| Message ID | 20190301194919.2856458-1-kafai@fb.com |
|---|---|
| State | Changes Requested |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | Fix bpf_tcp_sock and bpf_sk_fullsock issue related to bpf_sk_release | expand |
> On Mar 1, 2019, at 11:49 AM, Martin KaFai Lau <kafai@fb.com> wrote: > > Lorenz Bauer [thanks!] reported that a ptr returned by bpf_tcp_sock(sk) > can still be accessed after bpf_sk_release(sk). > Both bpf_tcp_sock() and bpf_sk_fullsock() have the same issue. > This patch addresses them together. > > A simple reproducer looks like this: > > sk = bpf_sk_lookup_tcp(); > /* if (!sk) ... */ > tp = bpf_tcp_sock(sk); > /* if (!tp) ... */ > bpf_sk_release(sk); > snd_cwnd = tp->snd_cwnd; /* oops! The verifier does not complain. */ > > The problem is the verifier did not scrub the register's states of > the tcp_sock ptr (tp) after bpf_sk_release(sk). > > [ Note that when calling bpf_tcp_sock(sk), the sk is not always > refcount-acquired. e.g. bpf_tcp_sock(skb->sk). The verifier works > fine for this case. ] > > Currently, the verifier does not track if a helper's return ptr (in REG_0) > is "carry"-ing one of its argument's refcount status. To carry this info, > the reg1->id needs to be stored in reg0. The reg0->id has already > been used for NULL checking purpose. Hence, a new "refcount_id" > is needed in "struct bpf_reg_state". > > With refcount_id, when bpf_sk_release(sk) is called, the verifier can scrub > all reg states which has a refcount_id match. It is done with the changes > in release_reg_references(). > > When acquiring and releasing a refcount, the reg->id is still used. > Hence, we cannot do "bpf_sk_release(tp)" in the above reproducer > example. > > Misc change notes: > - With the new refcount_id, reg_is_refcounted() test can now be > done with "reg->refcount_id && reg->id == reg->refcount_id" instead of > testing the ptr type. > > The type_is_refcounted() and type_is_refcounted_or_null() > are no longer needed, so removed. > > - An anonymous struct is added to bpf_call_arg_meta to store > the reg->id and reg->refcount_id of the arg. Otherwise, > they will be unavailable after check_helper_call() > has cleared all CALLER_SAVED_REGS. > > - The check_func_arg() can only allow one refcount-ed arg. It is > guaranteed by check_refcount_ok() which ensures at most one arg can be > refcount-ed. Hence, it is a verifier internal error if >1 refcount arg > found in check_func_arg(). > > - The check_func_arg() also complains if a "is_acquire_function(func_id)" > helper is having a refcount-ed arg. No func_id is doing this now > and should have been rejected earlier, so it is treated as > verifier internal error also. > > - In check_func_arg(), the "!reg->id" check is removed under > the ARG_PTR_TO_SOCKET case. It is because a PTR_TO_SOCKET > can be obtained from bpf_sk_fullsock() and it does not > take a refcount. The verifier will still complain during > release_reference() but it does not treat it as a > verifier internal error anymore. > > - In release_reference(), release_reference_state() is called > first to ensure a match on "reg->id" can be found before > scrubbing the reg states with release_reg_references(). > > Fixes: 655a51e536c0 ("bpf: Add struct bpf_tcp_sock and BPF_FUNC_tcp_sock") > Cc: Lorenz Bauer <lmb@cloudflare.com> > Reported-by: Lorenz Bauer <lmb@cloudflare.com> > Signed-off-by: Martin KaFai Lau <kafai@fb.com> Acked-by: Song Liu <songliubraving@fb.com> > --- > include/linux/bpf_verifier.h | 9 ++++ > kernel/bpf/verifier.c | 86 ++++++++++++++++++++++-------------- > 2 files changed, 61 insertions(+), 34 deletions(-) > > diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h > index 69f7a3449eda..b7698d0534cb 100644 > --- a/include/linux/bpf_verifier.h > +++ b/include/linux/bpf_verifier.h > @@ -66,6 +66,15 @@ struct bpf_reg_state { > * same reference to the socket, to determine proper reference freeing. > */ > u32 id; > + /* For PTR_TO_SOCKET and PTR_TO_TCP_SOCK, this ptr may not actually > + * hold a refcount of a socket but instead it is a ptr > + * returned from a helper which is based on its refcount-ed > + * ptr argument (e.g. bpf_tcp_sock()). > + * "refcount_id" stores which refcount-ed argument it > + * originally derived from. When this original argument's > + * refcount is released, this ptr will also be invalidated. > + */ > + u32 refcount_id; > /* For scalar types (SCALAR_VALUE), this represents our knowledge of > * the actual value. > * For pointer types, this represents the variable part of the offset > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 1b9496c41383..d9cf7963f006 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -212,7 +212,10 @@ struct bpf_call_arg_meta { > int access_size; > s64 msize_smax_value; > u64 msize_umax_value; > - int ptr_id; > + struct { > + int id; > + int refcount_id; > + } refcount_reg; > int func_id; > }; > > @@ -346,19 +349,9 @@ static bool reg_type_may_be_null(enum bpf_reg_type type) > type == PTR_TO_TCP_SOCK_OR_NULL; > } > > -static bool type_is_refcounted(enum bpf_reg_type type) > -{ > - return type == PTR_TO_SOCKET; > -} > - > -static bool type_is_refcounted_or_null(enum bpf_reg_type type) > -{ > - return type == PTR_TO_SOCKET || type == PTR_TO_SOCKET_OR_NULL; > -} > - > static bool reg_is_refcounted(const struct bpf_reg_state *reg) > { > - return type_is_refcounted(reg->type); > + return reg->refcount_id && reg->id == reg->refcount_id; > } > > static bool reg_may_point_to_spin_lock(const struct bpf_reg_state *reg) > @@ -367,14 +360,10 @@ static bool reg_may_point_to_spin_lock(const struct bpf_reg_state *reg) > map_value_has_spin_lock(reg->map_ptr); > } > > -static bool reg_is_refcounted_or_null(const struct bpf_reg_state *reg) > -{ > - return type_is_refcounted_or_null(reg->type); > -} > - > static bool arg_type_is_refcounted(enum bpf_arg_type type) > { > - return type == ARG_PTR_TO_SOCKET; > + return type == ARG_PTR_TO_SOCKET || > + type == ARG_PTR_TO_SOCK_COMMON; > } > > /* Determine whether the function releases some resources allocated by another > @@ -392,6 +381,12 @@ static bool is_acquire_function(enum bpf_func_id func_id) > func_id == BPF_FUNC_sk_lookup_udp; > } > > +static bool is_refcount_carrying_function(enum bpf_func_id func_id) > +{ > + return func_id == BPF_FUNC_tcp_sock || > + func_id == BPF_FUNC_sk_fullsock; > +} > + > /* string representation of 'enum bpf_reg_type' */ > static const char * const reg_type_str[] = { > [NOT_INIT] = "?", > @@ -465,7 +460,8 @@ static void print_verifier_state(struct bpf_verifier_env *env, > if (t == PTR_TO_STACK) > verbose(env, ",call_%d", func(env, reg)->callsite); > } else { > - verbose(env, "(id=%d", reg->id); > + verbose(env, "(id=%d refcount_id=%d", reg->id, > + reg->refcount_id); > if (t != SCALAR_VALUE) > verbose(env, ",off=%d", reg->off); > if (type_is_pkt_pointer(t)) > @@ -2418,12 +2414,6 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno, > expected_type = PTR_TO_SOCKET; > if (type != expected_type) > goto err_type; > - if (meta->ptr_id || !reg->id) { > - verbose(env, "verifier internal error: mismatched references meta=%d, reg=%d\n", > - meta->ptr_id, reg->id); > - return -EFAULT; > - } > - meta->ptr_id = reg->id; > } else if (arg_type == ARG_PTR_TO_SPIN_LOCK) { > if (meta->func_id == BPF_FUNC_spin_lock) { > if (process_spin_lock(env, regno, true)) > @@ -2532,6 +2522,26 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno, > zero_size_allowed, meta); > } > > + if (reg->refcount_id) { > + if (meta->refcount_reg.refcount_id) { > + verbose(env, "verifier internal error: more than one arg with refcount_id R%d %u %u\n", > + regno, reg->refcount_id, > + meta->refcount_reg.refcount_id); > + return -EFAULT; > + } > + > + if (is_acquire_function(meta->func_id)) { > + verbose(env, > + "verifier internal error: func %s#%d taking an already refcount-ed arg R%d\n", > + func_id_name(meta->func_id), meta->func_id, > + regno); > + return -EFAULT; > + } > + > + meta->refcount_reg.id = reg->id; > + meta->refcount_reg.refcount_id = reg->refcount_id; > + } > + > return err; > err_type: > verbose(env, "R%d type=%s expected=%s\n", regno, > @@ -2805,13 +2815,13 @@ static void release_reg_references(struct bpf_verifier_env *env, > int i; > > for (i = 0; i < MAX_BPF_REG; i++) > - if (regs[i].id == id) > + if (regs[i].refcount_id == id) > mark_reg_unknown(env, regs, i); > > bpf_for_each_spilled_reg(i, state, reg) { > if (!reg) > continue; > - if (reg_is_refcounted(reg) && reg->id == id) > + if (reg->refcount_id == id) > __mark_reg_unknown(reg); > } > } > @@ -2819,16 +2829,20 @@ static void release_reg_references(struct bpf_verifier_env *env, > /* The pointer with the specified id has released its reference to kernel > * resources. Identify all copies of the same pointer and clear the reference. > */ > -static int release_reference(struct bpf_verifier_env *env, > - struct bpf_call_arg_meta *meta) > +static int release_reference(struct bpf_verifier_env *env, int id) > { > struct bpf_verifier_state *vstate = env->cur_state; > + int err; > int i; > > + err = release_reference_state(cur_func(env), id); > + if (err) > + return err; > + > for (i = 0; i <= vstate->curframe; i++) > - release_reg_references(env, vstate->frame[i], meta->ptr_id); > + release_reg_references(env, vstate->frame[i], id); > > - return release_reference_state(cur_func(env), meta->ptr_id); > + return 0; > } > > static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn, > @@ -3093,7 +3107,7 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn > return err; > } > } else if (is_release_function(func_id)) { > - err = release_reference(env, &meta); > + err = release_reference(env, meta.refcount_reg.id); > if (err) { > verbose(env, "func %s#%d reference has not been acquired before\n", > func_id_name(func_id), func_id); > @@ -3156,6 +3170,7 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn > return id; > /* For release_reference() */ > regs[BPF_REG_0].id = id; > + regs[BPF_REG_0].refcount_id = id; > } else { > /* For mark_ptr_or_null_reg() */ > regs[BPF_REG_0].id = ++env->id_gen; > @@ -3170,6 +3185,9 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn > return -EINVAL; > } > > + if (is_refcount_carrying_function(func_id)) > + regs[BPF_REG_0].refcount_id = meta.refcount_reg.refcount_id; > + > do_refine_retval_range(regs, fn->ret_type, func_id, &meta); > > err = check_map_func_compatibility(env, meta.map_ptr, func_id); > @@ -4687,8 +4705,8 @@ static void mark_ptr_or_null_regs(struct bpf_verifier_state *vstate, u32 regno, > u32 id = regs[regno].id; > int i, j; > > - if (reg_is_refcounted_or_null(®s[regno]) && is_null) > - release_reference_state(state, id); > + if (reg_is_refcounted(®s[regno]) && is_null) > + WARN_ON_ONCE(release_reference_state(state, id)); > > for (i = 0; i < MAX_BPF_REG; i++) > mark_ptr_or_null_reg(state, ®s[i], id, is_null); > -- > 2.17.1 >
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 69f7a3449eda..b7698d0534cb 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -66,6 +66,15 @@ struct bpf_reg_state { * same reference to the socket, to determine proper reference freeing. */ u32 id; + /* For PTR_TO_SOCKET and PTR_TO_TCP_SOCK, this ptr may not actually + * hold a refcount of a socket but instead it is a ptr + * returned from a helper which is based on its refcount-ed + * ptr argument (e.g. bpf_tcp_sock()). + * "refcount_id" stores which refcount-ed argument it + * originally derived from. When this original argument's + * refcount is released, this ptr will also be invalidated. + */ + u32 refcount_id; /* For scalar types (SCALAR_VALUE), this represents our knowledge of * the actual value. * For pointer types, this represents the variable part of the offset diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 1b9496c41383..d9cf7963f006 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -212,7 +212,10 @@ struct bpf_call_arg_meta { int access_size; s64 msize_smax_value; u64 msize_umax_value; - int ptr_id; + struct { + int id; + int refcount_id; + } refcount_reg; int func_id; }; @@ -346,19 +349,9 @@ static bool reg_type_may_be_null(enum bpf_reg_type type) type == PTR_TO_TCP_SOCK_OR_NULL; } -static bool type_is_refcounted(enum bpf_reg_type type) -{ - return type == PTR_TO_SOCKET; -} - -static bool type_is_refcounted_or_null(enum bpf_reg_type type) -{ - return type == PTR_TO_SOCKET || type == PTR_TO_SOCKET_OR_NULL; -} - static bool reg_is_refcounted(const struct bpf_reg_state *reg) { - return