Re: [PATCH -next] ext4: Fix null-ptr-deref in '__ext4_journal_ensure_credits'

[Jan Kara <jack@suse.cz>]

On Fri 24-12-21 18:03:41, Ye Bin wrote:
> 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@huawei.com>

Thanks for the report and the analysis! The fix looks good. Feel free to
add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza


> 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;


-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR