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Below is the synchronization issue between unmount and kjournald2
contexts, which results into use after free issue in kjournald2().
Fix this issue by using journal->j_state_lock to synchronize the
wait_event() done in journal_kill_thread() and the wake_up() done
in kjournald2().
TASK 1:
umount cmd:
|--jbd2_journal_destroy() {
|--journal_kill_thread() {
write_lock(&journal->j_state_lock);
journal->j_flags |= JBD2_UNMOUNT;
...
write_unlock(&journal->j_state_lock);
wake_up(&journal->j_wait_commit); TASK 2 wakes up here:
kjournald2() {
...
checks JBD2_UNMOUNT flag and calls goto end-loop;
...
end_loop:
write_unlock(&journal->j_state_lock);
journal->j_task = NULL; --> If this thread gets
pre-empted here, then TASK 1 wait_event will
exit even before this thread is completely
done.
wait_event(journal->j_wait_done_commit, journal->j_task == NULL);
...
write_lock(&journal->j_state_lock);
write_unlock(&journal->j_state_lock);
}
|--kfree(journal);
}
}
wake_up(&journal->j_wait_done_commit); --> this step
now results into use after free issue.
}
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
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| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
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| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.