Linux内核v4.4.52移植v4.11的SipHash补丁替换MD5的可行性、方法及报错求助

Hey there! Let's break this down clearly—yes, it’s absolutely feasible to backport the SipHash patch from kernel v4.11 to v4.4.52 to replace MD5 for enhanced security, but you can’t just slap the patch on directly. The v4.4 LTS branch has structural and code differences from v4.11, so you’ll need to manually adapt the changes. Here’s a step-by-step guide to do it right, plus fixes for common errors:

1. First: Confirm Feasibility #

The core goal—replacing MD5 with SipHash in specific kernel paths (like proc PID hashing and sysctl configuration, per the commit you referenced)—is totally achievable. The catch is that v4.4.52 doesn’t have built-in, complete SipHash support, so you’ll need to port that foundational code first before applying the MD5 replacement logic.

2. Proper Backporting Steps #

Step 1: Prep Your Kernel Source #

Start with a clean v4.4.52 source tree and make a backup to avoid messing up your work:

git clone https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
cd linux
git checkout v4.4.52
cp -r . ../linux-4.4.52-backup  # Safe backup

Step 2: Analyze the Target Commit #

The commit you’re targeting modifies key files like fs/proc/base.c, include/linux/hash.h, and kernel/sysctl.c to swap MD5 with SipHash. First, pull up the commit’s changes and note exactly what it does:

• Replaces MD5-based hash generation for proc entries with SipHash
• Adds SipHash configuration via sysctl
• Updates hash function prototypes

Step 3: Port SipHash Core to v4.4.52 #

v4.4.52 doesn’t include SipHash by default, so you need to add its core implementation first:

• Grab lib/siphash.c and include/linux/siphash.h from the v4.11 kernel source
• Copy these files to the corresponding directories in your v4.4.52 tree
• Modify lib/Kconfig to add a config option for SipHash:

  config SIPHASH
          bool "SipHash algorithm support"
          default y
          help
            Enable SipHash, a fast cryptographic hash function designed for
            use in hash tables and other situations where a secure hash
            is needed.
  

• Update lib/Makefile to include SipHash when the config is enabled:

  obj-$(CONFIG_SIPHASH) += siphash.o
  

Step 4: Manually Apply the MD5 Replacement Changes #

Don’t use git apply directly—instead, manually replicate the commit’s changes in v4.4.52’s files, adjusting for version differences:

• In fs/proc/base.c: Locate the MD5-based proc_pid_hash function and replace it with the SipHash equivalent. Note that function signatures or variable names might differ in v4.4, so tweak the code to match the existing context.
• In kernel/sysctl.c: Add the SipHash sysctl configuration entries, making sure they fit v4.4’s sysctl structure (the way sysctl nodes are defined might have changed since v4.11).
• In include/linux/hash.h: Update the hash function prototypes to use SipHash instead of MD5 where needed.

Step 5: Compile and Test #

Configure your kernel (keep your existing config and ensure SipHash is enabled):

make oldconfig
# When prompted, enable CONFIG_SIPHASH if it’s not already set
make -j$(nproc)

Test the new kernel in a safe environment (like QEMU) first, verifying that:

• Proc filesystem functionality works as expected
• Sysctl entries for SipHash are accessible and functional
• No crashes or performance regressions occur

3. Fixing Common Patch Application Errors #

If you tried applying the patch directly and got errors, here’s why and how to fix them:

• File conflicts: v4.4’s file structure differs from v4.11. Use git apply --reject to generate .rej files showing conflicting sections, then manually edit those parts to match v4.4’s code.
• Undefined SipHash functions: This happens because v4.4 doesn’t have SipHash built-in. Follow Step 3 above to port the core SipHash code first.
• Sysctl configuration mismatches: v4.4’s sysctl node hierarchy might be different. Adjust the patch’s sysctl changes to fit v4.4’s existing sysctl setup.

4. Extra Tips for Stability #

• Test thoroughly: Replacing a core hash function can affect unexpected parts of the kernel. Test proc access, sysctl settings, and any other features that rely on the original MD5 implementation.
• Keep track of changes: Use git to commit your porting steps incrementally, so you can roll back if something breaks.
• Check for existing backports: Some Linux distributions might already have backported this change to their v4.4 LTS kernels—you can reference their patches to save time.

备注：内容来源于stack exchange，提问作者Nikita