable.
But then, I'm not 100% sure if there are other creative ways to obtain/achieve the same.
$ git grep "find_vma(mm, 0)" mm/mempolicy.c: vma = find_vma(mm, 0);
Apart from that there seems to be kernel/bpf/task_iter.c where we do curr_vma = find_vma(curr_mm, 0);
and properly check for NULL later.
So this one sticks out, and is not on anything that I consider a fast path ... easy fix. :)
Thanks!
On Wed, 20 Nov 2024 15:27:46 -0500 "Liam R. Howlett" Liam.Howlett@oracle.com wrote:
I hate the extra check because syzbot can cause this as this should basically never happen in real life, but it seems we have to add it.
So..
--- a/mm/mempolicy.c~mm-mempolicy-fix-migrate_to_node-assuming-there-is-at-least-one-vma-in-a-mm-fix +++ a/mm/mempolicy.c @@ -1080,7 +1080,7 @@ static long migrate_to_node(struct mm_st
mmap_read_lock(mm); vma = find_vma(mm, 0); - if (!vma) { + if (unlikely(!vma)) { mmap_read_unlock(mm); return 0; } _
?
On 22.11.24 07:19, Andrew Morton wrote:
On Wed, 20 Nov 2024 15:27:46 -0500 "Liam R. Howlett" Liam.Howlett@oracle.com wrote:
I hate the extra check because syzbot can cause this as this should basically never happen in real life, but it seems we have to add it.
So..
--- a/mm/mempolicy.c~mm-mempolicy-fix-migrate_to_node-assuming-there-is-at-least-one-vma-in-a-mm-fix +++ a/mm/mempolicy.c @@ -1080,7 +1080,7 @@ static long migrate_to_node(struct mm_st mmap_read_lock(mm); vma = find_vma(mm, 0);
- if (!vma) {
- if (unlikely(!vma)) { mmap_read_unlock(mm); return 0; }
_
?
Why not, at least for documentation purposes. Because I don't think this is any fast-path we really care about, so expect the runtime effects to be mostly negligible. Thanks!
* David Hildenbrand david@redhat.com [241122 04:32]:
On 22.11.24 07:19, Andrew Morton wrote:
On Wed, 20 Nov 2024 15:27:46 -0500 "Liam R. Howlett" Liam.Howlett@oracle.com wrote:
I hate the extra check because syzbot can cause this as this should basically never happen in real life, but it seems we have to add it.
So..
--- a/mm/mempolicy.c~mm-mempolicy-fix-migrate_to_node-assuming-there-is-at-least-one-vma-in-a-mm-fix +++ a/mm/mempolicy.c @@ -1080,7 +1080,7 @@ static long migrate_to_node(struct mm_st mmap_read_lock(mm); vma = find_vma(mm, 0);
- if (!vma) {
- if (unlikely(!vma)) { mmap_read_unlock(mm); return 0; }
_
?
Why not, at least for documentation purposes. Because I don't think this is any fast-path we really care about, so expect the runtime effects to be mostly negligible. Thanks!
The next email we get about this will be a bot with a micro benchmark performance drop.
Really though, I'm happy either way because of what David said.
Thanks, Liam
On 22.11.24 15:44, Liam R. Howlett wrote:
- David Hildenbrand david@redhat.com [241122 04:32]:
On 22.11.24 07:19, Andrew Morton wrote:
On Wed, 20 Nov 2024 15:27:46 -0500 "Liam R. Howlett" Liam.Howlett@oracle.com wrote:
I hate the extra check because syzbot can cause this as this should basically never happen in real life, but it seems we have to add it.
So..
--- a/mm/mempolicy.c~mm-mempolicy-fix-migrate_to_node-assuming-there-is-at-least-one-vma-in-a-mm-fix +++ a/mm/mempolicy.c @@ -1080,7 +1080,7 @@ static long migrate_to_node(struct mm_st mmap_read_lock(mm); vma = find_vma(mm, 0);
- if (!vma) {
- if (unlikely(!vma)) { mmap_read_unlock(mm); return 0; }
_
?
Why not, at least for documentation purposes. Because I don't think this is any fast-path we really care about, so expect the runtime effects to be mostly negligible. Thanks!
The next email we get about this will be a bot with a micro benchmark performance drop.
I'll be pleasantly surprised if our migration code is that fast such that this here would matter :)
linux-stable-mirror@lists.linaro.org
-
Andrew Morton -
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Liam R. Howlett