Re: [PATCH] nilfs2: fix NULL pointer dereference in nilfs_palloc_commit_free_entry()
From: Ryusuke Konishi
Date: Mon Nov 14 2022 - 13:39:56 EST
On Mon, Nov 14, 2022 at 12:39 PM Peng Zhang wrote:
>
> From: ZhangPeng <zhangpeng362@xxxxxxxxxx>
>
> Syzbot reported a null-ptr-deref bug:
>
> NILFS (loop0): segctord starting. Construction interval = 5 seconds, CP
> frequency < 30 seconds
> general protection fault, probably for non-canonical address
> 0xdffffc0000000002: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
> CPU: 1 PID: 3603 Comm: segctord Not tainted
> 6.1.0-rc2-syzkaller-00105-gb229b6ca5abb #0
> Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google
> 10/11/2022
> RIP: 0010:nilfs_palloc_commit_free_entry+0xe5/0x6b0
> fs/nilfs2/alloc.c:608
> Code: 00 00 00 00 fc ff df 80 3c 02 00 0f 85 cd 05 00 00 48 b8 00 00 00
> 00 00 fc ff df 4c 8b 73 08 49 8d 7e 10 48 89 fa 48 c1 ea 03 <80> 3c 02
> 00 0f 85 26 05 00 00 49 8b 46 10 be a6 00 00 00 48 c7 c7
> RSP: 0018:ffffc90003dff830 EFLAGS: 00010212
> RAX: dffffc0000000000 RBX: ffff88802594e218 RCX: 000000000000000d
> RDX: 0000000000000002 RSI: 0000000000002000 RDI: 0000000000000010
> RBP: ffff888071880222 R08: 0000000000000005 R09: 000000000000003f
> R10: 000000000000000d R11: 0000000000000000 R12: ffff888071880158
> R13: ffff88802594e220 R14: 0000000000000000 R15: 0000000000000004
> FS: 0000000000000000(0000) GS:ffff8880b9b00000(0000)
> knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fb1c08316a8 CR3: 0000000018560000 CR4: 0000000000350ee0
> Call Trace:
> <TASK>
> nilfs_dat_commit_free fs/nilfs2/dat.c:114 [inline]
> nilfs_dat_commit_end+0x464/0x5f0 fs/nilfs2/dat.c:193
> nilfs_dat_commit_update+0x26/0x40 fs/nilfs2/dat.c:236
> nilfs_btree_commit_update_v+0x87/0x4a0 fs/nilfs2/btree.c:1940
> nilfs_btree_commit_propagate_v fs/nilfs2/btree.c:2016 [inline]
> nilfs_btree_propagate_v fs/nilfs2/btree.c:2046 [inline]
> nilfs_btree_propagate+0xa00/0xd60 fs/nilfs2/btree.c:2088
> nilfs_bmap_propagate+0x73/0x170 fs/nilfs2/bmap.c:337
> nilfs_collect_file_data+0x45/0xd0 fs/nilfs2/segment.c:568
> nilfs_segctor_apply_buffers+0x14a/0x470 fs/nilfs2/segment.c:1018
> nilfs_segctor_scan_file+0x3f4/0x6f0 fs/nilfs2/segment.c:1067
> nilfs_segctor_collect_blocks fs/nilfs2/segment.c:1197 [inline]
> nilfs_segctor_collect fs/nilfs2/segment.c:1503 [inline]
> nilfs_segctor_do_construct+0x12fc/0x6af0 fs/nilfs2/segment.c:2045
> nilfs_segctor_construct+0x8e3/0xb30 fs/nilfs2/segment.c:2379
> nilfs_segctor_thread_construct fs/nilfs2/segment.c:2487 [inline]
> nilfs_segctor_thread+0x3c3/0xf30 fs/nilfs2/segment.c:2570
> kthread+0x2e4/0x3a0 kernel/kthread.c:376
> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
> </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:nilfs_palloc_commit_free_entry+0xe5/0x6b0
> fs/nilfs2/alloc.c:608
> Code: 00 00 00 00 fc ff df 80 3c 02 00 0f 85 cd 05 00 00 48 b8 00 00 00
> 00 00 fc ff df 4c 8b 73 08 49 8d 7e 10 48 89 fa 48 c1 ea 03 <80> 3c 02
