Commit 61bb4a1c authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

ext4: fix possible UAF when remounting r/o a mmp-protected file system 

After commit 618f0031 ("ext4: fix memory leak in
ext4_fill_super"), after the file system is remounted read-only, there
is a race where the kmmpd thread can exit, causing sbi->s_mmp_tsk to
point at freed memory, which the call to ext4_stop_mmpd() can trip
over.

Fix this by only allowing kmmpd() to exit when it is stopped via
ext4_stop_mmpd().

Link: https://lore.kernel.org/r/20210707002433.3719773-1-tytso@mit.edu


Reported-by: default avatarYe Bin <yebin10@huawei.com>
Bug-Report-Link: <20210629143603.2166962-1-yebin10@huawei.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
parent cd84bbba

fs/ext4/mmp.c

+15 −16
Original line number Diff line number Diff line
@@ -156,7 +156,12 @@ static int kmmpd(void *data) 
	memcpy(mmp->mmp_nodename, init_utsname()->nodename,

	       sizeof(mmp->mmp_nodename));



	while (!kthread_should_stop()) {

	while (!kthread_should_stop() && !sb_rdonly(sb)) {

		if (!ext4_has_feature_mmp(sb)) {

			ext4_warning(sb, "kmmpd being stopped since MMP feature"

				     " has been disabled.");

			goto wait_to_exit;

		}

		if (++seq > EXT4_MMP_SEQ_MAX)

			seq = 1;
@@ -177,16 +182,6 @@ static int kmmpd(void *data) 
			failed_writes++;

		}



		if (!(le32_to_cpu(es->s_feature_incompat) &

		    EXT4_FEATURE_INCOMPAT_MMP)) {

			ext4_warning(sb, "kmmpd being stopped since MMP feature"

				     " has been disabled.");

			goto exit_thread;

		}



		if (sb_rdonly(sb))

			break;



		diff = jiffies - last_update_time;

		if (diff < mmp_update_interval * HZ)

			schedule_timeout_interruptible(mmp_update_interval *
@@ -207,7 +202,7 @@ static int kmmpd(void *data) 
				ext4_error_err(sb, -retval,

					       "error reading MMP data: %d",

					       retval);

				goto exit_thread;

				goto wait_to_exit;

			}



			mmp_check = (struct mmp_struct *)(bh_check->b_data);
@@ -221,7 +216,7 @@ static int kmmpd(void *data) 
				ext4_error_err(sb, EBUSY, "abort");

				put_bh(bh_check);

				retval = -EBUSY;

				goto exit_thread;

				goto wait_to_exit;

			}

			put_bh(bh_check);

		}
@@ -244,7 +239,13 @@ static int kmmpd(void *data) 


	retval = write_mmp_block(sb, bh);



exit_thread:

wait_to_exit:

	while (!kthread_should_stop()) {

		set_current_state(TASK_INTERRUPTIBLE);

		if (!kthread_should_stop())

			schedule();

	}

	set_current_state(TASK_RUNNING);

	return retval;

}
@@ -391,5 +392,3 @@ int ext4_multi_mount_protect(struct super_block *sb, 
	brelse(bh);

	return 1;

}

fs/ext4/super.c

+5 −1
Original line number Diff line number Diff line
@@ -5993,7 +5993,6 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data) 
				 */

				ext4_mark_recovery_complete(sb, es);

			}

			ext4_stop_mmpd(sbi);

		} else {

			/* Make sure we can mount this feature set readwrite */

			if (ext4_has_feature_readonly(sb) ||
@@ -6107,6 +6106,9 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data) 
	if (!test_opt(sb, BLOCK_VALIDITY) && sbi->s_system_blks)

		ext4_release_system_zone(sb);



	if (!ext4_has_feature_mmp(sb) || sb_rdonly(sb))

		ext4_stop_mmpd(sbi);



	/*

	 * Some options can be enabled by ext4 and/or by VFS mount flag

	 * either way we need to make sure it matches in both *flags and
@@ -6140,6 +6142,8 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data) 
	for (i = 0; i < EXT4_MAXQUOTAS; i++)

		kfree(to_free[i]);

#endif

	if (!ext4_has_feature_mmp(sb) || sb_rdonly(sb))

		ext4_stop_mmpd(sbi);

	kfree(orig_data);

	return err;

}