Loop with Unreachable Exit Condition ('Infinite Loop') Affecting kernel package, versions *

Note: Versions mentioned in the description apply only to the upstream kernel package and not the kernel package as distributed by Centos. See How to fix? for Centos:7 relevant fixed versions and status.

In the Linux kernel, the following vulnerability has been resolved:

libfs: fix infinite directory reads for offset dir

After we switch tmpfs dir operations from simple_dir_operations to simple_offset_dir_operations, every rename happened will fill new dentry to dest dir's maple tree(&SHMEM_I(inode)->dir_offsets->mt) with a free key starting with octx->newx_offset, and then set newx_offset equals to free key + 1. This will lead to infinite readdir combine with rename happened at the same time, which fail generic/736 in xfstests(detail show as below).

1. create 5000 files(1 2 3...) under one dir
2. call readdir(man 3 readdir) once, and get one entry
3. rename(entry, "TEMPFILE"), then rename("TEMPFILE", entry)
4. loop 2~3, until readdir return nothing or we loop too many times(tmpfs break test with the second condition)

We choose the same logic what commit 9b378f6ad48cf ("btrfs: fix infinite directory reads") to fix it, record the last_index when we open dir, and do not emit the entry which index >= last_index. The file->private_data now used in offset dir can use directly to do this, and we also update the last_index when we llseek the dir file.

[brauner: only update last_index after seek when offset is zero like Jan suggested]

• https://access.redhat.com/security/cve/CVE-2024-46701
• https://git.kernel.org/stable/c/308b4fc2403b335894592ee9dc212a5e58bb309f
• https://git.kernel.org/stable/c/64a7ce76fb901bf9f9c36cf5d681328fc0fd4b5a