Re: [PATCH next] fs/9p: fix uaf in in v9fs_stat2inode_dotl

Jakub Kicinski
2024-03-22T01:28:26Z

On Mon, 4 Mar 2024 22:02:29 +0900 asmadeus@codewreck.org wrote:
> Lizhi Xu wrote on Fri, Feb 02, 2024 at 08:15:31PM +0800:
> > The incorrect logical order of accessing the st object code in v9fs_fid_iget_dotl
> > is causing this uaf.
>
> Thanks for the fix!
>
> Eric, this is also for your tree.
>
> > Fixes: 724a08450f74 ("fs/9p: simplify iget to remove unnecessary paths")
>
> (careful if you rebase your tree as this commit isn't merged yet)
>
> > Reported-and-tested-by: syzbot+7a3d75905ea1a830dbe5@syzkaller.appspotmail.com
> > Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
>
> Reviewed-by: Dominique Martinet <asmadeus@codewreck.org>

Looks like this UAF is in Linus's tree now, and possibly getting hit
by anyone using virtme to test the kernel? I can't vouch for the
correctness of the fix but it does make the KASAN splat go away for me.

[ 12.474676][ T1] ==================================================================
[ 12.474870][ T1] BUG: KASAN: slab-use-after-free in v9fs_stat2inode_dotl+0x9d6/0xb80
[ 12.475060][ T1] Read of size 8 at addr ffff888002bdbad8 by task swapper/0/1
[ 12.475248][ T1]
[ 12.475314][ T1] CPU: 3 PID: 1 Comm: swapper/0 Not tainted 6.8.0-virtme #1
[ 12.475503][ T1] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 12.475811][ T1] Call Trace:
[ 12.475908][ T1] <TASK>
[ 12.475976][ T1] dump_stack_lvl+0x82/0xd0
[ 12.476133][ T1] print_address_description.constprop.0+0x2c/0x3b0
[ 12.476295][ T1] ? v9fs_stat2inode_dotl+0x9d6/0xb80
[ 12.476425][ T1] print_report+0xb4/0x270
[ 12.476552][ T1] ? kasan_addr_to_slab+0x4e/0x90
[ 12.476679][ T1] kasan_report+0xbd/0xf0
[ 12.476775][ T1] ? v9fs_stat2inode_dotl+0x9d6/0xb80
[ 12.476903][ T1] v9fs_stat2inode_dotl+0x9d6/0xb80
[ 12.477053][ T1] v9fs_fid_iget_dotl+0x18c/0x210
[ 12.477180][ T1] v9fs_mount+0x3fe/0x7d0
[ 12.477281][ T1] ? __pfx_v9fs_mount+0x10/0x10
[ 12.477406][ T1] ? vfs_parse_fs_string+0xdb/0x130
[ 12.477533][ T1] ? __pfx_vfs_parse_fs_string+0x10/0x10
[ 12.477660][ T1] ? __pfx_v9fs_mount+0x10/0x10
[ 12.477786][ T1] legacy_get_tree+0x107/0x200
[ 12.477912][ T1] vfs_get_tree+0x8a/0x2e0
[ 12.478042][ T1] do_new_mount+0x27d/0x5e0
[ 12.478170][ T1] ? __pfx_do_new_mount+0x10/0x10
[ 12.478294][ T1] ? __pfx___debug_check_no_obj_freed+0x10/0x10
[ 12.478453][ T1] ? __virt_addr_valid+0x227/0x420
[ 12.478583][ T1] path_mount+0x271/0x14f0
[ 12.478713][ T1] ? __pfx_path_mount+0x10/0x10
[ 12.478840][ T1] ? kmem_cache_free+0xd7/0x220
[ 12.478970][ T1] ? kern_path+0x3d/0x50
[ 12.479068][ T1] init_mount+0x9d/0xf0
[ 12.479164][ T1] ? __pfx_init_mount+0x10/0x10
[ 12.479292][ T1] do_mount_root+0xbc/0x330
[ 12.479419][ T1] mount_root_generic+0x22c/0x470
[ 12.479550][ T1] ? __pfx_mount_root_generic+0x10/0x10
[ 12.479680][ T1] ? mount_root+0x25b/0x2f0
[ 12.479807][ T1] prepare_namespace+0xa5/0x2d0
[ 12.479933][ T1] ? __pfx_prepare_namespace+0x10/0x10
[ 12.480061][ T1] ? __pfx_kernel_init+0x10/0x10
[ 12.480188][ T1] kernel_init+0x20/0x200
[ 12.480285][ T1] ? __pfx_kernel_init+0x10/0x10
[ 12.480410][ T1] ret_from_fork+0x31/0x70
[ 12.480543][ T1] ? __pfx_kernel_init+0x10/0x10
[ 12.480670][ T1] ret_from_fork_asm+0x1a/0x30
[ 12.480807][ T1] </TASK>
[ 12.480904][ T1]
[ 12.480969][ T1] Allocated by task 1:
[ 12.481063][ T1] kasan_save_stack+0x24/0x50
[ 12.481191][ T1] kasan_save_track+0x14/0x30
