[PATCH -next] ext4: Fix null-ptr-deref in '__ext4_journal_ensure_credits'
From: Ye Bin
Date: Fri Dec 24 2021 - 04:52:15 EST
We got issue as follows when run syzkaller test:
[ 1901.130043] EXT4-fs error (device vda): ext4_remount:5624: comm syz-executor.5: Abort forced by user
[ 1901.130901] Aborting journal on device vda-8.
[ 1901.131437] EXT4-fs error (device vda): ext4_journal_check_start:61: comm syz-executor.16: Detected aborted journal
[ 1901.131566] EXT4-fs error (device vda): ext4_journal_check_start:61: comm syz-executor.11: Detected aborted journal
[ 1901.132586] EXT4-fs error (device vda): ext4_journal_check_start:61: comm syz-executor.18: Detected aborted journal
[ 1901.132751] EXT4-fs error (device vda): ext4_journal_check_start:61: comm syz-executor.9: Detected aborted journal
[ 1901.136149] EXT4-fs error (device vda) in ext4_reserve_inode_write:6035: Journal has aborted
[ 1901.136837] EXT4-fs error (device vda): ext4_journal_check_start:61: comm syz-fuzzer: Detected aborted journal
[ 1901.136915] ==================================================================
[ 1901.138175] BUG: KASAN: null-ptr-deref in __ext4_journal_ensure_credits+0x74/0x140 [ext4]
[ 1901.138343] EXT4-fs error (device vda): ext4_journal_check_start:61: comm syz-executor.13: Detected aborted journal
[ 1901.138398] EXT4-fs error (device vda): ext4_journal_check_start:61: comm syz-executor.1: Detected aborted journal
[ 1901.138808] Read of size 8 at addr 0000000000000000 by task syz-executor.17/968
[ 1901.138817]
[ 1901.138852] EXT4-fs error (device vda): ext4_journal_check_start:61: comm syz-executor.30: Detected aborted journal
[ 1901.144779] CPU: 1 PID: 968 Comm: syz-executor.17 Not tainted 4.19.90-vhulk2111.1.0.h893.eulerosv2r10.aarch64+ #1
[ 1901.146479] Hardware name: linux,dummy-virt (DT)
[ 1901.147317] Call trace:
[ 1901.147552] dump_backtrace+0x0/0x2d8
[ 1901.147898] show_stack+0x28/0x38
[ 1901.148215] dump_stack+0xec/0x15c
[ 1901.148746] kasan_report+0x108/0x338
[ 1901.149207] __asan_load8+0x58/0xb0
[ 1901.149753] __ext4_journal_ensure_credits+0x74/0x140 [ext4]
[ 1901.150579] ext4_xattr_delete_inode+0xe4/0x700 [ext4]
[ 1901.151316] ext4_evict_inode+0x524/0xba8 [ext4]
[ 1901.151985] evict+0x1a4/0x378
[ 1901.152353] iput+0x310/0x428
[ 1901.152733] do_unlinkat+0x260/0x428
[ 1901.153056] __arm64_sys_unlinkat+0x6c/0xc0
[ 1901.153455] el0_svc_common+0xc8/0x320
[ 1901.153799] el0_svc_handler+0xf8/0x160
[ 1901.154265] el0_svc+0x10/0x218
[ 1901.154682] ==================================================================
This issue may happens like this:
Process1 Process2
ext4_evict_inode
ext4_journal_start
ext4_truncate
ext4_ind_truncate
ext4_free_branches
ext4_ind_truncate_ensure_credits
ext4_journal_ensure_credits_fn
ext4_journal_restart
handle->h_transaction = NULL;
mount -o remount,abort /mnt
-> trigger JBD abort
start_this_handle -> will return failed
ext4_xattr_delete_inode
ext4_journal_ensure_credits
ext4_journal_ensure_credits_fn
__ext4_journal_ensure_credits
jbd2_handle_buffer_credits
journal = handle->h_transaction->t_journal; ->null-ptr-deref
Now, indirect truncate process didn't handle error. To solve this issue
maybe simply add check handle is abort in '__ext4_journal_ensure_credits'
is enough, and i also think this is necessary.
Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx>
---
fs/ext4/ext4_jbd2.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c
index 6def7339056d..3477a16d08ae 100644
--- a/fs/ext4/ext4_jbd2.c
+++ b/fs/ext4/ext4_jbd2.c
@@ -162,6 +162,8 @@ int __ext4_journal_ensure_credits(handle_t *handle, int check_cred,
{
if (!ext4_handle_valid(handle))
return 0;
+ if (is_handle_aborted(handle))
+ return -EROFS;
if (jbd2_handle_buffer_credits(handle) >= check_cred &&
handle->h_revoke_credits >= revoke_cred)
return 0;
--
2.31.1