Re: [PATCH] udf: Fix a slab-out-of-bounds write bug in udf_write_aext()

From: Jan Kara
Date: Thu Nov 10 2022 - 06:53:07 EST

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In reply to: Peng Zhang: "[PATCH] udf: Fix a slab-out-of-bounds write bug in udf_write_aext()"
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Hello!

On Thu 10-11-22 01:40:52, Peng Zhang wrote:
> From: ZhangPeng <zhangpeng362@xxxxxxxxxx>
>
> Syzbot reported a slab-out-of-bounds write bug:
>
> loop0: detected capacity change from 0 to 2048
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in udf_write_aext+0x8bc/0x8f0
> fs/udf/inode.c:2103
> Write of size 4 at addr ffff8880777c63f8 by task syz-executor216/3611
>
> CPU: 0 PID: 3611 Comm: syz-executor216 Not tainted
> 6.0.0-syzkaller-09589-g55be6084c8e0 #0
> Hardware name: Google Compute Engine/Google Compute Engine, BIOS
> Google 09/22/2022
> Call Trace:
> <TASK>
> __dump_stack lib/dump_stack.c:88 [inline]
> dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
> print_address_description mm/kasan/report.c:317 [inline]
> print_report.cold+0x2ba/0x719 mm/kasan/report.c:433
> kasan_report+0xb1/0x1e0 mm/kasan/report.c:495
> udf_write_aext+0x8bc/0x8f0 fs/udf/inode.c:2103
> udf_add_entry+0xd03/0x2ac0 fs/udf/namei.c:482
> udf_mkdir+0x145/0x650 fs/udf/namei.c:681
> vfs_mkdir+0x489/0x740 fs/namei.c:4013
> do_mkdirat+0x28c/0x310 fs/namei.c:4038
> __do_sys_mkdir fs/namei.c:4058 [inline]
> __se_sys_mkdir fs/namei.c:4056 [inline]
> __x64_sys_mkdir+0xf2/0x140 fs/namei.c:4056
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7fef3beda479
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89
> f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01
> f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffe952d4e28 EFLAGS: 00000246 ORIG_RAX: 0000000000000053
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fef3beda479
> RDX: 00007fef3be986e3 RSI: 0000000000000000 RDI: 0000000020000000
> RBP: 00007fef3be999b0 R08: 00007ffe952d4d10 R09: 0000000000000000
> R10: 00007ffe952d4cf0 R11: 0000000000000246 R12: 00007fef3be99a40
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> </TASK>
>
> Allocated by task 3611:
> kasan_save_stack+0x1e/0x40 mm/kasan/common.c:38
> kasan_set_track mm/kasan/common.c:45 [inline]
> set_alloc_info mm/kasan/common.c:437 [inline]
> ____kasan_kmalloc mm/kasan/common.c:516 [inline]
> ____kasan_kmalloc mm/kasan/common.c:475 [inline]
> __kasan_kmalloc+0xa9/0xd0 mm/kasan/common.c:525
> kmalloc include/linux/slab.h:600 [inline]
> kmalloc_array include/linux/slab.h:639 [inline]
> kcalloc include/linux/slab.h:671 [inline]
> udf_process_sequence+0xe9/0x4470 fs/udf/super.c:1689
> udf_load_sequence fs/udf/super.c:1813 [inline]
> udf_check_anchor_block+0x44b/0x640 fs/udf/super.c:1852
> udf_scan_anchors+0x1b3/0x6d0 fs/udf/super.c:1885
> udf_find_anchor fs/udf/super.c:1941 [inline]
> udf_load_vrs+0x27b/0xbe0 fs/udf/super.c:2006
> udf_fill_super+0x859/0x1a40 fs/udf/super.c:2184
> mount_bdev+0x34d/0x410 fs/super.c:1400
> legacy_get_tree+0x105/0x220 fs/fs_context.c:610
> vfs_get_tree+0x89/0x2f0 fs/super.c:1530
> do_new_mount fs/namespace.c:3040 [inline]
> path_mount+0x1326/0x1e20 fs/namespace.c:3370
> do_mount fs/namespace.c:3383 [inline]
> __do_sys_mount fs/namespace.c:3591 [inline]
> __se_sys_mount fs/namespace.c:3568 [inline]
> __x64_sys_mount+0x27f/0x300 fs/namespace.c:3568
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> Freed by task 3611:
> kasan_save_stack+0x1e/0x40 mm/kasan/common.c:38
> kasan_set_track+0x21/0x30 mm/kasan/common.c:45
> kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:370
> ____kasan_slab_free mm/kasan/common.c:367 [inline]
> ____kasan_slab_free+0x166/0x1c0 mm/kasan/common.c:329
> kasan_slab_free include/linux/kasan.h:200 [inline]
> slab_free_hook mm/slub.c:1759 [inline]
> slab_free_freelist_hook+0x8b/0x1c0 mm/slub.c:1785
> slab_free mm/slub.c:3539 [inline]
> kfree+0xe2/0x580 mm/slub.c:4567
> udf_process_sequence+0x421/0x4470 fs/udf/super.c:1781
> udf_load_sequence fs/udf/super.c:1813 [inline]
> udf_check_anchor_block+0x44b/0x640 fs/udf/super.c:1852
> udf_scan_anchors+0x1b3/0x6d0 fs/udf/super.c:1885
> udf_find_anchor fs/udf/super.c:1941 [inline]
> udf_load_vrs+0x27b/0xbe0 fs/udf/super.c:2006
