[bpf-next, v2] bpf: verifier: Fix potential memleak and UAF in bpf verifier

Subsystems: bpf [core], bpf [general] (safe dynamic programs and tools), the rest

3 messages, 3 authors, 2021-07-15 · open the first message on its own page

[bpf-next, v2] bpf: verifier: Fix potential memleak and UAF in bpf verifier

From: He Fengqing <hidden>
Date: 2021-07-14 09:33:14

In bpf_patch_insn_data(), we first use the bpf_patch_insn_single() to
insert new instructions, then use adjust_insn_aux_data() to adjust
insn_aux_data. If the old env->prog have no enough room for new inserted
instructions, we use bpf_prog_realloc to construct new_prog and free the
old env->prog.

There have two errors here. First, if adjust_insn_aux_data() return
ENOMEM, we should free the new_prog. Second, if adjust_insn_aux_data()
return ENOMEM, bpf_patch_insn_data() will return NULL, and env->prog has
been freed in bpf_prog_realloc, but we will use it in bpf_check().

So in this patch, we make the adjust_insn_aux_data() never fails. In
bpf_patch_insn_data(), we first pre-malloc memory for the new
insn_aux_data, then call bpf_patch_insn_single() to insert new
instructions, at last call adjust_insn_aux_data() to adjust
insn_aux_data.

Fixes: 8041902dae52 ("bpf: adjust insn_aux_data when patching insns")

Signed-off-by: He Fengqing <redacted>

  v1->v2:
    pre-malloc memory for new insn_aux_data first, then
    adjust_insn_aux_data() will never fails.
---
 kernel/bpf/verifier.c | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index be38bb930bf1..07cf791510f1 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c

@@ -11425,10 +11425,11 @@ static void convert_pseudo_ld_imm64(struct bpf_verifier_env *env)
  * insni[off, off + cnt).  Adjust corresponding insn_aux_data by copying
  * [0, off) and [off, end) to new locations, so the patched range stays zero
  */
-static int adjust_insn_aux_data(struct bpf_verifier_env *env,
-				struct bpf_prog *new_prog, u32 off, u32 cnt)
+static void adjust_insn_aux_data(struct bpf_verifier_env *env,
+				 struct bpf_insn_aux_data *new_data,
+				 struct bpf_prog *new_prog, u32 off, u32 cnt)
 {
-	struct bpf_insn_aux_data *new_data, *old_data = env->insn_aux_data;
+	struct bpf_insn_aux_data *old_data = env->insn_aux_data;
 	struct bpf_insn *insn = new_prog->insnsi;
 	u32 old_seen = old_data[off].seen;
 	u32 prog_len;

@@ -11441,12 +11442,9 @@ static int adjust_insn_aux_data(struct bpf_verifier_env *env,
 	old_data[off].zext_dst = insn_has_def32(env, insn + off + cnt - 1);
 
 	if (cnt == 1)
-		return 0;
+		return;
 	prog_len = new_prog->len;
-	new_data = vzalloc(array_size(prog_len,
-				      sizeof(struct bpf_insn_aux_data)));
-	if (!new_data)
-		return -ENOMEM;
+
 	memcpy(new_data, old_data, sizeof(struct bpf_insn_aux_data) * off);
 	memcpy(new_data + off + cnt - 1, old_data + off,
 	       sizeof(struct bpf_insn_aux_data) * (prog_len - off - cnt + 1));

@@ -11457,7 +11455,7 @@ static int adjust_insn_aux_data(struct bpf_verifier_env *env,
 	}
 	env->insn_aux_data = new_data;
 	vfree(old_data);
-	return 0;
+	return;
 }
 
 static void adjust_subprog_starts(struct bpf_verifier_env *env, u32 off, u32 len)

@@ -11492,6 +11490,14 @@ static struct bpf_prog *bpf_patch_insn_data(struct bpf_verifier_env *env, u32 of
 					    const struct bpf_insn *patch, u32 len)
 {
 	struct bpf_prog *new_prog;
+	struct bpf_insn_aux_data *new_data = NULL;
+
+	if (len > 1) {
+		new_data = vzalloc(array_size(env->prog->len + len - 1,
+					      sizeof(struct bpf_insn_aux_data)));
+		if (!new_data)
+			return NULL;
+	}
 
 	new_prog = bpf_patch_insn_single(env->prog, off, patch, len);
 	if (IS_ERR(new_prog)) {

@@ -11499,10 +11505,12 @@ 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);
+		if (new_data)
+			vfree(new_data);
+
 		return NULL;
 	}
-	if (adjust_insn_aux_data(env, new_prog, off, len))
-		return NULL;
+	adjust_insn_aux_data(env, new_data, new_prog, off, len);
 	adjust_subprog_starts(env, off, len);
 	adjust_poke_descs(new_prog, off, len);
 	return new_prog;

-- 
2.25.1

Re: [bpf-next, v2] bpf: verifier: Fix potential memleak and UAF in bpf verifier

From: Song Liu <song@kernel.org>
Date: 2021-07-15 00:54:59

On Wed, Jul 14, 2021 at 2:33 AM He Fengqing [off-list ref] wrote:

In bpf_patch_insn_data(), we first use the bpf_patch_insn_single() to
insert new instructions, then use adjust_insn_aux_data() to adjust
insn_aux_data. If the old env->prog have no enough room for new inserted
instructions, we use bpf_prog_realloc to construct new_prog and free the
old env->prog.

