From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A74EC3B1EC8; Sat, 17 Oct 2026 17:21:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792257710; cv=none; b=jpuDdBLqAIFTRIsaDL6XPqvFDsQUBv+TqZc4AnQI+1pT85I+CqAksbC5XbSDtMrJFdKXBwJnrst7TohKy/xcoKlqcZvSjkEK1Yy0p7tJ8AxgDoTYRIvEc8snA3mhjeLcM+4NHTsGLZrufD9PB7gihFCZBQo60LnYmRfa260yuFs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792257710; c=relaxed/simple; bh=wG/D3x30wKN9fCO2tZxY5VbpzNSyIGTMq802Cu9V9fk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=B6tIa+9nkuXm5nZ/8Nz7kOrNzDowB+s0l2dfSSrdCnAJ7DCA1Fl40Xve1iug7tw/FknhPOY7pAkc1xuvmAlUTB46bKfnGQUNwarSQWkZYykxabGiZDR4Wv7YAcyhCEpNlstp9VwR1JLlibPY1adC1OwQJmKFaBQjCt00PlwPIQ8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=MlNiMBO+; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="MlNiMBO+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F1B3E1F000C4; Sat, 17 Oct 2026 17:21:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1792257707; bh=JxGWVnnT3Qo0xKqq0u/BsA/AwmGZNQS1/btFhTWg+Vo=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=MlNiMBO+p4sDKFQZCxN5w7ry9UT7V41NwQchCbCqxbUUt92dqw7oBHi1hPTFdEb+d tAVd+6W0dJ6wezuv7w/EC1FUQjZpPSJxwi2c6DkW1qtFO10geoLDaUbfwHyCNLGpdg Qk4OeIafKBlbqC6Y2YxvL6/G1S2XH4fTbqdYJx6U= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Eduard Zingerman , Leon Hwang , Alexei Starovoitov , Sasha Levin Subject: [PATCH 6.6 0644/1674] bpf: Prevent tailcall infinite loop caused by freplace Date: Sat, 17 Oct 2026 17:48:36 +0200 Message-ID: <20261017160447.635897281@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261017160431.119607952@linuxfoundation.org> References: <20261017160431.119607952@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Leon Hwang [ Upstream commit d6083f040d5d8f8d748462c77e90547097df936e ] There is a potential infinite loop issue that can occur when using a combination of tail calls and freplace. In an upcoming selftest, the attach target for entry_freplace of tailcall_freplace.c is subprog_tc of tc_bpf2bpf.c, while the tail call in entry_freplace leads to entry_tc. This results in an infinite loop: entry_tc -> subprog_tc -> entry_freplace --tailcall-> entry_tc. The problem arises because the tail_call_cnt in entry_freplace resets to zero each time entry_freplace is executed, causing the tail call mechanism to never terminate, eventually leading to a kernel panic. To fix this issue, the solution is twofold: 1. Prevent updating a program extended by an freplace program to a prog_array map. 2. Prevent extending a program that is already part of a prog_array map with an freplace program. This ensures that: * If a program or its subprogram has been extended by an freplace program, it can no longer be updated to a prog_array map. * If a program has been added to a prog_array map, neither it nor its subprograms can be extended by an freplace program. Moreover, an extension program should not be tailcalled. As such, return -EINVAL if the program has a type of BPF_PROG_TYPE_EXT when adding it to a prog_array map. Additionally, fix a minor code style issue by replacing eight spaces with a tab for proper formatting. Reviewed-by: Eduard Zingerman Signed-off-by: Leon Hwang Link: https://lore.kernel.org/r/20241015150207.70264-2-leon.hwang@linux.dev Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- include/linux/bpf.h | 17 +++++++++++---- kernel/bpf/arraymap.c | 26 +++++++++++++++++++++-- kernel/bpf/core.c | 1 + kernel/bpf/syscall.c | 7 +++--- kernel/bpf/trampoline.c | 47 ++++++++++++++++++++++++++++++++++------- 5 files changed, 81 insertions(+), 17 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 19aa8a5257884..5b1bc7b2ddfae 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1258,8 +1258,12 @@ int bpf_dynptr_check_size(u32 size); u32 __bpf_dynptr_size(const struct bpf_dynptr_kern *ptr); #ifdef CONFIG_BPF_JIT -int bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr); -int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr); +int bpf_trampoline_link_prog(struct bpf_tramp_link *link, + struct bpf_trampoline *tr, + struct bpf_prog *tgt_prog); +int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, + struct bpf_trampoline *tr, + struct bpf_prog *tgt_prog); struct bpf_trampoline *bpf_trampoline_get(u64 key, struct bpf_attach_target_info *tgt_info); void bpf_trampoline_put(struct bpf_trampoline *tr); @@ -1340,12 +1344,14 @@ void bpf_jit_uncharge_modmem(u32 size); bool bpf_prog_has_trampoline(const struct bpf_prog *prog); #else static inline int bpf_trampoline_link_prog(struct bpf_tramp_link *link, - struct bpf_trampoline *tr) + struct bpf_trampoline *tr, + struct bpf_prog *tgt_prog) { return -ENOTSUPP; } static inline int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, - struct bpf_trampoline *tr) + struct bpf_trampoline *tr, + struct bpf_prog *tgt_prog) { return -ENOTSUPP; } @@ -1444,6 +1450,9 @@ struct bpf_prog_aux { bool tail_call_reachable; bool xdp_has_frags; bool changes_pkt_data; + bool is_extended; /* true if extended by freplace program */ + u64 prog_array_member_cnt; /* counts how many times as member of prog_array */ + struct mutex ext_mutex; /* mutex for is_extended and prog_array_member_cnt */ /* BTF_KIND_FUNC_PROTO for valid attach_btf_id */ const struct btf_type *attach_func_proto; /* function name for valid attach_btf_id */ diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c index ec5c489ed3131..ca135fa407b85 100644 --- a/kernel/bpf/arraymap.c +++ b/kernel/bpf/arraymap.c @@ -909,22 +909,44 @@ static void *prog_fd_array_get_ptr(struct bpf_map *map, struct file *map_file, int fd) { struct bpf_prog *prog = bpf_prog_get(fd); + bool is_extended; if (IS_ERR(prog)) return prog; - if (!bpf_prog_map_compatible(map, prog)) { + if (prog->type == BPF_PROG_TYPE_EXT || + !bpf_prog_map_compatible(map, prog)) { bpf_prog_put(prog); return ERR_PTR(-EINVAL); } + mutex_lock(&prog->aux->ext_mutex); + is_extended = prog->aux->is_extended; + if (!is_extended) + prog->aux->prog_array_member_cnt++; + mutex_unlock(&prog->aux->ext_mutex); + if (is_extended) { + /* Extended prog can not be tail callee. It's to prevent a + * potential infinite loop like: + * tail callee prog entry -> tail callee prog subprog -> + * freplace prog entry --tailcall-> tail callee prog entry. + */ + bpf_prog_put(prog); + return ERR_PTR(-EBUSY); + } + return prog; } static void prog_fd_array_put_ptr(struct bpf_map *map, void *ptr, bool need_defer) { + struct bpf_prog *prog = ptr; + + mutex_lock(&prog->aux->ext_mutex); + prog->aux->prog_array_member_cnt--; + mutex_unlock(&prog->aux->ext_mutex); /* bpf_prog is freed after one RCU or tasks trace grace period */ - bpf_prog_put(ptr); + bpf_prog_put(prog); } static u32 prog_fd_array_sys_lookup_elem(void *ptr) diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index ea78ef4774198..3fc818987ef0e 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -123,6 +123,7 @@ struct bpf_prog *bpf_prog_alloc_no_stats(unsigned int size, gfp_t gfp_extra_flag INIT_LIST_HEAD_RCU(&fp->aux->ksym.lnode); mutex_init(&fp->aux->used_maps_mutex); + mutex_init(&fp->aux->ext_mutex); mutex_init(&fp->aux->dst_mutex); return fp; diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 1710391f386af..cd31c926f5da3 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -3125,7 +3125,8 @@ static void bpf_tracing_link_release(struct bpf_link *link) container_of(link, struct bpf_tracing_link, link.link); WARN_ON_ONCE(bpf_trampoline_unlink_prog(&tr_link->link, - tr_link->trampoline)); + tr_link->trampoline, + tr_link->tgt_prog)); bpf_trampoline_put(tr_link->trampoline); @@ -3260,7 +3261,7 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog, * in prog->aux * * - if prog->aux->dst_trampoline is NULL, the program has already been - * attached to a target and its initial target was cleared (below) + * attached