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[-next] ext4: fix use-after-free in ext4_search_dir

Message ID 20220323034304.3597652-1-yebin10@huawei.com
State Superseded
Headers show
Series [-next] ext4: fix use-after-free in ext4_search_dir | expand

Commit Message

yebin (H) March 23, 2022, 3:43 a.m. UTC
We got issue as follows:
EXT4-fs (loop0): mounted filesystem without journal. Opts: ,errors=continue
==================================================================
BUG: KASAN: use-after-free in ext4_search_dir fs/ext4/namei.c:1394 [inline]
BUG: KASAN: use-after-free in search_dirblock fs/ext4/namei.c:1199 [inline]
BUG: KASAN: use-after-free in __ext4_find_entry+0xdca/0x1210 fs/ext4/namei.c:1553
Read of size 1 at addr ffff8881317c3005 by task syz-executor117/2331

CPU: 1 PID: 2331 Comm: syz-executor117 Not tainted 5.10.0+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
Call Trace:
 __dump_stack lib/dump_stack.c:83 [inline]
 dump_stack+0x144/0x187 lib/dump_stack.c:124
 print_address_description+0x7d/0x630 mm/kasan/report.c:387
 __kasan_report+0x132/0x190 mm/kasan/report.c:547
 kasan_report+0x47/0x60 mm/kasan/report.c:564
 ext4_search_dir fs/ext4/namei.c:1394 [inline]
 search_dirblock fs/ext4/namei.c:1199 [inline]
 __ext4_find_entry+0xdca/0x1210 fs/ext4/namei.c:1553
 ext4_lookup_entry fs/ext4/namei.c:1622 [inline]
 ext4_lookup+0xb8/0x3a0 fs/ext4/namei.c:1690
 __lookup_hash+0xc5/0x190 fs/namei.c:1451
 do_rmdir+0x19e/0x310 fs/namei.c:3760
 do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x445e59
Code: 4d c7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 1b c7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fff2277fac8 EFLAGS: 00000246 ORIG_RAX: 0000000000000054
RAX: ffffffffffffffda RBX: 0000000000400280 RCX: 0000000000445e59
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000200000c0
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000002
R10: 00007fff2277f990 R11: 0000000000000246 R12: 0000000000000000
R13: 431bde82d7b634db R14: 0000000000000000 R15: 0000000000000000

The buggy address belongs to the page:
page:0000000048cd3304 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x1317c3
flags: 0x200000000000000()
raw: 0200000000000000 ffffea0004526588 ffffea0004528088 0000000000000000
raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881317c2f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8881317c2f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8881317c3000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff8881317c3080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8881317c3100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================

ext4_search_dir:
  ...
  de = (struct ext4_dir_entry_2 *)search_buf;
  dlimit = search_buf + buf_size;
  while ((char *) de < dlimit) {
  ...
    if ((char *) de + de->name_len <= dlimit &&
	 ext4_match(dir, fname, de)) {
	    ...
    }
  ...
    de_len = ext4_rec_len_from_disk(de->rec_len, dir->i_sb->s_blocksize);
    if (de_len <= 0)
      return -1;
    offset += de_len;
    de = (struct ext4_dir_entry_2 *) ((char *) de + de_len);
  }

Assume:
de=0xffff8881317c2fff
dlimit=0x0xffff8881317c3000

If read 'de->name_len' which address is 0xffff8881317c3005, obviously is
out of range, then will trigger use-after-free.
To solve this issue, 'dlimit' must reserve 8 bytes, as we will read
'de->name_len' to judge if '(char *) de + de->name_len' out of range.

