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Kumar Kartikeya Dwivedi 7aa5a19279 bpf: Defer work in bpf_timer_cancel_and_free 
[ Upstream commit a6fcd19d7e ]

Currently, the same case as previous patch (two timer callbacks trying
to cancel each other) can be invoked through bpf_map_update_elem as
well, or more precisely, freeing map elements containing timers. Since
this relies on hrtimer_cancel as well, it is prone to the same deadlock
situation as the previous patch.

It would be sufficient to use hrtimer_try_to_cancel to fix this problem,
as the timer cannot be enqueued after async_cancel_and_free. Once
async_cancel_and_free has been done, the timer must be reinitialized
before it can be armed again. The callback running in parallel trying to
arm the timer will fail, and freeing bpf_hrtimer without waiting is
sufficient (given kfree_rcu), and bpf_timer_cb will return
HRTIMER_NORESTART, preventing the timer from being rearmed again.

However, there exists a UAF scenario where the callback arms the timer
before entering this function, such that if cancellation fails (due to
timer callback invoking this routine, or the target timer callback
running concurrently). In such a case, if the timer expiration is
significantly far in the future, the RCU grace period expiration
happening before it will free the bpf_hrtimer state and along with it
the struct hrtimer, that is enqueued.

Hence, it is clear cancellation needs to occur after
async_cancel_and_free, and yet it cannot be done inline due to deadlock
issues. We thus modify bpf_timer_cancel_and_free to defer work to the
global workqueue, adding a work_struct alongside rcu_head (both used at
_different_ points of time, so can share space).

Update existing code comments to reflect the new state of affairs.

Fixes: b00628b1c7 ("bpf: Introduce bpf timers.")
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20240709185440.1104957-3-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2024-07-18 13:22:40 +02:00
arch arm64: dts: rockchip: Fix the DCDC_REG2 minimum voltage on Quartz64 Model B 2024-07-11 12:51:20 +02:00
block block: check for max_hw_sectors underflow 2024-07-11 12:51:22 +02:00
certs This update includes the following changes: 2023-11-02 16:15:30 -10:00
crypto crypto: aead,cipher - zeroize key buffer after use 2024-07-11 12:50:58 +02:00
Documentation kbuild: doc: Update default INSTALL_MOD_DIR from extra to updates 2024-07-05 09:38:06 +02:00
drivers net: ethernet: lantiq_etop: fix double free in detach 2024-07-18 13:22:39 +02:00
fs minixfs: Fix minixfs_rename with HIGHMEM 2024-07-18 13:22:39 +02:00
include spi: add defer_optimize_message controller flag 2024-07-18 13:22:38 +02:00
init printk: Fix LOG_CPU_MAX_BUF_SHIFT when BASE_SMALL is enabled 2024-06-12 11:39:35 +02:00
io_uring io_uring: signal SQPOLL task_work with TWA_SIGNAL_NO_IPI 2024-07-05 09:38:15 +02:00
ipc sysctl changes for v6.9-rc1 2024-03-18 14:59:13 -07:00
kernel bpf: Defer work in bpf_timer_cancel_and_free 2024-07-18 13:22:40 +02:00
lib kunit: Fix timeout message 2024-07-11 12:51:04 +02:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm Revert "mm/writeback: fix possible divide-by-zero in wb_dirty_limits(), again" 2024-07-11 12:51:17 +02:00
net net: fix rc7's __skb_datagram_iter() 2024-07-18 13:22:39 +02:00
rust rust: remove params from module macro example 2024-04-25 17:34:33 +02:00
samples samples/landlock: Fix incorrect free in populate_ruleset_net 2024-05-30 09:45:01 +02:00
scripts kbuild: fix short log for AS in link-vmlinux.sh 2024-07-11 12:51:23 +02:00
security evm: Enforce signatures on unsupported filesystem for EVM_INIT_X509 2024-07-05 09:38:00 +02:00
sound ALSA: ump: Set default protocol when not given explicitly 2024-07-11 12:51:23 +02:00
tools libbpf: don't close(-1) in multi-uprobe feature detector 2024-07-11 12:51:24 +02:00
usr Kbuild updates for v6.8 2024-01-18 17:57:07 -08:00
virt virt: guest_memfd: fix reference leak on hwpoisoned page 2024-06-27 13:52:31 +02:00
.clang-format clang-format: Update with v6.7-rc4's for_each macro list 2023-12-08 23:54:38 +01:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-21 14:40:11 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: create a list of all built DTB files 2024-02-19 18:20:39 +09:00
.mailmap 18 hotfixes, 7 of which are cc:stable. 2024-05-10 14:16:03 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Drop Gustavo Pimentel as PCI DWC Maintainer 2024-03-27 13:41:02 -05:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS cpufreq: amd-pstate: remove global header file 2024-06-21 14:40:00 +02:00
Makefile Linux 6.9.9 2024-07-11 12:51:24 +02:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

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.