> 00 0f 85 26 05 00 00 49 8b 46 10 be a6 00 00 00 48 c7 c7
> RSP: 0018:ffffc90003dff830 EFLAGS: 00010212
> RAX: dffffc0000000000 RBX: ffff88802594e218 RCX: 000000000000000d
> RDX: 0000000000000002 RSI: 0000000000002000 RDI: 0000000000000010
> RBP: ffff888071880222 R08: 0000000000000005 R09: 000000000000003f
> R10: 000000000000000d R11: 0000000000000000 R12: ffff888071880158
> R13: ffff88802594e220 R14: 0000000000000000 R15: 0000000000000004
> FS: 0000000000000000(0000) GS:ffff8880b9b00000(0000)
> knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fb1c08316a8 CR3: 0000000018560000 CR4: 0000000000350ee0
> ----------------
> Code disassembly (best guess), 7 bytes skipped:
> 0: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1)
> 4: 0f 85 cd 05 00 00 jne 0x5d7
> a: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
> 11: fc ff df
> 14: 4c 8b 73 08 mov 0x8(%rbx),%r14
> 18: 49 8d 7e 10 lea 0x10(%r14),%rdi
> 1c: 48 89 fa mov %rdi,%rdx
> 1f: 48 c1 ea 03 shr $0x3,%rdx
> * 23: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1) <-- trapping
> instruction
> 27: 0f 85 26 05 00 00 jne 0x553
> 2d: 49 8b 46 10 mov 0x10(%r14),%rax
> 31: be a6 00 00 00 mov $0xa6,%esi
> 36: 48 rex.W
> 37: c7 .byte 0xc7
> 38: c7 .byte 0xc7
>
> When maxlevelp is 1, there is a case where req->pr_desc_bh is NULL and
> blocknr is 0, because nilfs_dat_commit_alloc() will modify the blocknr
> of oldreq at one level higher to 0. And we don't have a NULL check on
> req->pr_desc_bh and req->pr_bitmap_bh in
> nilfs_palloc_commit_free_entry() function, so when req->pr_desc_bh is
> NULL and kmap() dereferences a NULL pointer, it leads to above crash.
> Fix this by adding a NULL check on req->pr_desc_bh and req->pr_bitmap_bh
> before nilfs_palloc_commit_free_entry() in nilfs_dat_commit_free().
>
> Reported-by: syzbot+ebe05ee8e98f755f61d0@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: bd8169efae8b ("nilfs2: add update functions of virtual block address to dat")
> Signed-off-by: ZhangPeng <zhangpeng362@xxxxxxxxxx>
> ---
> fs/nilfs2/dat.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/fs/nilfs2/dat.c b/fs/nilfs2/dat.c
> index 3b55e239705f..84ce050a8fa3 100644
> --- a/fs/nilfs2/dat.c
> +++ b/fs/nilfs2/dat.c
> @@ -111,6 +111,9 @@ static void nilfs_dat_commit_free(struct inode *dat,
> kunmap_atomic(kaddr);
>
> nilfs_dat_commit_entry(dat, req);
> +
> + if (req->pr_desc_bh == NULL || req->pr_bitmap_bh == NULL)
> + return;
> nilfs_palloc_commit_free_entry(dat, req);
> }
>
> --
> 2.25.1
>
Thank you for your help.
This patch actually fixes the NULL pointer dereference, and doesn't
seem to cause any regressions so far.
But, if de_blocknr is 0 in the first place, it assumes that
req->pr_desc_bh and req->pr_bitmap_bh are set properly in the
corresponding "prepare" operation, nilfs_dat_prepare_end(), so I'd
like to review in a little more detail why that is broken.
Thanks,
Ryusuke Konishi