From: Ye Bin yebin10@huawei.com
commit c186f0887fe7061a35cebef024550ec33ef8fbd8 upstream.
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 Reviewed-by: Jan Kara jack@suse.cz Link: https://lore.kernel.org/r/20220324064816.1209985-1-yebin10@huawei.com Signed-off-by: Theodore Ts'o tytso@mit.edu Cc: stable@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/ext4/ext4.h | 4 ++++ fs/ext4/namei.c | 4 ++-- 2 files changed, 6 insertions(+), 2 deletions(-)
--- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -2267,6 +2267,10 @@ static inline int ext4_forced_shutdown(s * Structure of a directory entry */ #define EXT4_NAME_LEN 255 +/* + * Base length of the ext4 directory entry excluding the name length + */ +#define EXT4_BASE_DIR_LEN (sizeof(struct ext4_dir_entry_2) - EXT4_NAME_LEN)
struct ext4_dir_entry { __le32 inode; /* Inode number */ --- a/fs/ext4/namei.c +++ b/fs/ext4/namei.c @@ -1466,10 +1466,10 @@ int ext4_search_dir(struct buffer_head *
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 */