> udf_fill_super+0x859/0x1a40 fs/udf/super.c:2184
> mount_bdev+0x34d/0x410 fs/super.c:1400
> legacy_get_tree+0x105/0x220 fs/fs_context.c:610
> vfs_get_tree+0x89/0x2f0 fs/super.c:1530
> do_new_mount fs/namespace.c:3040 [inline]
> path_mount+0x1326/0x1e20 fs/namespace.c:3370
> do_mount fs/namespace.c:3383 [inline]
> __do_sys_mount fs/namespace.c:3591 [inline]
> __se_sys_mount fs/namespace.c:3568 [inline]
> __x64_sys_mount+0x27f/0x300 fs/namespace.c:3568
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> The buggy address belongs to the object at ffff8880777c6000
> which belongs to the cache kmalloc-512 of size 512
> The buggy address is located 504 bytes to the right of
> 512-byte region [ffff8880777c6000, ffff8880777c6200)
>
> The buggy address belongs to the physical page:
> page:ffffea0001ddf100 refcount:1 mapcount:0 mapping:0000000000000000
> index:0x0 pfn:0x777c4
> head:ffffea0001ddf100 order:2 compound_mapcount:0 compound_pincount:0
> flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
> raw: 00fff00000010200 0000000000000000 dead000000000001 ffff888011841c80
> raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 2, migratetype Unmovable, gfp_mask
> pid 2972, tgid 2972 (udevadm), ts 11705893480, free_ts 9906278250
> prep_new_page mm/page_alloc.c:2532 [inline]
> get_page_from_freelist+0x109b/0x2ce0 mm/page_alloc.c:4283
> __alloc_pages+0x1c7/0x510 mm/page_alloc.c:5549
> alloc_pages+0x1a6/0x270 mm/mempolicy.c:2270
> alloc_slab_page mm/slub.c:1829 [inline]
> allocate_slab+0x27e/0x3d0 mm/slub.c:1974
> new_slab mm/slub.c:2034 [inline]
> ___slab_alloc+0x84f/0xe80 mm/slub.c:3036
> __slab_alloc.constprop.0+0x4d/0xa0 mm/slub.c:3123
> slab_alloc_node mm/slub.c:3214 [inline]
> slab_alloc mm/slub.c:3256 [inline]
> kmem_cache_alloc_trace+0x323/0x3e0 mm/slub.c:3287
> kmalloc include/linux/slab.h:600 [inline]
> kzalloc include/linux/slab.h:733 [inline]
> kernfs_fop_open+0x31a/0xec0 fs/kernfs/file.c:666
> do_dentry_open+0x6cc/0x13f0 fs/open.c:882
> do_open fs/namei.c:3557 [inline]
> path_openat+0x1c92/0x28f0 fs/namei.c:3691
> do_filp_open+0x1b6/0x400 fs/namei.c:3718
> do_sys_openat2+0x16d/0x4c0 fs/open.c:1310
> do_sys_open fs/open.c:1326 [inline]
> __do_sys_openat fs/open.c:1342 [inline]
> __se_sys_openat fs/open.c:1337 [inline]
> __x64_sys_openat+0x13f/0x1f0 fs/open.c:1337
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
> page last free stack trace:
> reset_page_owner include/linux/page_owner.h:24 [inline]
> free_pages_prepare mm/page_alloc.c:1449 [inline]
> free_pcp_prepare+0x5e4/0xd20 mm/page_alloc.c:1499
> free_unref_page_prepare mm/page_alloc.c:3380 [inline]
> free_unref_page+0x19/0x4d0 mm/page_alloc.c:3476
> free_contig_range+0xb1/0x180 mm/page_alloc.c:9457
> destroy_args+0xa8/0x646 mm/debug_vm_pgtable.c:1031
> debug_vm_pgtable+0x2945/0x29d6 mm/debug_vm_pgtable.c:1354
> do_one_initcall+0xfe/0x650 init/main.c:1296
> do_initcall_level init/main.c:1369 [inline]
> do_initcalls init/main.c:1385 [inline]
> do_basic_setup init/main.c:1404 [inline]
> kernel_init_freeable+0x6b1/0x73a init/main.c:1623
> kernel_init+0x1a/0x1d0 init/main.c:1512
> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
>
> Memory state around the buggy address:
> ffff8880777c6280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8880777c6300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >ffff8880777c6380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ^
> ffff8880777c6400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffff8880777c6480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ==================================================================
>
> Writing to the address ptr will cause an out-of-bounds bug if the inode
> allocation type is ICBTAG_FLAG_AD_SHORT (or ICBTAG_FLAG_AD_LONG), the
> buffer head pointer is NULL, and iinfo->i_lenEAttr is 0. In this case,
> the address ptr is iinfo->i_data - sizeof(struct short_ad), and the
> out-of-bounds offset is the size of struct short_ad. This can be fixed
> by adding the size of struct short_ad (or struct long_ad) to the address
> ptr.
>
> Reported-by: syzbot+908340a8367281960537@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 2c948b3f86e5 ("udf: Avoid IO in udf_clear_inode")
> Signed-off-by: ZhangPeng <zhangpeng362@xxxxxxxxxx>

Thanks for the fix! So do I understand correctly that in this case the
inode has type ICBTAG_FLAG_AD_SHORT and its size is 0 as well? Then I can
see how what you describe is happening. But the fix is actually wrong, it
will lead to writing extent to a wrong place in most cases. The problem
rather is that in this particular case in udf_add_entry() epos.offset
should not be decremented before calling udf_write_aext(). But when it
should / should not be decremented is really messy. It needs a broader look
and cleaning up...

Honza

> ---
> fs/udf/inode.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/fs/udf/inode.c b/fs/udf/inode.c
> index 8d06daed549f..abb3257b4c74 100644
> --- a/fs/udf/inode.c
> +++ b/fs/udf/inode.c
> @@ -2090,10 +2090,15 @@ void udf_write_aext(struct inode *inode, struct extent_position *epos,
> struct long_ad *lad;
> struct udf_inode_info *iinfo = UDF_I(inode);
>
> - if (!epos->bh)
> + if (!epos->bh) {
> ptr = iinfo->i_data + epos->offset -
> udf_file_entry_alloc_offset(inode) +
> iinfo->i_lenEAttr;
> + if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_SHORT)
> + ptr = ptr + sizeof(struct short_ad);
> + else if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_LONG)
> + ptr = ptr + sizeof(struct long_ad);
> + }
> else
> ptr = epos->bh->b_data + epos->offset;
>
> --
> 2.25.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR

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