to a target and its initial target was cleared (below) * * - if tgt_prog != NULL, the caller specified tgt_prog_fd + * target_btf_id using the link_create API. @@ -3335,7 +3336,7 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog, if (err) goto out_unlock; - err = bpf_trampoline_link_prog(&link->link, tr); + err = bpf_trampoline_link_prog(&link->link, tr, tgt_prog); if (err) { bpf_link_cleanup(&link_primer); link = NULL; diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c index 6f7968d3704eb..a75c3bdaa35ae 100644 --- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -508,7 +508,27 @@ static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog) } } -static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr) +static int bpf_freplace_check_tgt_prog(struct bpf_prog *tgt_prog) +{ + struct bpf_prog_aux *aux = tgt_prog->aux; + + guard(mutex)(&aux->ext_mutex); + if (aux->prog_array_member_cnt) + /* Program extensions can not extend target prog when the target + * prog has been updated to any prog_array map as tail callee. + * It's to prevent a potential infinite loop like: + * tgt prog entry -> tgt prog subprog -> freplace prog entry + * --tailcall-> tgt prog entry. + */ + return -EBUSY; + + aux->is_extended = true; + return 0; +} + +static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, + struct bpf_trampoline *tr, + struct bpf_prog *tgt_prog) { enum bpf_tramp_prog_type kind; struct bpf_tramp_link *link_exiting; @@ -529,6 +549,9 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_tr /* Cannot attach extension if fentry/fexit are in use. */ if (cnt) return -EBUSY; + err = bpf_freplace_check_tgt_prog(tgt_prog); + if (err) + return err; tr->extension_prog = link->link.prog; return bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP, NULL, link->link.prog->bpf_func); @@ -555,17 +578,21 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_tr return err; } -int bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr) +int bpf_trampoline_link_prog(struct bpf_tramp_link *link, + struct bpf_trampoline *tr, + struct bpf_prog *tgt_prog) { int err; mutex_lock(&tr->mutex); - err = __bpf_trampoline_link_prog(link, tr); + err = __bpf_trampoline_link_prog(link, tr, tgt_prog); mutex_unlock(&tr->mutex); return err; } -static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr) +static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, + struct bpf_trampoline *tr, + struct bpf_prog *tgt_prog) { enum bpf_tramp_prog_type kind; int err; @@ -576,6 +603,8 @@ static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_ err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP, tr->extension_prog->bpf_func, NULL); tr->extension_prog = NULL; + guard(mutex)(&tgt_prog->aux->ext_mutex); + tgt_prog->aux->is_extended = false; return err; } hlist_del_init(&link->tramp_hlist); @@ -584,12 +613,14 @@ static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_ } /* bpf_trampoline_unlink_prog() should never fail. */ -int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr) +int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link, + struct bpf_trampoline *tr, + struct bpf_prog *tgt_prog) { int err; mutex_lock(&tr->mutex); - err = __bpf_trampoline_unlink_prog(link, tr); + err = __bpf_trampoline_unlink_prog(link, tr, tgt_prog); mutex_unlock(&tr->mutex); return err; } @@ -604,7 +635,7 @@ static void bpf_shim_tramp_link_release(struct bpf_link *link) if (!shim_link->trampoline) return; - WARN_ON_ONCE(bpf_trampoline_unlink_prog(&shim_link->link, shim_link->trampoline)); + WARN_ON_ONCE(bpf_trampoline_unlink_prog(&shim_link->link, shim_link->trampoline, NULL)); bpf_trampoline_put(shim_link->trampoline); } @@ -716,7 +747,7 @@ int bpf_trampoline_link_cgroup_shim(struct bpf_prog *prog, goto err; } - err = __bpf_trampoline_link_prog(&shim_link->link, tr); + err = __bpf_trampoline_link_prog(&shim_link->link, tr, NULL); if (err) goto err; -- 2.53.0