bpf: Reject rdonly/rdwr_buf_size kfunc arguments that exceed u32 max

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check_kfunc_args() detects a kfunc argument named rdonly_buf_size or
rdwr_buf_size and stores reg->var_off.value into meta->r0_size, a u64,
and does not bound it. check_kfunc_call() later copies that value into
the returned register's mem_size field:

  meta->r0_size = reg->var_off.value;
  ...
  regs[BPF_REG_0].mem_size = meta.r0_size;

regs[BPF_REG_0].mem_size is u32. A constant whose upper 32 bits are set
gets truncated instead of causing a load-time rejection, so the verifier
records a PTR_TO_MEM register with an approximately 4 GiB mem_size for
whatever allocation the kfunc returned. A later access check against
that register uses the truncated, wrong bound.

Reject rdonly_buf_size/rdwr_buf_size values that exceed U32_MAX at the
point meta->r0_size is set.

Fixes: eb1f7f71c1 ("bpf/verifier: allow kfunc to return an allocated mem")
Signed-off-by: Nicholas Dudar <main.kalliope@gmail.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20260709155837.1879230-2-main.kalliope@gmail.com
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

...

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Nicholas Dudar 2026-07-09 11:58:36 -04:00 • committed by Kumar Kartikeya Dwivedi

parent c3d5ef291a

commit 2aaf67f051

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kernel/bpf/verifier.c

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