Signed-off-by: Ye Bin <yebin10@huawei.com>
---
 fs/ext4/ext4.h  | 4 ++++
 fs/ext4/namei.c | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

Comments

Jan Kara March 23, 2022, 10:47 a.m. UTC | #1
On Wed 23-03-22 11:43:04, Ye Bin wrote:
> We got issue as follows:
> EXT4-fs (loop0): mounted filesystem without journal. Opts: ,errors=continue
> ==================================================================
> BUG: KASAN: use-after-free in ext4_search_dir fs/ext4/namei.c:1394 [inline]
> BUG: KASAN: use-after-free in search_dirblock fs/ext4/namei.c:1199 [inline]
> BUG: KASAN: use-after-free in __ext4_find_entry+0xdca/0x1210 fs/ext4/namei.c:1553
> Read of size 1 at addr ffff8881317c3005 by task syz-executor117/2331
> 
> CPU: 1 PID: 2331 Comm: syz-executor117 Not tainted 5.10.0+ #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
> Call Trace:
>  __dump_stack lib/dump_stack.c:83 [inline]
>  dump_stack+0x144/0x187 lib/dump_stack.c:124
>  print_address_description+0x7d/0x630 mm/kasan/report.c:387
>  __kasan_report+0x132/0x190 mm/kasan/report.c:547
>  kasan_report+0x47/0x60 mm/kasan/report.c:564
>  ext4_search_dir fs/ext4/namei.c:1394 [inline]
>  search_dirblock fs/ext4/namei.c:1199 [inline]
>  __ext4_find_entry+0xdca/0x1210 fs/ext4/namei.c:1553
>  ext4_lookup_entry fs/ext4/namei.c:1622 [inline]
>  ext4_lookup+0xb8/0x3a0 fs/ext4/namei.c:1690
>  __lookup_hash+0xc5/0x190 fs/namei.c:1451
>  do_rmdir+0x19e/0x310 fs/namei.c:3760
>  do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x445e59
> Code: 4d c7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 1b c7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007fff2277fac8 EFLAGS: 00000246 ORIG_RAX: 0000000000000054
> RAX: ffffffffffffffda RBX: 0000000000400280 RCX: 0000000000445e59
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000200000c0
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000002
> R10: 00007fff2277f990 R11: 0000000000000246 R12: 0000000000000000
> R13: 431bde82d7b634db R14: 0000000000000000 R15: 0000000000000000
> 
> The buggy address belongs to the page:
> page:0000000048cd3304 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x1317c3
> flags: 0x200000000000000()
> raw: 0200000000000000 ffffea0004526588 ffffea0004528088 0000000000000000
> raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8881317c2f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>  ffff8881317c2f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >ffff8881317c3000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>                    ^
>  ffff8881317c3080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>  ffff8881317c3100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ==================================================================
> 
> ext4_search_dir:
>   ...
>   de = (struct ext4_dir_entry_2 *)search_buf;
>   dlimit = search_buf + buf_size;
>   while ((char *) de < dlimit) {
>   ...
>     if ((char *) de + de->name_len <= dlimit &&
> 	 ext4_match(dir, fname, de)) {
> 	    ...
>     }
>   ...
>     de_len = ext4_rec_len_from_disk(de->rec_len, dir->i_sb->s_blocksize);
>     if (de_len <= 0)
>       return -1;
>     offset += de_len;
>     de = (struct ext4_dir_entry_2 *) ((char *) de + de_len);
>   }
> 
> Assume:
> de=0xffff8881317c2fff
> dlimit=0x0xffff8881317c3000
> 
> If read 'de->name_len' which address is 0xffff8881317c3005, obviously is
> out of range, then will trigger use-after-free.
> To solve this issue, 'dlimit' must reserve 8 bytes, as we will read
> 'de->name_len' to judge if '(char *) de + de->name_len' out of range.
> 
> Signed-off-by: Ye Bin <yebin10@huawei.com>

Oh, good catch.

> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 3f87cca49f0c..276683f7ab77 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -2273,6 +2273,10 @@ static inline int ext4_forced_shutdown(struct ext4_sb_info *sbi)
>   * Structure of a directory entry
>   */
>  #define EXT4_NAME_LEN 255
> +/*
> + * Base length of ext4_dir_entry_2 and ext4_dir_entry exclude name
> + */
> +#define EXT4_BASE_DIR_LEN 8

I'd rather use (sizeof(struct ext4_dir_entry_2) - EXT4_NAME_LEN) here...

