Hi Cascardo,
Thanks for looking at the patch.
On 12/12/24 11:05 PM, Thadeu Lima de Souza Cascardo wrote:
On Thu, Dec 12, 2024 at 12:23:31PM +0530, Bhupesh wrote:
Once we are inside the 'ext4_xattr_delete_inode' function and trying
to delete the inode, the 'xattr_sem' should be unlocked.
We need trylock here to avoid false-positive warning from lockdep
about reclaim circular dependency.
This fixes the following KASAN reported issue:
==================================================================
BUG: KASAN: slab-use-after-free in ext4_xattr_inode_dec_ref_all+0xb8c/0xe90
Read of size 4 at addr ffff888012c120c4 by task repro/2065
CPU: 1 UID: 0 PID: 2065 Comm: repro Not tainted 6.13.0-rc2+ #11
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x1fd/0x300
? tcp_gro_dev_warn+0x260/0x260
? _printk+0xc0/0x100
? read_lock_is_recursive+0x10/0x10
? irq_work_queue+0x72/0xf0
? __virt_addr_valid+0x17b/0x4b0
print_address_description+0x78/0x390
print_report+0x107/0x1f0
? __virt_addr_valid+0x17b/0x4b0
? __virt_addr_valid+0x3ff/0x4b0
? __phys_addr+0xb5/0x160
? ext4_xattr_inode_dec_ref_all+0xb8c/0xe90
kasan_report+0xcc/0x100
? ext4_xattr_inode_dec_ref_all+0xb8c/0xe90
ext4_xattr_inode_dec_ref_all+0xb8c/0xe90
? ext4_xattr_delete_inode+0xd30/0xd30
? __ext4_journal_ensure_credits+0x5f0/0x5f0
? __ext4_journal_ensure_credits+0x2b/0x5f0
? inode_update_timestamps+0x410/0x410
ext4_xattr_delete_inode+0xb64/0xd30
? ext4_truncate+0xb70/0xdc0
? ext4_expand_extra_isize_ea+0x1d20/0x1d20
? __ext4_mark_inode_dirty+0x670/0x670
? ext4_journal_check_start+0x16f/0x240
? ext4_inode_is_fast_symlink+0x2f2/0x3a0
ext4_evict_inode+0xc8c/0xff0
? ext4_inode_is_fast_symlink+0x3a0/0x3a0
? do_raw_spin_unlock+0x53/0x8a0
? ext4_inode_is_fast_symlink+0x3a0/0x3a0
evict+0x4ac/0x950
? proc_nr_inodes+0x310/0x310
? trace_ext4_drop_inode+0xa2/0x220
? _raw_spin_unlock+0x1a/0x30
? iput+0x4cb/0x7e0
do_unlinkat+0x495/0x7c0
? try_break_deleg+0x120/0x120
? 0xffffffff81000000
? __check_object_size+0x15a/0x210
? strncpy_from_user+0x13e/0x250
? getname_flags+0x1dc/0x530
__x64_sys_unlinkat+0xc8/0xf0
do_syscall_64+0x65/0x110
entry_SYSCALL_64_after_hwframe+0x67/0x6f
RIP: 0033:0x434ffd
Code: 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 8
RSP: 002b:00007ffc50fa7b28 EFLAGS: 00000246 ORIG_RAX: 0000000000000107
RAX: ffffffffffffffda RBX: 00007ffc50fa7e18 RCX: 0000000000434ffd
RDX: 0000000000000000 RSI: 0000000020000240 RDI: 0000000000000005
RBP: 00007ffc50fa7be0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffc50fa7e08 R14: 00000000004bbf30 R15: 0000000000000001
</TASK>
The buggy address belongs to the object at ffff888012c12000
which belongs to the cache filp of size 360
The buggy address is located 196 bytes inside of
freed 360-byte region [ffff888012c12000, ffff888012c12168)
The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x12c12
head: order:1 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0x40(head|node=0|zone=0)
page_type: f5(slab)
raw: 0000000000000040 ffff888000ad7640 ffffea0000497a00 dead000000000004
raw: 0000000000000000 0000000000100010 00000001f5000000 0000000000000000
head: 0000000000000040 ffff888000ad7640 ffffea0000497a00 dead000000000004
head: 0000000000000000 0000000000100010 00000001f5000000 0000000000000000
head: 0000000000000001 ffffea00004b0481 ffffffffffffffff 0000000000000000
head: 0000000000000002 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff888012c11f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff888012c12000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888012c12080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888012c12100: fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc
ffff888012c12180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================
Reported-by: syzbot+b244bda78289b00204ed@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=b244bda78289b00204ed
Signed-off-by: Bhupesh <bhupesh@xxxxxxxxxx>
---
fs/ext4/xattr.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 7647e9f6e190..e1d29aa76165 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -2926,7 +2926,20 @@ int ext4_xattr_delete_inode(handle_t *handle, struct inode *inode,
struct ext4_iloc iloc = { .bh = NULL };
struct ext4_xattr_entry *entry;
struct inode *ea_inode;
- int error;
+ int error = 0;
+
+ /*
+ * We are the only ones holding inode reference. The xattr_sem should
+ * better be unlocked! We could as well just not acquire xattr_sem at
+ * all but this makes the code more futureproof. OTOH we need trylock
+ * here to avoid false-positive warning from lockdep about reclaim
+ * circular dependency.
+ */
+ if (WARN_ON_ONCE(!down_write_trylock(&EXT4_I(inode)->xattr_sem)))
+ return error;
+
+ if (!EXT4_I(inode)->i_file_acl)
+ goto cleanup;
This is ignoring the case where attributes are all in the inode, not in the
separate ACL block.
That's why this apparently fixes the problem. ext4_xattr_inode_dec_ref_all
is never called anymore.
Ok, I got your point, I will try to use existing inode checking
functions instead, to check for the 'attributes present in inode' case.
However, as we were discussing on irc, I think it would make sense still
to have the 'EXT4_I(inode)->xattr_sem' held while we delete the inode
inside '
ext4_xattr_delete_inode'. Please let me know in case you have other ideas.
I will send two patches then - one fixing the inode attribute issue and the other for holding the xattr_sem while we are inside the critical region deleting the inode.
Thanks,
Bhupesh