type_is_refcounted(reg->type); + return reg->refcount_id && reg->id == reg->refcount_id; } static bool reg_may_point_to_spin_lock(const struct bpf_reg_state *reg) @@ -367,14 +360,10 @@ static bool reg_may_point_to_spin_lock(const struct bpf_reg_state *reg) map_value_has_spin_lock(reg->map_ptr); } -static bool reg_is_refcounted_or_null(const struct bpf_reg_state *reg) -{ - return type_is_refcounted_or_null(reg->type); -} - static bool arg_type_is_refcounted(enum bpf_arg_type type) { - return type == ARG_PTR_TO_SOCKET; + return type == ARG_PTR_TO_SOCKET || + type == ARG_PTR_TO_SOCK_COMMON; } /* Determine whether the function releases some resources allocated by another @@ -392,6 +381,12 @@ static bool is_acquire_function(enum bpf_func_id func_id) func_id == BPF_FUNC_sk_lookup_udp; } +static bool is_refcount_carrying_function(enum bpf_func_id func_id) +{ + return func_id == BPF_FUNC_tcp_sock || + func_id == BPF_FUNC_sk_fullsock; +} + /* string representation of 'enum bpf_reg_type' */ static const char * const reg_type_str[] = { [NOT_INIT] = "?", @@ -465,7 +460,8 @@ static void print_verifier_state(struct bpf_verifier_env *env, if (t == PTR_TO_STACK) verbose(env, ",call_%d", func(env, reg)->callsite); } else { - verbose(env, "(id=%d", reg->id); + verbose(env, "(id=%d refcount_id=%d", reg->id, + reg->refcount_id); if (t != SCALAR_VALUE) verbose(env, ",off=%d", reg->off); if (type_is_pkt_pointer(t)) @@ -2418,12 +2414,6 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno, expected_type = PTR_TO_SOCKET; if (type != expected_type) goto err_type; - if (meta->ptr_id || !reg->id) { - verbose(env, "verifier internal error: mismatched references meta=%d, reg=%d\n", - meta->ptr_id, reg->id); - return -EFAULT; - } - meta->ptr_id = reg->id; } else if (arg_type == ARG_PTR_TO_SPIN_LOCK) { if (meta->func_id == BPF_FUNC_spin_lock) { if (process_spin_lock(env, regno, true)) @@ -2532,6 +2522,26 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno, zero_size_allowed, meta); } + if (reg->refcount_id) { + if (meta->refcount_reg.refcount_id) { + verbose(env, "verifier internal error: more than one arg with refcount_id R%d %u %u\n", + regno, reg->refcount_id, + meta->refcount_reg.refcount_id); + return -EFAULT; + } + + if (is_acquire_function(meta->func_id)) { + verbose(env, + "verifier internal error: func %s#%d taking an already refcount-ed arg R%d\n", + func_id_name(meta->func_id), meta->func_id, + regno); + return -EFAULT; + } + + meta->refcount_reg.id = reg->id; + meta->refcount_reg.refcount_id = reg->refcount_id; + } + return err; err_type: verbose(env, "R%d type=%s expected=%s\n", regno, @@ -2805,13 +2815,13 @@ static void release_reg_references(struct bpf_verifier_env *env, int i; for (i = 0; i < MAX_BPF_REG; i++) - if (regs[i].id == id) + if (regs[i].refcount_id == id) mark_reg_unknown(env, regs, i); bpf_for_each_spilled_reg(i, state, reg) { if (!reg) continue; - if (reg_is_refcounted(reg) && reg->id == id) + if (reg->refcount_id == id) __mark_reg_unknown(reg); } } @@ -2819,16 +2829,20 @@ static void release_reg_references(struct bpf_verifier_env *env, /* The pointer with the specified id has released its reference to kernel * resources. Identify all copies of the same pointer and clear the reference. */ -static int release_reference(struct bpf_verifier_env *env, - struct bpf_call_arg_meta *meta) +static int release_reference(struct bpf_verifier_env *env, int id) { struct bpf_verifier_state *vstate = env->cur_state; + int err; int i; + err = release_reference_state(cur_func(env), id); + if (err) + return err; + for (i = 0; i <= vstate->curframe; i++) - release_reg_references(env, vstate->frame[i], meta->ptr_id); + release_reg_references(env, vstate->frame[i], id); - return release_reference_state(cur_func(env), meta->ptr_id); + return 0; } static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn, @@ -3093,7 +3107,7 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn return err; } } else if (is_release_function(func_id)) { - err = release_reference(env, &meta); + err = release_reference(env, meta.refcount_reg.id); if (err) { verbose(env, "func %s#%d reference has not been acquired