>  struct ext4_dir_entry {
>  	__le32	inode;			/* Inode number */
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index e37da8d5cd0c..4739a5aa13aa 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -1465,7 +1465,7 @@ int ext4_search_dir(struct buffer_head *bh, char *search_buf, int buf_size,
>  	int de_len;
>  
>  	de = (struct ext4_dir_entry_2 *)search_buf;
> -	dlimit = search_buf + buf_size;
> +	dlimit = search_buf + buf_size - EXT4_BASE_DIR_LEN;
>  	while ((char *) de < dlimit) {
>  		/* this code is executed quadratically often */
>  		/* do minimal checking `by hand' */

This looks wrong because a bit later we use dlimit to verify
de+de->name_len and that can certainly go upto bufsize. You need to modify
only the condition in the while loop like:

  	while ((char *) de < dlimit - EXT4_BASE_DIR_LEN) {

									Honza
yebin (H) March 23, 2022, noon UTC | #2
On 2022/3/23 18:47, Jan Kara wrote:
> On Wed 23-03-22 11:43:04, Ye Bin wrote:
>> We got issue as follows:
>> EXT4-fs (loop0): mounted filesystem without journal. Opts: ,errors=continue
>> ==================================================================
>> BUG: KASAN: use-after-free in ext4_search_dir fs/ext4/namei.c:1394 [inline]
>> BUG: KASAN: use-after-free in search_dirblock fs/ext4/namei.c:1199 [inline]
>> BUG: KASAN: use-after-free in __ext4_find_entry+0xdca/0x1210 fs/ext4/namei.c:1553
>> Read of size 1 at addr ffff8881317c3005 by task syz-executor117/2331
>>
>> CPU: 1 PID: 2331 Comm: syz-executor117 Not tainted 5.10.0+ #1
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
>> Call Trace:
>>   __dump_stack lib/dump_stack.c:83 [inline]
>>   dump_stack+0x144/0x187 lib/dump_stack.c:124
>>   print_address_description+0x7d/0x630 mm/kasan/report.c:387
>>   __kasan_report+0x132/0x190 mm/kasan/report.c:547
>>   kasan_report+0x47/0x60 mm/kasan/report.c:564
>>   ext4_search_dir fs/ext4/namei.c:1394 [inline]
>>   search_dirblock fs/ext4/namei.c:1199 [inline]
>>   __ext4_find_entry+0xdca/0x1210 fs/ext4/namei.c:1553
>>   ext4_lookup_entry fs/ext4/namei.c:1622 [inline]
>>   ext4_lookup+0xb8/0x3a0 fs/ext4/namei.c:1690
>>   __lookup_hash+0xc5/0x190 fs/namei.c:1451
>>   do_rmdir+0x19e/0x310 fs/namei.c:3760
>>   do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46
>>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
>> RIP: 0033:0x445e59
>> Code: 4d c7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 1b c7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
>> RSP: 002b:00007fff2277fac8 EFLAGS: 00000246 ORIG_RAX: 0000000000000054
>> RAX: ffffffffffffffda RBX: 0000000000400280 RCX: 0000000000445e59
>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000200000c0
>> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000002
>> R10: 00007fff2277f990 R11: 0000000000000246 R12: 0000000000000000
>> R13: 431bde82d7b634db R14: 0000000000000000 R15: 0000000000000000
>>
>> The buggy address belongs to the page:
>> page:0000000048cd3304 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x1317c3
>> flags: 0x200000000000000()
>> raw: 0200000000000000 ffffea0004526588 ffffea0004528088 0000000000000000
>> raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
>> page dumped because: kasan: bad access detected
>>
>> Memory state around the buggy address:
>>   ffff8881317c2f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>   ffff8881317c2f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>> ffff8881317c3000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>>                     ^
>>   ffff8881317c3080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>>   ffff8881317c3100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>> ==================================================================
>>
>> ext4_search_dir:
>>    ...
>>    de = (struct ext4_dir_entry_2 *)search_buf;
>>    dlimit = search_buf + buf_size;
>>    while ((char *) de < dlimit) {
>>    ...
>>      if ((char *) de + de->name_len <= dlimit &&
>> 	 ext4_match(dir, fname, de)) {
>> 	    ...
>>      }
>>    ...
>>      de_len = ext4_rec_len_from_disk(de->rec_len, dir->i_sb->s_blocksize);
>>      if (de_len <= 0)
>>        return -1;
>>      offset += de_len;
>>      de = (struct ext4_dir_entry_2 *) ((char *) de + de_len);
>>    }
>>
>> Assume:
>> de=0xffff8881317c2fff
>> dlimit=0x0xffff8881317c3000
>>
>> If read 'de->name_len' which address is 0xffff8881317c3005, obviously is
>> out of range, then will trigger use-after-free.
>> To solve this issue, 'dlimit' must reserve 8 bytes, as we will read
>> 'de->name_len' to judge if '(char *) de + de->name_len' out of range.
>>
>> Signed-off-by: Ye Bin <yebin10@huawei.com>
> Oh, good catch.
>
>> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
>> index 3f87cca49f0c..276683f7ab77 100644
>> --- a/fs/ext4/ext4.h
>> +++ b/fs/ext4/ext4.h
>> @@ -2273,6 +2273,10 @@ static inline int ext4_forced_shutdown(struct ext4_sb_info *sbi)
>>    * Structure of a directory entry
>>    */
>>   #define EXT4_NAME_LEN 255
>> +/*
>> + * Base length of ext4_dir_entry_2 and ext4_dir_entry exclude name
>> + */
>> +#define EXT4_BASE_DIR_LEN 8
> I'd rather use (sizeof(struct ext4_dir_entry_2) - EXT4_NAME_LEN) here...
>
>>   struct ext4_dir_entry {
>>   	__le32	inode;			/* Inode number */
>> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
>> index e37da8d5cd0c..4739a5aa13aa 100644
>> --- a/fs/ext4/namei.c
>> +++ b/fs/ext4/namei.c
>> @@ -1465,7 +1465,7 @@ int ext4_search_dir(struct buffer_head *bh, char *search_buf, int buf_size,
>>   	int de_len;
>>   
>>   	de = (struct ext4_dir_entry_2 *)search_buf;
>> -	dlimit = search_buf + buf_size;
>> +	dlimit = search_buf + buf_size - EXT4_BASE_DIR_LEN;
>>   	while ((char *) de < dlimit) {
>>   		/* this code is executed quadratically often */
>>   		/* do minimal checking `by hand' */
> This looks wrong because a bit later we use dlimit to verify
> de+de->name_len and that can certainly go upto bufsize. You need to modify
> only the condition in the while loop like:
>
>    	while ((char *) de < dlimit - EXT4_BASE_DIR_LEN) {
>
> 									Honza
I think  'dlimit' also need to minus EXT4_BASE_DIR_LEN when verify 
'de+de->name_len' .
Assume:
de = 0xffff8881317c2ff7
dlimit = 0x0xffff8881317c3000
de->name_len = 8

