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ee684de5c1
As shown in [1], it is possible to corrupt a BPF ELF file such that
arbitrary BPF instructions are loaded by libbpf. This can be done by
setting a symbol (BPF program) section offset to a large (unsigned)
number such that <section start + symbol offset> overflows and points
before the section data in the memory.
Consider the situation below where:
- prog_start = sec_start + symbol_offset <-- size_t overflow here
- prog_end = prog_start + prog_size
prog_start sec_start prog_end sec_end
| | | |
v v v v
.....................|################################|............
The report in [1] also provides a corrupted BPF ELF which can be used as
a reproducer:
$ readelf -S crash
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
...
[ 2] uretprobe.mu[...] PROGBITS 0000000000000000 00000040
0000000000000068 0000000000000000 AX 0 0 8
$ readelf -s crash
Symbol table '.symtab' contains 8 entries:
Num: Value Size Type Bind Vis Ndx Name
...
6: ffffffffffffffb8 104 FUNC GLOBAL DEFAULT 2 handle_tp
Here, the handle_tp prog has section offset ffffffffffffffb8, i.e. will
point before the actual memory where section 2 is allocated.
This is also reported by AddressSanitizer:
=================================================================
==1232==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x7c7302fe0000 at pc 0x7fc3046e4b77 bp 0x7ffe64677cd0 sp 0x7ffe64677490
READ of size 104 at 0x7c7302fe0000 thread T0
#0 0x7fc3046e4b76 in memcpy (/lib64/libasan.so.8+0xe4b76)
#1 0x00000040df3e in bpf_object__init_prog /src/libbpf/src/libbpf.c:856
#2 0x00000040df3e in bpf_object__add_programs /src/libbpf/src/libbpf.c:928
#3 0x00000040df3e in bpf_object__elf_collect /src/libbpf/src/libbpf.c:3930
#4 0x00000040df3e in bpf_object_open /src/libbpf/src/libbpf.c:8067
#5 0x00000040f176 in bpf_object__open_file /src/libbpf/src/libbpf.c:8090
#6 0x000000400c16 in main /poc/poc.c:8
#7 0x7fc3043d25b4 in __libc_start_call_main (/lib64/libc.so.6+0x35b4)
#8 0x7fc3043d2667 in __libc_start_main@@GLIBC_2.34 (/lib64/libc.so.6+0x3667)
#9 0x000000400b34 in _start (/poc/poc+0x400b34)
0x7c7302fe0000 is located 64 bytes before 104-byte region [0x7c7302fe0040,0x7c7302fe00a8)
allocated by thread T0 here:
#0 0x7fc3046e716b in malloc (/lib64/libasan.so.8+0xe716b)
#1 0x7fc3045ee600 in __libelf_set_rawdata_wrlock (/lib64/libelf.so.1+0xb600)
#2 0x7fc3045ef018 in __elf_getdata_rdlock (/lib64/libelf.so.1+0xc018)
#3 0x00000040642f in elf_sec_data /src/libbpf/src/libbpf.c:3740
The problem here is that currently, libbpf only checks that the program
end is within the section bounds. There used to be a check
`while (sec_off < sec_sz)` in bpf_object__add_programs, however, it was
removed by commit
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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.