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1970fc4ecb
bpf_binprm_set_interp() tests path[0] != '/' on the buffer its load
program passes and then reads the same buffer again to copy it with
kmemdup_nul(). The buffer can be a BPF map value that another CPU
rewrites between the two reads. If byte 0 is overwritten in that
window, the kfunc stages a relative or empty interpreter path. The
staged path is not checked again, so open_exec() resolves a relative
path against the working directory of the task doing the exec.
bpf_binprm_set_interp_arg() has the same pattern for its "!len" test
and can stage an empty argument, which the interpreter then receives
as an empty argv entry.
The verifier checks the path and path__sz pair with BPF_READ |
BPF_WRITE, so a writable array map value is an accepted argument.
bpf(BPF_MAP_UPDATE_ELEM) on an array map copies the new value over the
old one in place and takes no lock. Both kfuncs are KF_SLEEPABLE and
allocate with GFP_KERNEL between the test and the copy, so the task
can sleep inside the window:
load program bpf(BPF_MAP_UPDATE_ELEM)
bpf_binprm_set_interp()
strnlen(path, path__sz)
path[0] != '/' is false
kmemdup_nul(path, len, GFP_KERNEL)
allocation may sleep
array_map_update_elem()
copy_map_value()
rewrites byte 0
copy reads path again
bm_bpf_stage_selection()
The test in the load program's column proves what byte 0 held only at
the moment the test ran. The map update takes no lock, so it can store
to byte 0 right after. kmemdup_nul() then copies the rewritten bytes,
and bm_bpf_stage_selection() publishes them as bprm->bpf_interp.
The staged path is not checked again on its way to open_exec():
load_misc_binary()
entry_select_interpreter() returns bprm->bpf_interp unchanged
build_interp_argv()
copy_string_kernel() copies it as argv[0]
bprm_change_interp()
kstrdup()
entry_open_interpreter()
open_exec() unless a bound file is staged or
the entry is an 'F' entry
None of these functions tests the first byte, and load_misc_binary()
hands the pointer to nothing else.
In bpf_binprm_set_interp_arg(), strnlen() finds a non-zero len, a NUL
is then stored to byte 0, and build_interp_argv() later copies the
empty bprm->bpf_interp_arg with copy_string_kernel().
The handler's own load program has to pass a writable map value, and
something has to store into it while the kfunc runs. The allocation can
sleep inside the window, and with a BPF_F_MMAPABLE array the store is a
plain user space write into the mapped value, so a loop can hit it
without a single bpf() call.
Check the private copy in both kfuncs, so that the string that gets
staged is the string that was checked. bpf_binprm_select_interp()
already looks its name up in a private copy for the same reason. The
remaining tests work on path__sz, arg__sz or the local len, and the
copy length is len, so the copy stays inside the extent the verifier
checked.
Results of bpf_binprm_set_interp() with the check on the copy:
- A NUL stored to byte 0 fails interp[0] != '/' and gets -EINVAL.
- For len == 0, kmemdup_nul() returns an empty string, so an empty path
still gets -EINVAL.
- A NUL stored further into the string only shortens it to another
absolute path, or another non-empty argument, that the program could
have passed anyway.
- A path that both lacks the leading '/' and is PATH_MAX or longer now
gets -ENAMETOOLONG instead of -EINVAL.
- A path that is empty or lacks the leading '/' is now rejected after
the copy rather than before it, so such a call makes an allocation
and returns -ENOMEM instead of -EINVAL if that allocation fails.
bpf_binprm_set_interp_arg() still rejects an empty argument before
allocating, so its results are unchanged apart from the raced case
fixed here.
Both new checks run before the previously staged string is freed or
replaced. A failing call frees only its own allocation and leaves the
earlier selection in place, as the -ENOMEM path already does.
Fixes:
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer: Getting started with kernel development * Academic Researcher: Studying kernel internals and architecture * Security Expert: Hardening and vulnerability analysis * Backport/Maintenance Engineer: Maintaining stable kernels * System Administrator: Configuring and troubleshooting * Maintainer: Leading subsystems and reviewing patches * Hardware Vendor: Writing drivers for new hardware * Distribution Maintainer: Packaging kernels for distros * AI Coding Assistant: LLMs and AI-powered development tools For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. 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