In the Linux kernel, the following vulnerability has been resolved:
ext4: fix memory leak in ext4_fill_super
Buffer head references must be released before calling kill_bdev();
otherwise the buffer head (and its page referenced by b_data) will not
be freed by kill_bdev, and subsequently that bh will be leaked.
If blocksizes differ, sb_set_blocksize() will kill current buffers and
page cache by using kill_bdev(). And then super block will be reread
again but using correct blocksize this time. sb_set_blocksize() didn't
fully free superblock page and buffer head, and being busy, they were
not freed and instead leaked.
This can easily be reproduced by calling an infinite loop of:
systemctl start <ext4_on_lvm>.mount, and
systemctl stop <ext4_on_lvm>.mount
... since systemd creates a cgroup for each slice which it mounts, and
the bh leak get amplified by a dying memory cgroup that also never
gets freed, and memory consumption is much more easily noticed.
Publication date: Sat, 16 Mar 2024 02:15:00 +0000