Re: [f2fs-dev] [PATCH -next] f2fs: fix use after free in f2fs_fill_super

[Chao Yu <chao@kernel.org>]

On 2021/7/22 12:41, Jack Qiu wrote:
> The root cause is shrink_dcache_sb after sbi has been freed.
> So call shrink_dcache_sb before free sbi and other resources.
> 
> ==================================================================
> BUG: KASAN: use-after-free in f2fs_evict_inode+0x31c/0xde5
> Read of size 4 at addr ffff8881d97f0d50 by task syz-executor.3/8729
> 
> PU: 1 PID: 8729 Comm: syz-executor.3 Not tainted
> 4.19.195-00002-g67dceea04431-dirty #31

Does this bug below to 4.19.195?

> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31
> 04/01/2014
> Call Trace:
>   dump_stack+0xe5/0x14b
>   ? f2fs_evict_inode+0x31c/0xde5
>   print_address_description+0x6c/0x237
>   ? f2fs_evict_inode+0x31c/0xde5
>   kasan_report.cold+0x88/0x2a3
>   f2fs_evict_inode+0x31c/0xde5
>   ? full_proxy_open.cold+0x12/0x12
>   evict+0x2cd/0x5f0
>   iput+0x3d9/0x6f0
>   dentry_unlink_inode+0x273/0x330
>   __dentry_kill+0x340/0x5e0
>   dentry_kill+0xb7/0x740
>   shrink_dentry_list+0x256/0x660
>   shrink_dcache_sb+0x11f/0x1d0
>   ? shrink_dentry_list+0x660/0x660
>   ? __kasan_slab_free+0x144/0x180
>   f2fs_fill_super+0x2a34/0x4a80
>   ? f2fs_sanity_check_ckpt.cold+0x2b6/0x2b6
>   ? wait_for_completion+0x3c0/0x3c0
>   ? set_blocksize+0x230/0x2b0
>   mount_bdev+0x2c1/0x370
>   ? f2fs_sanity_check_ckpt.cold+0x2b6/0x2b6
>   mount_fs+0x4c/0x1c0
>   vfs_kern_mount.part.0+0x60/0x3d0
>   do_mount+0x367/0x2570
>   ? kasan_unpoison_shadow+0x33/0x40
>   ? copy_mount_string+0x40/0x40
>   ? kmem_cache_alloc_trace+0x13f/0x2b0
>   ? _copy_from_user+0x94/0x100
>   ? copy_mount_options+0x1f1/0x2e0
>   ksys_mount+0xa0/0x100
>   __x64_sys_mount+0xbf/0x160
>   do_syscall_64+0xc2/0x190
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x47938e
> Code: 48 c7 c1 b4 ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84
> 00 00 00 00 00 90 f3 0f 1e fa 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01
> f0 ff ff 73 01 c3 48 c7 c1 b4 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fed673b6a48 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 0000000020000200 RCX: 000000000047938e
> RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007fed673b6aa0
> RBP: 00007fed673b6ae0 R08: 00007fed673b6ae0 R09: 0000000020000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000020000000
> R13: 0000000020000100 R14: 00007fed673b6aa0 R15: 0000000020000b00
> 
> Allocated by task 8729:
>   kasan_kmalloc+0xc2/0xe0
>   kmem_cache_alloc_trace+0x13f/0x2b0
>   f2fs_fill_super+0x124/0x4a80
>   mount_bdev+0x2c1/0x370
>   mount_fs+0x4c/0x1c0
>   vfs_kern_mount.part.0+0x60/0x3d0
>   do_mount+0x367/0x2570
>   ksys_mount+0xa0/0x100
>   __x64_sys_mount+0xbf/0x160
>   do_syscall_64+0xc2/0x190
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Freed by task 8729:
>   __kasan_slab_free+0x12f/0x180
>   kfree+0xfa/0x2a0
>   f2fs_fill_super+0x2a00/0x4a80
>   mount_bdev+0x2c1/0x370
>   mount_fs+0x4c/0x1c0
>   vfs_kern_mount.part.0+0x60/0x3d0
>   do_mount+0x367/0x2570
>   ksys_mount+0xa0/0x100
>   __x64_sys_mount+0xbf/0x160
>   do_syscall_64+0xc2/0x190
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Signed-off-by: Jack Qiu <jack.qiu@huawei.com>
> ---
>   fs/f2fs/super.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 8fecd3050ccd..b041625e06ce 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -4229,6 +4229,8 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
>   free_compress_inode:
>   	f2fs_destroy_compress_inode(sbi);
>   free_root_inode:
> +	if (retry_cnt > 0 && skip_recovery)
> +		shrink_dcache_sb(sb);

Compare to 4.19, last f2fs adds evict_inodes() before f2fs_unregister_sysfs(),
could you please check whether this can fix the issue?

Thanks,

>   	dput(sb->s_root);
>   	sb->s_root = NULL;
>   free_node_inode:
> @@ -4285,7 +4287,6 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
>   	/* give only one another chance */
>   	if (retry_cnt > 0 && skip_recovery) {
>   		retry_cnt--;
> -		shrink_dcache_sb(sb);
>   		goto try_onemore;
>   	}
>   	return err;
> --
> 2.17.1
> 


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