[ 12.481323][ T1] __kasan_kmalloc+0x7f/0x90
[ 12.481449][ T1] p9_client_getattr_dotl+0x4c/0x1a0
[ 12.481576][ T1] v9fs_fid_iget_dotl+0xca/0x210
[ 12.481706][ T1] v9fs_mount+0x3fe/0x7d0
[ 12.481801][ T1] legacy_get_tree+0x107/0x200
[ 12.481927][ T1] vfs_get_tree+0x8a/0x2e0
[ 12.482053][ T1] do_new_mount+0x27d/0x5e0
[ 12.482178][ T1] path_mount+0x271/0x14f0
[ 12.482303][ T1] init_mount+0x9d/0xf0
[ 12.482397][ T1] do_mount_root+0xbc/0x330
[ 12.482523][ T1] mount_root_generic+0x22c/0x470
[ 12.482649][ T1] prepare_namespace+0xa5/0x2d0
[ 12.482779][ T1] kernel_init+0x20/0x200
[ 12.482876][ T1] ret_from_fork+0x31/0x70
[ 12.483002][ T1] ret_from_fork_asm+0x1a/0x30
[ 12.483128][ T1]
[ 12.483191][ T1] Freed by task 1:
[ 12.483283][ T1] kasan_save_stack+0x24/0x50
[ 12.483409][ T1] kasan_save_track+0x14/0x30
[ 12.483535][ T1] kasan_save_free_info+0x3b/0x60
[ 12.483662][ T1] __kasan_slab_free+0xf4/0x180
[ 12.483788][ T1] kfree+0xd3/0x230
[ 12.483886][ T1] v9fs_fid_iget_dotl+0x15e/0x210
[ 12.484017][ T1] v9fs_mount+0x3fe/0x7d0
[ 12.484112][ T1] legacy_get_tree+0x107/0x200
[ 12.484238][ T1] vfs_get_tree+0x8a/0x2e0
[ 12.484365][ T1] do_new_mount+0x27d/0x5e0
[ 12.484492][ T1] path_mount+0x271/0x14f0
[ 12.484619][ T1] init_mount+0x9d/0xf0
[ 12.484713][ T1] do_mount_root+0xbc/0x330
[ 12.484846][ T1] mount_root_generic+0x22c/0x470
[ 12.484974][ T1] prepare_namespace+0xa5/0x2d0
[ 12.485100][ T1] kernel_init+0x20/0x200
[ 12.485196][ T1] ret_from_fork+0x31/0x70
[ 12.485324][ T1] ret_from_fork_asm+0x1a/0x30
[ 12.485449][ T1]
[ 12.485512][ T1] The buggy address belongs to the object at ffff888002bdbad8
[ 12.485512][ T1] which belongs to the cache kmalloc-192 of size 192
[ 12.485825][ T1] The buggy address is located 0 bytes inside of
[ 12.485825][ T1] freed 192-byte region [ffff888002bdbad8, ffff888002bdbb98)
[ 12.486131][ T1]
[ 12.486194][ T1] The buggy address belongs to the physical page:
[ 12.486347][ T1] page: refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888002bdbc10 pfn:0x2bda
[ 12.486600][ T1] head: order:1 entire_mapcount:0 nr_pages_mapped:0 pincount:0
[ 12.486795][ T1] flags: 0x80000000000a40(workingset|slab|head|node=0|zone=1)
[ 12.486989][ T1] page_type: 0xffffffff()
[ 12.487088][ T1] raw: 0080000000000a40 ffff888001042c40 ffff888001040a88 ffff888001040a88
[ 12.487315][ T1] raw: ffff888002bdbc10 00000000001a0017 00000001ffffffff 0000000000000000
[ 12.487538][ T1] head: 0080000000000a40 ffff888001042c40 ffff888001040a88 ffff888001040a88
[ 12.487765][ T1] head: ffff888002bdbc10 00000000001a0017 00000001ffffffff 0000000000000000
[ 12.487992][ T1] head: 0080000000000001 ffffea00000af681 dead000000000122 00000000ffffffff
[ 12.488213][ T1] head: 0000000200000000 0000000000000000 00000000ffffffff 0000000000000000
[ 12.488436][ T1] page dumped because: kasan: bad access detected
[ 12.488590][ T1]
[ 12.488653][ T1] Memory state around the buggy address:
[ 12.488797][ T1] ffff888002bdb980: fc fc fc fc 00 00 00 00 00 00 00 00 00 00 00 00
[ 12.488986][ T1] ffff888002bdba00: 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc
[ 12.489168][ T1] >ffff888002bdba80: fc fc fc fc fc fc fc fc fc fc fc fa fb fb fb fb
[ 12.489353][ T1] ^
[ 12.489506][ T1] ffff888002bdbb00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 12.489688][ T1] ffff888002bdbb80: fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 12.489873][ T1] ==================================================================