CVE-2023-52699

In the Linux kernel, the following vulnerability has been resolved: sysv:
don’t call sb_bread() with pointers_lock held syzbot is reporting sleep in
atomic context in SysV filesystem [1], for sb_bread() is called with
rw_spinlock held. A “write_lock(&pointers_lock) =>
read_lock(&pointers_lock) deadlock” bug and a “sb_bread() with
write_lock(&pointers_lock)” bug were introduced by “Replace BKL for chain
locking with sysvfs-private rwlock” in Linux 2.5.12. Then, “[PATCH]
err1-40: sysvfs locking fix” in Linux 2.6.8 fixed the former bug by moving
pointers_lock lock to the callers, but instead introduced a “sb_bread()
with read_lock(&pointers_lock)” bug (which made this problem easier to
hit). Al Viro suggested that why not to do like get_branch()/get_block()/
find_shared() in Minix filesystem does. And doing like that is almost a
revert of “[PATCH] err1-40: sysvfs locking fix” except that get_branch()
from with find_shared() is called without write_lock(&pointers_lock).