diff options
| author | Shung-Hsi Yu | 2022-10-12 10:23:51 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman | 2022-12-31 13:32:02 +0100 |
| commit | 622ff59742fe7bf53c06a57332040fa0e08b8242 (patch) | |
| tree | ba74f4b83329198725f19b49df432cc8c004b0f8 | |
| parent | 3c48bbf4264f4575c87d41d8a96f8502b598e626 (diff) | |
libbpf: Use elf_getshdrnum() instead of e_shnum
[ Upstream commit 51deedc9b8680953437dfe359e5268120de10e30 ]
This commit replace e_shnum with the elf_getshdrnum() helper to fix two
oss-fuzz-reported heap-buffer overflow in __bpf_object__open. Both
reports are incorrectly marked as fixed and while still being
reproducible in the latest libbpf.
# clusterfuzz-testcase-minimized-bpf-object-fuzzer-5747922482888704
libbpf: loading object 'fuzz-object' from buffer
libbpf: sec_cnt is 0
libbpf: elf: section(1) .data, size 0, link 538976288, flags 2020202020202020, type=2
libbpf: elf: section(2) .data, size 32, link 538976288, flags 202020202020ff20, type=1
=================================================================
==13==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x6020000000c0 at pc 0x0000005a7b46 bp 0x7ffd12214af0 sp 0x7ffd12214ae8
WRITE of size 4 at 0x6020000000c0 thread T0
SCARINESS: 46 (4-byte-write-heap-buffer-overflow-far-from-bounds)
#0 0x5a7b45 in bpf_object__elf_collect /src/libbpf/src/libbpf.c:3414:24
#1 0x5733c0 in bpf_object_open /src/libbpf/src/libbpf.c:7223:16
#2 0x5739fd in bpf_object__open_mem /src/libbpf/src/libbpf.c:7263:20
...
The issue lie in libbpf's direct use of e_shnum field in ELF header as
the section header count. Where as libelf implemented an extra logic
that, when e_shnum == 0 && e_shoff != 0, will use sh_size member of the
initial section header as the real section header count (part of ELF
spec to accommodate situation where section header counter is larger
than SHN_LORESERVE).
The above inconsistency lead to libbpf writing into a zero-entry calloc
area. So intead of using e_shnum directly, use the elf_getshdrnum()
helper provided by libelf to retrieve the section header counter into
sec_cnt.
Fixes: 0d6988e16a12 ("libbpf: Fix section counting logic")
Fixes: 25bbbd7a444b ("libbpf: Remove assumptions about uniqueness of .rodata/.data/.bss maps")
Signed-off-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=40868
Link: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=40957
Link: https://lore.kernel.org/bpf/20221012022353.7350-2-shung-hsi.yu@suse.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
| -rw-r--r-- | tools/lib/bpf/libbpf.c | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 91b7106a4a73..b7fac0df2612 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -597,7 +597,7 @@ struct elf_state { size_t shstrndx; /* section index for section name strings */ size_t strtabidx; struct elf_sec_desc *secs; - int sec_cnt; + size_t sec_cnt; int btf_maps_shndx; __u32 btf_maps_sec_btf_id; int text_shndx; @@ -3312,10 +3312,15 @@ static int bpf_object__elf_collect(struct bpf_object *obj) Elf64_Shdr *sh; /* ELF section indices are 0-based, but sec #0 is special "invalid" - * section. e_shnum does include sec #0, so e_shnum is the necessary - * size of an array to keep all the sections. + * section. Since section count retrieved by elf_getshdrnum() does + * include sec #0, it is already the necessary size of an array to keep + * all the sections. */ - obj->efile.sec_cnt = obj->efile.ehdr->e_shnum; + if (elf_getshdrnum(obj->efile.elf, &obj->efile.sec_cnt)) { + pr_warn("elf: failed to get the number of sections for %s: %s\n", + obj->path, elf_errmsg(-1)); + return -LIBBPF_ERRNO__FORMAT; + } obj->efile.secs = calloc(obj->efile.sec_cnt, sizeof(*obj->efile.secs)); if (!obj->efile.secs) return -ENOMEM; |