On 07.01.25 08:25, Vivek Kasireddy wrote:
There are cases when we try to pin a folio but discover that it has
not been faulted-in. So, we try to allocate it in memfd_alloc_folio()
but there is a chance that we might encounter a crash/failure
(VM_BUG_ON(!h->resv_huge_pages)) if there are no active reservations
at that instant. This issue was reported by syzbot:
kernel BUG at mm/hugetlb.c:2403!
Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5315 Comm: syz.0.0 Not tainted
6.13.0-rc5-syzkaller-00161-g63676eefb7a0 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:alloc_hugetlb_folio_reserve+0xbc/0xc0 mm/hugetlb.c:2403
Code: 1f eb 05 e8 56 18 a0 ff 48 c7 c7 40 56 61 8e e8 ba 21 cc 09 4c 89
f0 5b 41 5c 41 5e 41 5f 5d c3 cc cc cc cc e8 35 18 a0 ff 90 <0f> 0b 66
90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f
RSP: 0018:ffffc9000d3d77f8 EFLAGS: 00010087
RAX: ffffffff81ff6beb RBX: 0000000000000000 RCX: 0000000000100000
RDX: ffffc9000e51a000 RSI: 00000000000003ec RDI: 00000000000003ed
RBP: 1ffffffff34810d9 R08: ffffffff81ff6ba3 R09: 1ffffd4000093005
R10: dffffc0000000000 R11: fffff94000093006 R12: dffffc0000000000
R13: dffffc0000000000 R14: ffffea0000498000 R15: ffffffff9a4086c8
FS: 00007f77ac12e6c0(0000) GS:ffff88801fc00000(0000)
knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f77ab54b170 CR3: 0000000040b70000 CR4: 0000000000352ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
memfd_alloc_folio+0x1bd/0x370 mm/memfd.c:88
memfd_pin_folios+0xf10/0x1570 mm/gup.c:3750
udmabuf_pin_folios drivers/dma-buf/udmabuf.c:346 [inline]
udmabuf_create+0x70e/0x10c0 drivers/dma-buf/udmabuf.c:443
udmabuf_ioctl_create drivers/dma-buf/udmabuf.c:495 [inline]
udmabuf_ioctl+0x301/0x4e0 drivers/dma-buf/udmabuf.c:526
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:906 [inline]
__se_sys_ioctl+0xf5/0x170 fs/ioctl.c:892
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Therefore, to avoid this situation and fix this issue, we just need
to make a reservation before we try to allocate the folio. While at
it, also remove the VM_BUG_ON() as there is no need to crash the
system in this scenario and instead we could just fail the allocation.
Fixes: 26a8ea80929c ("mm/hugetlb: fix memfd_pin_folios resv_huge_pages leak")
Reported-by: syzbot+a504cb5bae4fe117ba94@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
Cc: Steve Sistare <steven.sistare@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 9 ++++++---
mm/memfd.c | 5 +++++
2 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index c498874a7170..e46c461210a4 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2397,12 +2397,15 @@ struct folio *alloc_hugetlb_folio_reserve(struct hstate *h, int preferred_nid,
struct folio *folio;
spin_lock_irq(&hugetlb_lock);
+ if (!h->resv_huge_pages) {
Should this be a "if (WARN_ON_ONCE(!h->resv_huge_pages)) {", because the
"_reserve" in the function indicates that this is indeed something that
must never happen?
+ spin_unlock_irq(&hugetlb_lock);
+ return NULL;
+ }
+
folio = dequeue_hugetlb_folio_nodemask(h, gfp_mask, preferred_nid,
nmask);
- if (folio) {
- VM_BUG_ON(!h->resv_huge_pages);
+ if (folio)
h->resv_huge_pages--;
- }
spin_unlock_irq(&hugetlb_lock);
return folio;
diff --git a/mm/memfd.c b/mm/memfd.c
index 35a370d75c9a..a3012c444285 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -85,6 +85,10 @@ struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
gfp_mask &= ~(__GFP_HIGHMEM | __GFP_MOVABLE);
idx >>= huge_page_order(h);
+ if (!hugetlb_reserve_pages(file_inode(memfd),
+ idx, idx + 1, NULL, 0))
+ return ERR_PTR(-ENOMEM);
+
folio = alloc_hugetlb_folio_reserve(h,
numa_node_id(),
NULL,
@@ -100,6 +104,7 @@ struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
folio_unlock(folio);
return folio;
}
+ hugetlb_unreserve_pages(file_inode(memfd), idx, idx + 1, 1);
return ERR_PTR(-ENOMEM);
Staring at hugetlb_reserve_pages() I assume this will also work as
expected if already reserved.
--
Cheers,
David / dhildenb