There have two errors here. First, if adjust_insn_aux_data() return
ENOMEM, we should free the new_prog. Second, if adjust_insn_aux_data()
return ENOMEM, bpf_patch_insn_data() will return NULL, and env->prog has
been freed in bpf_prog_realloc, but we will use it in bpf_check().

So in this patch, we make the adjust_insn_aux_data() never fails. In
bpf_patch_insn_data(), we first pre-malloc memory for the new
insn_aux_data, then call bpf_patch_insn_single() to insert new
instructions, at last call adjust_insn_aux_data() to adjust
insn_aux_data.

Fixes: 8041902dae52 ("bpf: adjust insn_aux_data when patching insns")

Signed-off-by: He Fengqing <redacted>

Acked-by: Song Liu <redacted>

with one nitpick below.

quoted hunk

  v1->v2:
    pre-malloc memory for new insn_aux_data first, then
    adjust_insn_aux_data() will never fails.
---
 kernel/bpf/verifier.c | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index be38bb930bf1..07cf791510f1 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c

@@ -11425,10 +11425,11 @@ static void convert_pseudo_ld_imm64(struct bpf_verifier_env *env)
  * insni[off, off + cnt).  Adjust corresponding insn_aux_data by copying
  * [0, off) and [off, end) to new locations, so the patched range stays zero
  */
-static int adjust_insn_aux_data(struct bpf_verifier_env *env,
-                               struct bpf_prog *new_prog, u32 off, u32 cnt)
+static void adjust_insn_aux_data(struct bpf_verifier_env *env,
+                                struct bpf_insn_aux_data *new_data,
+                                struct bpf_prog *new_prog, u32 off, u32 cnt)
 {
-       struct bpf_insn_aux_data *new_data, *old_data = env->insn_aux_data;
+       struct bpf_insn_aux_data *old_data = env->insn_aux_data;
        struct bpf_insn *insn = new_prog->insnsi;
        u32 old_seen = old_data[off].seen;
        u32 prog_len;

@@ -11441,12 +11442,9 @@ static int adjust_insn_aux_data(struct bpf_verifier_env *env,
        old_data[off].zext_dst = insn_has_def32(env, insn + off + cnt - 1);

        if (cnt == 1)
-               return 0;
+               return;
        prog_len = new_prog->len;
-       new_data = vzalloc(array_size(prog_len,
-                                     sizeof(struct bpf_insn_aux_data)));
-       if (!new_data)
-               return -ENOMEM;
+
        memcpy(new_data, old_data, sizeof(struct bpf_insn_aux_data) * off);
        memcpy(new_data + off + cnt - 1, old_data + off,
               sizeof(struct bpf_insn_aux_data) * (prog_len - off - cnt + 1));

@@ -11457,7 +11455,7 @@ static int adjust_insn_aux_data(struct bpf_verifier_env *env,
        }
        env->insn_aux_data = new_data;
        vfree(old_data);
-       return 0;
+       return;

No need to say return here.

quoted hunk

 }

 static void adjust_subprog_starts(struct bpf_verifier_env *env, u32 off, u32 len)

@@ -11492,6 +11490,14 @@ static struct bpf_prog *bpf_patch_insn_data(struct bpf_verifier_env *env, u32 of
                                            const struct bpf_insn *patch, u32 len)
 {
        struct bpf_prog *new_prog;
+       struct bpf_insn_aux_data *new_data = NULL;
+
+       if (len > 1) {
+               new_data = vzalloc(array_size(env->prog->len + len - 1,
+                                             sizeof(struct bpf_insn_aux_data)));
+               if (!new_data)
+                       return NULL;
+       }

        new_prog = bpf_patch_insn_single(env->prog, off, patch, len);
        if (IS_ERR(new_prog)) {
@@ -11499,10 +11505,12 @@ 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);
+               if (new_data)
+                       vfree(new_data);
+
                return NULL;
        }
-       if (adjust_insn_aux_data(env, new_prog, off, len))
-               return NULL;
+       adjust_insn_aux_data(env, new_data, new_prog, off, len);
        adjust_subprog_starts(env, off, len);
        adjust_poke_descs(new_prog, off, len);
        return new_prog;
--

2.25.1

Re: [bpf-next, v2] bpf: verifier: Fix potential memleak and UAF in bpf verifier

From: Alexei Starovoitov <hidden>
Date: 2021-07-15 01:34:34

On Wed, Jul 14, 2021 at 5:54 PM Song Liu [off-list ref] wrote:

quoted

-       return 0;
+       return;

No need to say return here.

quoted

 }

 static void adjust_subprog_starts(struct bpf_verifier_env *env, u32 off, u32 len)

@@ -11492,6 +11490,14 @@ static struct bpf_prog *bpf_patch_insn_data(struct bpf_verifier_env *env, u32 of
                                            const struct bpf_insn *patch, u32 len)
 {
        struct bpf_prog *new_prog;
+       struct bpf_insn_aux_data *new_data = NULL;
+
+       if (len > 1) {
+               new_data = vzalloc(array_size(env->prog->len + len - 1,
+                                             sizeof(struct bpf_insn_aux_data)));
+               if (!new_data)
+                       return NULL;

I removed the redundant 'return' that Song pointed out and the
redundant 'if' above.
And applied to bpf-next.
Though it's a fix, I think it's ok to go via bpf-next, since even
syzbot didn't find it.

`h`	back out one level
`j`	next message in thread
`k`	previous message in thread
`l`	drill in
`Esc`	close help / fold thread tree
`?`	toggle this help