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| author | Daniel Borkmann <daniel@iogearbox.net> | 2026-04-16 15:27:19 +0300 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2026-04-16 17:35:22 +0300 |
| commit | e5f635edd393aeaa7cad9e42831d397e6e2e1eed (patch) | |
| tree | 14bbc781a366d1213e5b1ace1b4e609863e0c7f5 | |
| parent | 1cedfe17badeebdcc044855713597ac7db58414a (diff) | |
| download | linux-e5f635edd393aeaa7cad9e42831d397e6e2e1eed.tar.xz | |
bpf: Fix precedence bug in convert_bpf_ld_abs alignment check
Fix an operator precedence issue in convert_bpf_ld_abs() where the
expression offset + ip_align % size evaluates as offset + (ip_align % size)
due to % having higher precedence than +. That latter evaluation does
not make any sense. The intended check is (offset + ip_align) % size == 0
to verify that the packet load offset is properly aligned for direct
access.
With NET_IP_ALIGN == 2, the bug causes the inline fast-path for direct
packet loads to almost never be taken on !CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
platforms. This forces nearly all cBPF BPF_LD_ABS packet loads through
the bpf_skb_load_helper slow path on the affected archs.
Fixes: e0cea7ce988c ("bpf: implement ld_abs/ld_ind in native bpf")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20260416122719.661033-1-daniel@iogearbox.net
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
| -rw-r--r-- | net/core/filter.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/net/core/filter.c b/net/core/filter.c index fcfcb72663ca..5fa9189eb772 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -503,7 +503,7 @@ static bool convert_bpf_ld_abs(struct sock_filter *fp, struct bpf_insn **insnp) ((unaligned_ok && offset >= 0) || (!unaligned_ok && offset >= 0 && offset + ip_align >= 0 && - offset + ip_align % size == 0))) { + (offset + ip_align) % size == 0))) { bool ldx_off_ok = offset <= S16_MAX; *insn++ = BPF_MOV64_REG(BPF_REG_TMP, BPF_REG_H); |