bpf: potential double-free of env->insn_aux_data

Function bpf_patch_insn_data() has the following structure:

  static struct bpf_prog *bpf_patch_insn_data(... env ...)
  {
        struct bpf_prog *new_prog;
        struct bpf_insn_aux_data *new_data = NULL;

        if (len > 1) {
                new_data = vrealloc(...);  // <--------- (1)
                if (!new_data)
                        return NULL;

                env->insn_aux_data = new_data;  // <---- (2)
        }

        new_prog = bpf_patch_insn_single(env->prog, off, patch, len);
        if (IS_ERR(new_prog)) {
                ...
                vfree(new_data);   // <----------------- (3)
                return NULL;
        }
        ... happy path ...
  }

In case if bpf_patch_insn_single() returns an error the `new_data`
allocated at (1) will be freed at (3). However, at (2) this pointer
is stored in `env->insn_aux_data`. Which is freed unconditionally
by verifier.c:bpf_check() on both happy and error paths.
Thus, leading to double-free.

Fix this by removing vfree() call at (3), ownership over `new_data` is
already passed to `env->insn_aux_data` at this point.

Fixes: 77620d126739 ("bpf: use realloc in bpf_patch_insn_data")
Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20250912-patch-insn-data-double-free-v1-1-af05bd85a21a@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 17fe623400a5bcd7faf900c92e54994be952c628..1029380f84db3e9a3033aed18dcb4fa62da1467e 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -20800,7 +20800,6 @@ static struct bpf_prog *bpf_patch_insn_data(struct bpf_verifier_env *env, u32 of
                        verbose(env,
                                "insn %d cannot be patched due to 16-bit range\n",
                                env->insn_aux_data[off].orig_idx);
-               vfree(new_data);
                return NULL;
        }
        adjust_insn_aux_data(env, new_prog, off, len);