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Kumar Kartikeya Dwivedi d8edc163cc bpf: Fix sleepable context for async callbacks 
[ Upstream commit 469d638d15 ]

Fix the BPF verifier to correctly determine the sleepable context of
async callbacks based on the async primitive type rather than the arming
program's context.

The bug is in in_sleepable() which uses OR logic to check if the current
execution context is sleepable. When a sleepable program arms a timer
callback, the callback's state correctly has in_sleepable=false, but
in_sleepable() would still return true due to env->prog->sleepable being
true. This incorrectly allows sleepable helpers like
bpf_copy_from_user() inside timer callbacks when armed from sleepable
programs, even though timer callbacks always execute in non-sleepable
context.

Fix in_sleepable() to rely solely on env->cur_state->in_sleepable, and
initialize state->in_sleepable to env->prog->sleepable in
do_check_common() for the main program entry. This ensures the sleepable
context is properly tracked per verification state rather than being
overridden by the program's sleepability.

The env->cur_state NULL check in in_sleepable() was only needed for
do_misc_fixups() which runs after verification when env->cur_state is
set to NULL. Update do_misc_fixups() to use env->prog->sleepable
directly for the storage_get_function check, and remove the redundant
NULL check from in_sleepable().

Introduce is_async_cb_sleepable() helper to explicitly determine async
callback sleepability based on the primitive type:
  - bpf_timer callbacks are never sleepable
  - bpf_wq and bpf_task_work callbacks are always sleepable

Add verifier_bug() check to catch unhandled async callback types,
ensuring future additions cannot be silently mishandled. Move the
is_task_work_add_kfunc() forward declaration to the top alongside other
callback-related helpers. We update push_async_cb() to adjust to the new
changes.

At the same time, while simplifying in_sleepable(), we notice a problem
in do_misc_fixups. Fix storage_get helpers to use GFP_ATOMIC when called
from non-sleepable contexts within sleepable programs, such as bpf_timer
callbacks.

Currently, the check in do_misc_fixups assumes that env->prog->sleepable,
previously in_sleepable(env) which only resolved to this check before
last commit, holds across the program's execution, but that is not true.
Instead, the func_atomic bit must be set whenever we see the function
being called in an atomic context. Previously, this is being done when
the helper is invoked in atomic contexts in sleepable programs, we can
simply just set the value to true without doing an in_sleepable() check.

We must also do a standalone in_sleepable() check to handle cases where
the async callback itself is armed from a sleepable program, but is
itself non-sleepable (e.g., timer callback) and invokes such a helper,
thus needing the func_atomic bit to be true for the said call.

Adjust do_misc_fixups() to drop any checks regarding sleepable nature of
the program, and just depend on the func_atomic bit to decide which GFP
flag to pass.

Fixes: 81f1d7a583 ("bpf: wq: add bpf_wq_set_callback_impl")
Fixes: b00fa38a9c ("bpf: Enable non-atomic allocations in local storage")
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20251007220349.3852807-2-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-12-18 14:02:26 +01:00
arch KVM: SVM: Don't skip unrelated instruction if INT3/INTO is replaced 2025-12-12 18:42:45 +01:00
block vfs-6.18-rc7.fixes 2025-11-17 09:11:27 -08:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: zstd - fix double-free in per-CPU stream cleanup 2025-12-12 18:42:45 +01:00
Documentation smack: fix bug: setting task label silently ignores input garbage 2025-12-18 14:02:25 +01:00
drivers drm/vgem-fence: Fix potential deadlock on release 2025-12-18 14:02:26 +01:00
fs ext4: add i_data_sem protection in ext4_destroy_inline_data_nolock() 2025-12-12 18:42:45 +01:00
include Char/Misc/IIO fixes for 6.18-rc8 2025-11-28 09:44:48 -08:00
init printk changes for 6.18 2025-10-04 11:13:11 -07:00
io_uring io_uring: fix mixed cqe overflow handling 2025-11-25 07:03:45 -07:00
ipc namespace-6.18-rc1 2025-09-29 11:20:29 -07:00
kernel bpf: Fix sleepable context for async callbacks 2025-12-18 14:02:26 +01:00
lib Increase the default 32-bit build frame size warning limit to 1280 bytes 2025-11-26 12:11:28 -08:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm 8 hotfixes. 4 are cc:stable, 7 are against mm/. 2025-11-26 12:38:05 -08:00
net A patch to make sparse read handling work in msgr2 secure mode from 2025-11-27 11:11:03 -08:00
rust rust: Add -fno-isolate-erroneous-paths-dereference to bindgen_skip_c_flags 2025-11-10 08:37:06 +08:00
samples samples: work around glibc redefining some of our defines wrong 2025-11-21 09:29:02 -08:00
scripts Rust fixes for v6.18 (2nd) 2025-11-14 15:36:15 -08:00
security smack: fix bug: setting task label silently ignores input garbage 2025-12-18 14:02:25 +01:00
sound ALSA: hda/realtek: Add quirk for HP ProBook 450 G8 2025-11-26 07:26:56 +01:00
tools 8 hotfixes. 4 are cc:stable, 7 are against mm/. 2025-11-26 12:38:05 -08:00
usr gen_init_cpio: Ignore fsync() returning EINVAL on pipes 2025-10-07 09:53:05 -07:00
virt KVM: guest_memfd: Remove bindings on memslot deletion when gmem is dying 2025-11-04 09:16:53 -08:00
.clang-format memblock: drop for_each_free_mem_pfn_range_in_zone_from() 2025-09-14 08:49:03 +03:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore compile_commands.json globally 2025-08-12 15:53:55 -07:00
.mailmap 8 hotfixes. 4 are cc:stable, 7 are against mm/. 2025-11-26 12:38:05 -08:00
.pylintrc tools: docs: parse-headers.py: move it from sphinx dir 2025-08-29 15:54:42 -06:00
.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: mark ISDN subsystem as orphan 2025-10-27 17:49:45 -07:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS soc: fixes for 6.18, part 4 2025-11-28 09:57:31 -08:00
Makefile Linux 6.18.1 2025-12-12 18:42:47 +01:00
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.