[bpf-next 3/3] bpf: Fix a use after free in bpf_check()

From: He Fengqing
Date: Tue Jul 06 2021 - 23:53:08 EST

In bpf_patch_insn_data, env->prog was input parameter of
bpf_patch_insn_single function. bpf_patch_insn_single call
bpf_prog_realloc to realloc ebpf prog. When we need to malloc new prog,
bpf_prog_realloc will free the old prog, in this scenery is the
env->prog.
Then bpf_patch_insn_data function call adjust_insn_aux_data function, if
adjust_insn_aux_data function return error, bpf_patch_insn_data will
return NULL.
In bpf_check->convert_ctx_accesses->bpf_patch_insn_data call chain, if
bpf_patch_insn_data return NULL, env->prog has been freed in
bpf_prog_realloc, then bpf_check will use the freed env->prog.

Signed-off-by: He Fengqing <hefengqing@xxxxxxxxxx>
---
include/linux/filter.h | 2 +-
kernel/bpf/core.c | 9 ++++---
kernel/bpf/verifier.c | 53 ++++++++++++++++++++++++++++++++----------
net/core/filter.c | 2 +-
4 files changed, 49 insertions(+), 17 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index f39e008a377d..ec11a5ae92c2 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -881,7 +881,7 @@ void bpf_prog_jit_attempt_done(struct bpf_prog *prog);
struct bpf_prog *bpf_prog_alloc(unsigned int size, gfp_t gfp_extra_flags);
struct bpf_prog *bpf_prog_alloc_no_stats(unsigned int size, gfp_t gfp_extra_flags);
struct bpf_prog *bpf_prog_realloc(struct bpf_prog *fp_old, unsigned int size,
- gfp_t gfp_extra_flags);
+ gfp_t gfp_extra_flags, bool free_old);
void __bpf_prog_free(struct bpf_prog *fp);

static inline void bpf_prog_clone_free(struct bpf_prog *fp)
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 49b0311f48c1..e5616bb1665b 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -218,7 +218,7 @@ void bpf_prog_fill_jited_linfo(struct bpf_prog *prog,
}

struct bpf_prog *bpf_prog_realloc(struct bpf_prog *fp_old, unsigned int size,
- gfp_t gfp_extra_flags)
+ gfp_t gfp_extra_flags, bool free_old)
{
gfp_t gfp_flags = GFP_KERNEL_ACCOUNT | __GFP_ZERO | gfp_extra_flags;
struct bpf_prog *fp;
@@ -238,7 +238,8 @@ struct bpf_prog *bpf_prog_realloc(struct bpf_prog *fp_old, unsigned int size,
/* We keep fp->aux from fp_old around in the new
* reallocated structure.
*/
- bpf_prog_clone_free(fp_old);
+ if (free_old)
+ bpf_prog_clone_free(fp_old);
}

return fp;
@@ -456,7 +457,7 @@ struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
* last page could have large enough tailroom.
*/
prog_adj = bpf_prog_realloc(prog, bpf_prog_size(insn_adj_cnt),
- GFP_USER);
+ GFP_USER, false);
if (!prog_adj)
return ERR_PTR(-ENOMEM);

@@ -1150,6 +1151,8 @@ struct bpf_prog *bpf_jit_blind_constants(struct bpf_prog *prog)
return tmp;
}

+ if (tmp != clone)
+ bpf_prog_clone_free(clone);
clone = tmp;
insn_delta = rewritten - 1;

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 41109f49b724..e75b933f69e4 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -11855,7 +11855,10 @@ static int opt_subreg_zext_lo32_rnd_hi32(struct bpf_verifier_env *env,
new_prog = bpf_patch_insn_data(env, adj_idx, patch, patch_len);
if (!new_prog)
return -ENOMEM;
- env->prog = new_prog;
+ if (new_prog != env->prog) {
+ bpf_prog_clone_free(env->prog);
+ env->prog = new_prog;
+ }
insns = new_prog->insnsi;
aux = env->insn_aux_data;
delta += patch_len - 1;
@@ -11895,7 +11898,10 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
if (!new_prog)
return -ENOMEM;

- env->prog = new_prog;
+ if (new_prog != env->prog) {
+ bpf_prog_clone_free(env->prog);
+ env->prog = new_prog;
+ }
delta += cnt - 1;
}
}
@@ -11944,7 +11950,10 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
return -ENOMEM;

delta += cnt - 1;
- env->prog = new_prog;
+ if (new_prog != env->prog) {
+ bpf_prog_clone_free(env->prog);
+ env->prog = new_prog;
+ }
insn = new_prog->insnsi + i + delta;
continue;
}
@@ -12042,9 +12051,11 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
return -ENOMEM;

delta += cnt - 1;
-
- /* keep walking new program and skip insns we just inserted */
- env->prog = new_prog;
+ if (new_prog != env->prog) {
+ bpf_prog_clone_free(env->prog);
+ /* keep walking new program and skip insns we just inserted */
+ env->prog = new_prog;
+ }
insn = new_prog->insnsi + i + delta;
}

@@ -12419,7 +12430,10 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
return -ENOMEM;

delta += cnt - 1;
- env->prog = prog = new_prog;
+ if (new_prog != env->prog) {
+ bpf_prog_clone_free(env->prog);
+ env->prog = prog = new_prog;
+ }
insn = new_prog->insnsi + i + delta;
continue;
}
@@ -12439,7 +12453,10 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
return -ENOMEM;

delta += cnt - 1;
- env->prog = prog = new_prog;
+ if (new_prog != env->prog) {
+ bpf_prog_clone_free(env->prog);
+ env->prog = prog = new_prog;
+ }
insn = new_prog->insnsi + i + delta;
continue;
}
@@ -12492,7 +12509,10 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
return -ENOMEM;

delta += cnt - 1;
- env->prog = prog = new_prog;
+ if (new_prog != env->prog) {
+ bpf_prog_clone_free(env->prog);
+ env->prog = prog = new_prog;
+ }
insn = new_prog->insnsi + i + delta;
continue;
}
@@ -12584,7 +12604,10 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
return -ENOMEM;

delta += cnt - 1;
- env->prog = prog = new_prog;
+ if (new_prog != env->prog) {
+ bpf_prog_clone_free(env->prog);
+ env->prog = prog = new_prog;
+ }
insn = new_prog->insnsi + i + delta;
continue;
}
@@ -12623,7 +12646,10 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
return -ENOMEM;

delta += cnt - 1;
- env->prog = prog = new_prog;
+ if (new_prog != env->prog) {
+ bpf_prog_clone_free(env->prog);
+ env->prog = prog = new_prog;
+ }
insn = new_prog->insnsi + i + delta;
continue;
}
@@ -12700,7 +12726,10 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
return -ENOMEM;

delta += cnt - 1;
- env->prog = prog = new_prog;
+ if (new_prog != env->prog) {
+ bpf_prog_clone_free(env->prog);
+ env->prog = prog = new_prog;
+ }
insn = new_prog->insnsi + i + delta;
continue;
}
diff --git a/net/core/filter.c b/net/core/filter.c
index d70187ce851b..8a8d1a3ba5c2 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1268,7 +1268,7 @@ static struct bpf_prog *bpf_migrate_filter(struct bpf_prog *fp)

/* Expand fp for appending the new filter representation. */
old_fp = fp;
- fp = bpf_prog_realloc(old_fp, bpf_prog_size(new_len), 0);
+ fp = bpf_prog_realloc(old_fp, bpf_prog_size(new_len), 0, true);
if (!fp) {
/* The old_fp is still around in case we couldn't
* allocate new memory, so uncharge on that one.
--
2.25.1