=>
de + de->name_len = 0xffff8881317c2fff  ( <= dlimit=0x0xffff8881317c3000)
de->name = 'de' address  + EXT4_BASE_DIR_LEN  = 0xffff8881317c2ff7 + 8 = 
0xffff8881317c2fff
If we read 8 bytes form 0xffff8881317c2fff will read out of range.
Jan Kara March 23, 2022, 1:36 p.m. UTC | #3
On Wed 23-03-22 20:00:55, yebin wrote:
> On 2022/3/23 18:47, Jan Kara wrote:
> > On Wed 23-03-22 11:43:04, Ye Bin wrote:
> > > We got issue as follows:
> > > EXT4-fs (loop0): mounted filesystem without journal. Opts: ,errors=continue
> > > ==================================================================
> > > BUG: KASAN: use-after-free in ext4_search_dir fs/ext4/namei.c:1394 [inline]
> > > BUG: KASAN: use-after-free in search_dirblock fs/ext4/namei.c:1199 [inline]
> > > BUG: KASAN: use-after-free in __ext4_find_entry+0xdca/0x1210 fs/ext4/namei.c:1553
> > > Read of size 1 at addr ffff8881317c3005 by task syz-executor117/2331
> > > 
> > > CPU: 1 PID: 2331 Comm: syz-executor117 Not tainted 5.10.0+ #1
> > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
> > > Call Trace:
> > >   __dump_stack lib/dump_stack.c:83 [inline]
> > >   dump_stack+0x144/0x187 lib/dump_stack.c:124
> > >   print_address_description+0x7d/0x630 mm/kasan/report.c:387
> > >   __kasan_report+0x132/0x190 mm/kasan/report.c:547
> > >   kasan_report+0x47/0x60 mm/kasan/report.c:564
> > >   ext4_search_dir fs/ext4/namei.c:1394 [inline]
> > >   search_dirblock fs/ext4/namei.c:1199 [inline]
> > >   __ext4_find_entry+0xdca/0x1210 fs/ext4/namei.c:1553
> > >   ext4_lookup_entry fs/ext4/namei.c:1622 [inline]
> > >   ext4_lookup+0xb8/0x3a0 fs/ext4/namei.c:1690
> > >   __lookup_hash+0xc5/0x190 fs/namei.c:1451
> > >   do_rmdir+0x19e/0x310 fs/namei.c:3760
> > >   do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46
> > >   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > > RIP: 0033:0x445e59
> > > Code: 4d c7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 1b c7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> > > RSP: 002b:00007fff2277fac8 EFLAGS: 00000246 ORIG_RAX: 0000000000000054
> > > RAX: ffffffffffffffda RBX: 0000000000400280 RCX: 0000000000445e59
> > > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000200000c0
> > > RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000002
> > > R10: 00007fff2277f990 R11: 0000000000000246 R12: 0000000000000000
> > > R13: 431bde82d7b634db R14: 0000000000000000 R15: 0000000000000000
> > > 
> > > The buggy address belongs to the page:
> > > page:0000000048cd3304 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x1317c3
> > > flags: 0x200000000000000()
> > > raw: 0200000000000000 ffffea0004526588 ffffea0004528088 0000000000000000
> > > raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
> > > page dumped because: kasan: bad access detected
> > > 
> > > Memory state around the buggy address:
> > >   ffff8881317c2f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > >   ffff8881317c2f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > > > ffff8881317c3000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > >                     ^
> > >   ffff8881317c3080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > >   ffff8881317c3100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > > ==================================================================
> > > 
> > > ext4_search_dir:
> > >    ...
> > >    de = (struct ext4_dir_entry_2 *)search_buf;
> > >    dlimit = search_buf + buf_size;
> > >    while ((char *) de < dlimit) {
> > >    ...
> > >      if ((char *) de + de->name_len <= dlimit &&
> > > 	 ext4_match(dir, fname, de)) {
> > > 	    ...
> > >      }
> > >    ...
> > >      de_len = ext4_rec_len_from_disk(de->rec_len, dir->i_sb->s_blocksize);
> > >      if (de_len <= 0)
