diff options
| author | Daniel Borkmann <daniel@iogearbox.net> | 2026-04-09 17:50:15 +0200 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2026-04-09 13:11:31 -0700 |
| commit | 9f118095dd341885dbc3f1cd6a028414da099aba (patch) | |
| tree | 6afecdbc7c616ad74ac623771cb2421796b07a46 /kernel | |
| parent | e0fcb42bc6f41bab2895757d6610616b3820eff7 (diff) | |
bpf: Drop pkt_end markers on arithmetic to prevent is_pkt_ptr_branch_taken
When a pkt pointer acquires AT_PKT_END or BEYOND_PKT_END range from
a comparison, and then, known-constant arithmetic is performed,
adjust_ptr_min_max_vals() copies the stale range via dst_reg->raw =
ptr_reg->raw without clearing the negative reg->range sentinel values.
This lets is_pkt_ptr_branch_taken() choose one branch direction and
skip going through the other. Fix this by clearing negative pkt range
values (that is, AT_PKT_END and BEYOND_PKT_END) after arithmetic on
pkt pointers. This ensures is_pkt_ptr_branch_taken() returns unknown
and both branches are properly verified.
Fixes: 6d94e741a8ff ("bpf: Support for pointers beyond pkt_end.")
Reported-by: STAR Labs SG <info@starlabs.sg>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20260409155016.536608-1-daniel@iogearbox.net
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/bpf/verifier.c | 30 |
1 files changed, 22 insertions, 8 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 1227b168bb07..9c1135d373e2 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -15448,10 +15448,17 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, } dst_reg->var_off = tnum_add(ptr_reg->var_off, off_reg->var_off); dst_reg->raw = ptr_reg->raw; - if (!known && reg_is_pkt_pointer(ptr_reg)) { - dst_reg->id = ++env->id_gen; - /* something was added to pkt_ptr, set range to zero */ - memset(&dst_reg->raw, 0, sizeof(dst_reg->raw)); + if (reg_is_pkt_pointer(ptr_reg)) { + if (!known) + dst_reg->id = ++env->id_gen; + /* + * Clear range for unknown addends since we can't know + * where the pkt pointer ended up. Also clear AT_PKT_END / + * BEYOND_PKT_END from prior comparison as any pointer + * arithmetic invalidates them. + */ + if (!known || dst_reg->range < 0) + memset(&dst_reg->raw, 0, sizeof(dst_reg->raw)); } break; case BPF_SUB: @@ -15490,10 +15497,17 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, } dst_reg->var_off = tnum_sub(ptr_reg->var_off, off_reg->var_off); dst_reg->raw = ptr_reg->raw; - if (!known && reg_is_pkt_pointer(ptr_reg)) { - dst_reg->id = ++env->id_gen; - /* something was added to pkt_ptr, set range to zero */ - if (smin_val < 0) + if (reg_is_pkt_pointer(ptr_reg)) { + if (!known) + dst_reg->id = ++env->id_gen; + /* + * Clear range if the subtrahend may be negative since + * pkt pointer could move past its bounds. A positive + * subtrahend moves it backwards keeping positive range + * intact. Also clear AT_PKT_END / BEYOND_PKT_END from + * prior comparison as arithmetic invalidates them. + */ + if ((!known && smin_val < 0) || dst_reg->range < 0) memset(&dst_reg->raw, 0, sizeof(dst_reg->raw)); } break; |