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Message-ID: <20220324115120.p6uaoofizgwjazbl@quack3.lan> Date: Thu, 24 Mar 2022 12:51:20 +0100 From: Jan Kara <jack@...e.cz> To: Ye Bin <yebin10@...wei.com> Cc: tytso@....edu, adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org, jack@...e.cz, lczerner@...hat.com Subject: Re: [PATCH -next v2] ext4: fix use-after-free in ext4_search_dir On Thu 24-03-22 14:48:16, 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@...wei.com> Looks good. Thanks. Feel free to add: Reviewed-by: Jan Kara <jack@...e.cz> Honza > --- > fs/ext4/ext4.h | 4 ++++ > fs/ext4/namei.c | 4 ++-- > 2 files changed, 6 insertions(+), 2 deletions(-) > > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h > index 3f87cca49f0c..ea49cf5d70a9 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 (sizeof(struct ext4_dir_entry_2) - EXT4_NAME_LEN) > > struct ext4_dir_entry { > __le32 inode; /* Inode number */ > diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c > index e37da8d5cd0c..767b4bfe39c3 100644 > --- a/fs/ext4/namei.c > +++ b/fs/ext4/namei.c > @@ -1466,10 +1466,10 @@ int ext4_search_dir(struct buffer_head *bh, char *search_buf, int buf_size, > > de = (struct ext4_dir_entry_2 *)search_buf; > dlimit = search_buf + buf_size; > - while ((char *) de < dlimit) { > + while ((char *) de < dlimit - EXT4_BASE_DIR_LEN) { > /* this code is executed quadratically often */ > /* do minimal checking `by hand' */ > - if ((char *) de + de->name_len <= dlimit && > + if (de->name + de->name_len <= dlimit && > ext4_match(dir, fname, de)) { > /* found a match - just to be sure, do > * a full check */ > -- > 2.31.1 > -- Jan Kara <jack@...e.com> SUSE Labs, CR
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