[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20251001192859.2343567-2-listout@listout.xyz>
Date: Thu, 2 Oct 2025 00:58:58 +0530
From: Brahmajit Das <listout@...tout.xyz>
To: syzbot+d36d5ae81e1b0a53ef58@...kaller.appspotmail.com
Cc: andrii@...nel.org,
ast@...nel.org,
bpf@...r.kernel.org,
daniel@...earbox.net,
eddyz87@...il.com,
haoluo@...gle.com,
john.fastabend@...il.com,
jolsa@...nel.org,
kpsingh@...nel.org,
linux-kernel@...r.kernel.org,
martin.lau@...ux.dev,
sdf@...ichev.me,
song@...nel.org,
syzkaller-bugs@...glegroups.com,
yonghong.song@...ux.dev,
KaFai Wan <kafai.wan@...ux.dev>
Subject: [PATCH v4 1/2] bpf: Skip scalar adjustment for BPF_NEG if dst is a pointer
In check_alu_op(), the verifier currently calls check_reg_arg() and
adjust_scalar_min_max_vals() unconditionally for BPF_NEG operations.
However, if the destination register holds a pointer, these scalar
adjustments are unnecessary and potentially incorrect.
This patch adds a check to skip the adjustment logic when the destination
register contains a pointer.
Reported-by: syzbot+d36d5ae81e1b0a53ef58@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=d36d5ae81e1b0a53ef58
Fixes: aced132599b3 ("bpf: Add range tracking for BPF_NEG")
Suggested-by: KaFai Wan <kafai.wan@...ux.dev>
Suggested-by: Eduard Zingerman <eddyz87@...il.com>
Signed-off-by: Brahmajit Das <listout@...tout.xyz>
---
Changes v4:
Cleaning up, instead of using __is_pointer_value it's further
simplified by checking if regs[insn->dst_reg].type of SCALAR_VALUE
Link:
Changes in v3:
using __is_pointer_value to check if register if of pointer type
Link: https://lore.kernel.org/all/20251001095613.267475-1-listout@listout.xyz/
Changes in v2:
Checking if reg->map_ptr is NULL in bpf/log.c but with cleaner approach
(wrong approach)
Link: https://lore.kernel.org/all/20250923174738.1713751-1-listout@listout.xyz/
Changes in v1:
Checking if reg->map_ptr is NULL in bpf/log.c (wrong approach)
Link: https://lore.kernel.org/all/20250923164144.1573636-1-listout@listout.xyz/
---
kernel/bpf/verifier.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e892df386eed..f3d8ba142faa 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -15645,7 +15645,8 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
}
/* check dest operand */
- if (opcode == BPF_NEG) {
+ if (opcode == BPF_NEG &&
+ regs[insn->dst_reg].type == SCALAR_VALUE) {
err = check_reg_arg(env, insn->dst_reg, DST_OP_NO_MARK);
err = err ?: adjust_scalar_min_max_vals(env, insn,
®s[insn->dst_reg],
--
2.51.0
Powered by blists - more mailing lists