> > >        return -1;
> > >      offset += de_len;
> > >      de = (struct ext4_dir_entry_2 *) ((char *) de + de_len);
> > >    }
> > > 
> > > Assume:
> > > de=0xffff8881317c2fff
> > > dlimit=0x0xffff8881317c3000
> > > 
> > > If read 'de->name_len' which address is 0xffff8881317c3005, obviously is
> > > out of range, then will trigger use-after-free.
> > > To solve this issue, 'dlimit' must reserve 8 bytes, as we will read
> > > 'de->name_len' to judge if '(char *) de + de->name_len' out of range.
> > > 
> > > Signed-off-by: Ye Bin <yebin10@huawei.com>
> > Oh, good catch.
> > 
> > > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> > > index 3f87cca49f0c..276683f7ab77 100644
> > > --- a/fs/ext4/ext4.h
> > > +++ b/fs/ext4/ext4.h
> > > @@ -2273,6 +2273,10 @@ static inline int ext4_forced_shutdown(struct ext4_sb_info *sbi)
> > >    * Structure of a directory entry
> > >    */
> > >   #define EXT4_NAME_LEN 255
> > > +/*
> > > + * Base length of ext4_dir_entry_2 and ext4_dir_entry exclude name
> > > + */
> > > +#define EXT4_BASE_DIR_LEN 8
> > I'd rather use (sizeof(struct ext4_dir_entry_2) - EXT4_NAME_LEN) here...
> > 
> > >   struct ext4_dir_entry {
> > >   	__le32	inode;			/* Inode number */
> > > diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> > > index e37da8d5cd0c..4739a5aa13aa 100644
> > > --- a/fs/ext4/namei.c
> > > +++ b/fs/ext4/namei.c
> > > @@ -1465,7 +1465,7 @@ int ext4_search_dir(struct buffer_head *bh, char *search_buf, int buf_size,
> > >   	int de_len;
> > >   	de = (struct ext4_dir_entry_2 *)search_buf;
> > > -	dlimit = search_buf + buf_size;
> > > +	dlimit = search_buf + buf_size - EXT4_BASE_DIR_LEN;
> > >   	while ((char *) de < dlimit) {
> > >   		/* this code is executed quadratically often */
> > >   		/* do minimal checking `by hand' */
> > This looks wrong because a bit later we use dlimit to verify
> > de+de->name_len and that can certainly go upto bufsize. You need to modify
> > only the condition in the while loop like:
> > 
> >    	while ((char *) de < dlimit - EXT4_BASE_DIR_LEN) {
> > 
> > 									Honza
> I think  'dlimit' also need to minus EXT4_BASE_DIR_LEN when verify
> 'de+de->name_len' .
> Assume:
> de = 0xffff8881317c2ff7
> dlimit = 0x0xffff8881317c3000
> de->name_len = 8
> 
> =>
> de + de->name_len = 0xffff8881317c2fff  ( <= dlimit=0x0xffff8881317c3000)
> de->name = 'de' address  + EXT4_BASE_DIR_LEN  = 0xffff8881317c2ff7 + 8 =
> 0xffff8881317c2fff
> If we read 8 bytes form 0xffff8881317c2fff will read out of range.

Ah, I see. Well, I'd rather modify the condition to look like:

                if (de->name + de->name_len <= dlimit &&
                    ext4_match(dir, fname, de)) {

Because that expresses better what we are checking...

								Honza
diff mbox series

Patch

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 3f87cca49f0c..276683f7ab77 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2273,6 +2273,10 @@  static inline int ext4_forced_shutdown(struct ext4_sb_info *sbi)
  * Structure of a directory entry
  */
 #define EXT4_NAME_LEN 255
+/*
+ * Base length of ext4_dir_entry_2 and ext4_dir_entry exclude name
+ */
+#define EXT4_BASE_DIR_LEN 8
 
 struct ext4_dir_entry {
 	__le32	inode;			/* Inode number */
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index e37da8d5cd0c..4739a5aa13aa 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1465,7 +1465,7 @@  int ext4_search_dir(struct buffer_head *bh, char *search_buf, int buf_size,
 	int de_len;
 
 	de = (struct ext4_dir_entry_2 *)search_buf;
-	dlimit = search_buf + buf_size;
+	dlimit = search_buf + buf_size - EXT4_BASE_DIR_LEN;
 	while ((char *) de < dlimit) {
 		/* this code is executed quadratically often */
 		/* do minimal checking `by hand' */