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Date: Wed, 10 Aug 2022 15:20:48 +0800 From: Baokun Li <libaokun1@...wei.com> To: Lukas Czerner <lczerner@...hat.com> CC: <linux-ext4@...r.kernel.org>, <tytso@....edu>, <adilger.kernel@...ger.ca>, <jack@...e.cz>, <ritesh.list@...il.com>, <enwlinux@...il.com>, <linux-kernel@...r.kernel.org>, <yi.zhang@...wei.com>, <yebin10@...wei.com>, <yukuai3@...wei.com>, Baokun Li <libaokun1@...wei.com> Subject: Re: [PATCH] ext4: fix null-ptr-deref in ext4_write_info 在 2022/8/5 21:07, Lukas Czerner 写道: > On Fri, Aug 05, 2022 at 08:39:47PM +0800, Baokun Li wrote: >> I caught a null-ptr-deref bug as follows: >> ================================================================== >> KASAN: null-ptr-deref in range [0x0000000000000068-0x000000000000006f] >> CPU: 1 PID: 1589 Comm: umount Not tainted 5.10.0-02219-dirty #339 >> RIP: 0010:ext4_write_info+0x53/0x1b0 >> [...] >> Call Trace: >> dquot_writeback_dquots+0x341/0x9a0 >> ext4_sync_fs+0x19e/0x800 >> __sync_filesystem+0x83/0x100 >> sync_filesystem+0x89/0xf0 >> generic_shutdown_super+0x79/0x3e0 >> kill_block_super+0xa1/0x110 >> deactivate_locked_super+0xac/0x130 >> deactivate_super+0xb6/0xd0 >> cleanup_mnt+0x289/0x400 >> __cleanup_mnt+0x16/0x20 >> task_work_run+0x11c/0x1c0 >> exit_to_user_mode_prepare+0x203/0x210 >> syscall_exit_to_user_mode+0x5b/0x3a0 >> do_syscall_64+0x59/0x70 >> entry_SYSCALL_64_after_hwframe+0x44/0xa9 >> ================================================================== >> >> Above issue may happen as follows: >> ------------------------------------- >> exit_to_user_mode_prepare >> task_work_run >> __cleanup_mnt >> cleanup_mnt >> deactivate_super >> deactivate_locked_super >> kill_block_super >> generic_shutdown_super >> shrink_dcache_for_umount >> dentry = sb->s_root >> sb->s_root = NULL <--- Here set NULL >> sync_filesystem >> __sync_filesystem >> sb->s_op->sync_fs > ext4_sync_fs >> dquot_writeback_dquots >> sb->dq_op->write_info > ext4_write_info >> ext4_journal_start(d_inode(sb->s_root), EXT4_HT_QUOTA, 2) >> d_inode(sb->s_root) >> s_root->d_inode <--- Null pointer dereference >> >> To solve this problem, we use ext4_journal_start_sb directly >> to avoid s_root being used. > Are we syncing the file system after the superblock shutdown and getting > away with it? This does not look good. Do you have a reproducer? > > Thanks! > -Lukas Hi, Lukas! This problem is triggered by a pressure test when I reproduce another problem. So I didn't have the reproducer. I looked at the error stack code and found that it seems there is something wrong. Moreover, it's really weird to write code like "ext4_journal_start(d_inode(sb->s_root), ...)". >> Signed-off-by: Baokun Li <libaokun1@...wei.com> >> --- >> fs/ext4/super.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/fs/ext4/super.c b/fs/ext4/super.c >> index 9a66abcca1a8..0ce4565422f6 100644 >> --- a/fs/ext4/super.c >> +++ b/fs/ext4/super.c >> @@ -6653,7 +6653,7 @@ static int ext4_write_info(struct super_block *sb, int type) >> handle_t *handle; >> >> /* Data block + inode block */ >> - handle = ext4_journal_start(d_inode(sb->s_root), EXT4_HT_QUOTA, 2); >> + handle = ext4_journal_start_sb(sb, EXT4_HT_QUOTA, 2); >> if (IS_ERR(handle)) >> return PTR_ERR(handle); >> ret = dquot_commit_info(sb, type); >> -- >> 2.31.1 >> > . Thanks! -- With Best Regards, Baokun Li
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