before\n", func_id_name(func_id), func_id); @@ -3156,6 +3170,7 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn return id; /* For release_reference() */ regs[BPF_REG_0].id = id; + regs[BPF_REG_0].refcount_id = id; } else { /* For mark_ptr_or_null_reg() */ regs[BPF_REG_0].id = ++env->id_gen; @@ -3170,6 +3185,9 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn return -EINVAL; } + if (is_refcount_carrying_function(func_id)) + regs[BPF_REG_0].refcount_id = meta.refcount_reg.refcount_id; + do_refine_retval_range(regs, fn->ret_type, func_id, &meta); err = check_map_func_compatibility(env, meta.map_ptr, func_id); @@ -4687,8 +4705,8 @@ static void mark_ptr_or_null_regs(struct bpf_verifier_state *vstate, u32 regno, u32 id = regs[regno].id; int i, j; - if (reg_is_refcounted_or_null(®s[regno]) && is_null) - release_reference_state(state, id); + if (reg_is_refcounted(®s[regno]) && is_null) + WARN_ON_ONCE(release_reference_state(state, id)); for (i = 0; i < MAX_BPF_REG; i++) mark_ptr_or_null_reg(state, ®s[i], id, is_null);
Lorenz Bauer [thanks!] reported that a ptr returned by bpf_tcp_sock(sk) can still be accessed after bpf_sk_release(sk). Both bpf_tcp_sock() and bpf_sk_fullsock() have the same issue. This patch addresses them together. A simple reproducer looks like this: sk = bpf_sk_lookup_tcp(); /* if (!sk) ... */ tp = bpf_tcp_sock(sk); /* if (!tp) ... */ bpf_sk_release(sk); snd_cwnd = tp->snd_cwnd; /* oops! The verifier does not complain. */ The problem is the verifier did not scrub the register's states of the tcp_sock ptr (tp) after bpf_sk_release(sk). [ Note that when calling bpf_tcp_sock(sk), the sk is not always refcount-acquired. e.g. bpf_tcp_sock(skb->sk). The verifier works fine for this case. ] Currently, the verifier does not track if a helper's return ptr (in REG_0) is "carry"-ing one of its argument's refcount status. To carry this info, the reg1->id needs to be stored in reg0. The reg0->id has already been used for NULL checking purpose. Hence, a new "refcount_id" is needed in "struct bpf_reg_state". With refcount_id, when bpf_sk_release(sk) is called, the verifier can scrub all reg states which has a refcount_id match. It is done with the changes in release_reg_references(). When acquiring and releasing a refcount, the reg->id is still used. Hence, we cannot do "bpf_sk_release(tp)" in the above reproducer example. Misc change notes: - With the new refcount_id, reg_is_refcounted() test can now be done with "reg->refcount_id && reg->id == reg->refcount_id" instead of testing the ptr type. The type_is_refcounted() and type_is_refcounted_or_null() are no longer needed, so removed. - An anonymous struct is added to bpf_call_arg_meta to store the reg->id and reg->refcount_id of the arg. Otherwise, they will be unavailable after check_helper_call() has cleared all CALLER_SAVED_REGS. - The check_func_arg() can only allow one refcount-ed arg. It is guaranteed by check_refcount_ok() which ensures at most one arg can be refcount-ed. Hence, it is a verifier internal error if >1 refcount arg found in check_func_arg(). - The check_func_arg() also complains if a "is_acquire_function(func_id)" helper is having a refcount-ed arg. No func_id is doing this now and should have been rejected earlier, so it is treated as verifier internal error also. - In check_func_arg(), the "!reg->id" check is removed under the ARG_PTR_TO_SOCKET case. It is because a PTR_TO_SOCKET can be obtained from bpf_sk_fullsock() and it does not take a refcount. The verifier will still complain during release_reference() but it does not treat it as a verifier internal error anymore. - In release_reference(), release_reference_state() is called first to ensure a match on "reg->id" can be found before scrubbing the reg states with release_reg_references(). Fixes: 655a51e536c0 ("bpf: Add struct bpf_tcp_sock and BPF_FUNC_tcp_sock") Cc: Lorenz Bauer <lmb@cloudflare.com> Reported-by: Lorenz Bauer <lmb@cloudflare.com> Signed-off-by: Martin KaFai Lau <kafai@fb.com> --- include/linux/bpf_verifier.h | 9 ++++ kernel/bpf/verifier.c | 86 ++++++++++++++++++++++-------------- 2 files changed, 61 insertions(+), 34 deletions(-)