libbpf-tools: fix stack smashing in ksyms__load from long kernel symbol names

[Copilot]

Rust-mangled kernel symbols can exceed 287 characters. ksyms__load used a 256-byte stack buffer with an unbounded %s in fscanf, causing a stack buffer overflow and SIGABRT in tools that load ksyms (biosnoop, biotop, biostacks, etc.).

Changes

• libbpf-tools/trace_helpers.c
  • Increase sym_name buffer: char sym_name[256] → char sym_name[2048]
  • Add matching width guard in fscanf: %s → %2047s

// Before
char sym_type, sym_name[256];
...
ret = fscanf(f, "%lx %c %s%*[^\n]\n", &sym_addr, &sym_type, sym_name);

// After
char sym_type, sym_name[2048];
...
ret = fscanf(f, "%lx %c %2047s%*[^\n]\n", &sym_addr, &sym_type, sym_name);

The 2048-byte buffer provides headroom well beyond current observed maximums; the %2047s width specifier enforces a hard bound regardless of future symbol length growth.

Original prompt

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This section details on the original issue you should resolve

<issue_title>biosnoop fails w/ stack smashing detected</issue_title>
<issue_description>### Environment

• OS: Arch Linux
• Package version: bcc-libbpf-tools=0.36.1-1
• Kernel: "vanilla" kernel. Version 6.18.9.arch1-2

Steps to reproduce

• Run sudo biosnoop. Also reproducible with biotop and biostacks (maybe more)

Expected Behavior

Works as usual

Actual Behavior

Exits with the following error message:

*** stack smashing detected ***: terminated
fish: Job 1, 'sudo biotop' terminated by signal SIGABRT (Abort)

Exit code is 134.

Possible Root Cause

Diagnosed by @heftig:

wc -L /proc/kallsyms reports 306 /proc/kallsyms for linux-zen. There's at least one symbol with a very long name, up to 287 characters. It's probably one of the mangled symbols of Rust code.

The ksyms__load function uses an on-stack string (char sym_name[256]) to hold the name of each symbol it reads, and reading any name longer than 255 characters causes a buffer overflow.

Misc

• Downstream issue: https://gitlab.archlinux.org/archlinux/packaging/packages/bcc/-/issues/6

Comments on the Issue (you are @copilot in this section)

• Fixes biosnoop fails w/ stack smashing detected #5468

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