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[2a03:2880:30ff:4::face:b00c]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a9a9157221asm462868966b.161.2024.10.23.04.38.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Oct 2024 04:38:39 -0700 (PDT) From: Breno Leitao To: Jonathan Corbet , Akinobu Mita , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Andrew Morton Cc: kernel-team@meta.com, Thomas Huth , "Paul E. McKenney" , "Borislav Petkov (AMD)" , Steven Rostedt , Xiongwei Song , Mina Almasry , Kuniyuki Iwashima , Alexander Lobakin , Oleksij Rempel , linux-doc@vger.kernel.org (open list:DOCUMENTATION), linux-kernel@vger.kernel.org (open list), netdev@vger.kernel.org (open list:NETWORKING [GENERAL]) Subject: [PATCH net-next v4] net: Implement fault injection forcing skb reallocation Date: Wed, 23 Oct 2024 04:38:01 -0700 Message-ID: <20241023113819.3395078-1-leitao@debian.org> X-Mailer: git-send-email 2.43.5 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Introduce a fault injection mechanism to force skb reallocation. The primary goal is to catch bugs related to pointer invalidation after potential skb reallocation. The fault injection mechanism aims to identify scenarios where callers retain pointers to various headers in the skb but fail to reload these pointers after calling a function that may reallocate the data. This type of bug can lead to memory corruption or crashes if the old, now-invalid pointers are used. By forcing reallocation through fault injection, we can stress-test code paths and ensure proper pointer management after potential skb reallocations. Add a hook for fault injection in the following functions: * pskb_trim_rcsum() * pskb_may_pull_reason() * pskb_trim() As the other fault injection mechanism, protect it under a debug Kconfig called CONFIG_FAIL_SKB_REALLOC. This patch was *heavily* inspired by Jakub's proposal from: https://lore.kernel.org/all/20240719174140.47a868e6@kernel.org/ CC: Akinobu Mita Suggested-by: Jakub Kicinski Signed-off-by: Breno Leitao Reviewed-by: Akinobu Mita Acked-by: Paolo Abeni Reviewed-by: Bagas Sanjaya --- Changelog: v4: * Add entry in kernel-parameters.txt (Paolo) * Renamed the config to fail_skb_realloc (Akinobu) * Fixed the documentation format (Bagas) v3: * Remove decision part of skb_might_realloc() into a new function should_fail_net_realloc_skb(). Marked it as ALLOW_ERROR_INJECTION, so it could be controlled by fail_function and BPF (Paolo) * https://lore.kernel.org/all/20241014135015.3506392-1-leitao@debian.org/ v2: * Moved the CONFIG_FAIL_SKB_FORCE_REALLOC Kconfig entry closer to other fault injection Kconfigs. (Kuniyuki Iwashima) * Create a filter mechanism (Akinobu Mita) * https://lore.kernel.org/all/20241008111358.1691157-1-leitao@debian.org/ v1: * https://lore.kernel.org/all/20241002113316.2527669-1-leitao@debian.org/ .../admin-guide/kernel-parameters.txt | 1 + .../fault-injection/fault-injection.rst | 36 ++++++ include/linux/skbuff.h | 9 ++ lib/Kconfig.debug | 10 ++ net/core/Makefile | 1 + net/core/skb_fault_injection.c | 103 ++++++++++++++++++ 6 files changed, 160 insertions(+) create mode 100644 net/core/skb_fault_injection.c diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentatio= n/admin-guide/kernel-parameters.txt index 1518343bbe22..2fb830453dcc 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -1546,6 +1546,7 @@ failslab=3D fail_usercopy=3D fail_page_alloc=3D + fail_skb_realloc=3D fail_make_request=3D[KNL] General fault injection mechanism. Format: ,,, diff --git a/Documentation/fault-injection/fault-injection.rst b/Documentat= ion/fault-injection/fault-injection.rst index 8b8aeea71c68..c50c8023200a 100644 --- a/Documentation/fault-injection/fault-injection.rst +++ b/Documentation/fault-injection/fault-injection.rst @@ -45,6 +45,28 @@ Available fault injection capabilities ALLOW_ERROR_INJECTION() macro, by setting debugfs entries under /sys/kernel/debug/fail_function. No boot option supported. =20 +- fail_skb_realloc + + inject skb (socket buffer) reallocation events into the network path. The + primary goal is to identify and prevent issues related to pointer + mismanagement in the network subsystem. By forcing skb reallocation at + strategic points, this feature creates scenarios where existing pointers= to + skb headers become invalid. + + When the fault is injected and the reallocation is triggered, these poin= ters + no longer reference valid memory locations. This deliberate invalidation + helps expose code paths where proper pointer updating is neglected after= a + reallocation event. + + By creating these controlled fault scenarios, the system can catch insta= nces + where stale pointers are used, potentially leading to memory corruption = or + system instability. + + To select the interface to act on, write the network name to the followi= ng file: + `/sys/kernel/debug/fail_skb_realloc/devname` + If this field is left empty (which is the default value), skb reallocati= on + will be forced on all network interfaces. + - NVMe fault injection =20 inject NVMe status code and retry flag on devices permitted by setting @@ -216,6 +238,19 @@ configuration of fault-injection capabilities. use a negative errno, you better use 'printf' instead of 'echo', e.g.: $ printf %#x -12 > retval =20 +- /sys/kernel/debug/fail_skb_realloc/devname: + + Specifies the network interface on which to force SKB reallocation= . If + left empty, SKB reallocation will be applied to all network interf= aces. + + Example usage:: + + # Force skb reallocation on eth0 + echo "eth0" > /sys/kernel/debug/fail_skb_realloc/devname + + # Clear the selection and force skb reallocation on all interfac= es + echo "" > /sys/kernel/debug/fail_skb_realloc/devname + Boot option ^^^^^^^^^^^ =20 @@ -227,6 +262,7 @@ use the boot option:: fail_usercopy=3D fail_make_request=3D fail_futex=3D + fail_skb_realloc=3D mmc_core.fail_request=3D,,, =20 proc entries diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 48f1e0fa2a13..285e36a5e5d7 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -2681,6 +2681,12 @@ static inline void skb_assert_len(struct sk_buff *sk= b) #endif /* CONFIG_DEBUG_NET */ } =20 +#if defined(CONFIG_FAIL_SKB_REALLOC) +void skb_might_realloc(struct sk_buff *skb); +#else +static inline void skb_might_realloc(struct sk_buff *skb) {} +#endif + /* * Add data to an sk_buff */ @@ -2781,6 +2787,7 @@ static inline enum skb_drop_reason pskb_may_pull_reason(struct sk_buff *skb, unsigned int len) { DEBUG_NET_WARN_ON_ONCE(len > INT_MAX); + skb_might_realloc(skb); =20 if (likely(len <=3D skb_headlen(skb))) return SKB_NOT_DROPPED_YET; @@ -3216,6 +3223,7 @@ static inline int __pskb_trim(struct sk_buff *skb, un= signed int len) =20 static inline int pskb_trim(struct sk_buff *skb, unsigned int len) { + skb_might_realloc(skb); return (len < skb->len) ? __pskb_trim(skb, len) : 0; } =20 @@ -3970,6 +3978,7 @@ int pskb_trim_rcsum_slow(struct sk_buff *skb, unsigne= d int len); =20 static inline int pskb_trim_rcsum(struct sk_buff *skb, unsigned int len) { + skb_might_realloc(skb); if (likely(len >=3D skb->len)) return 0; return pskb_trim_rcsum_slow(skb, len); diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 7315f643817a..52bb27115185 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -2115,6 +2115,16 @@ config FAIL_SUNRPC Provide fault-injection capability for SunRPC and its consumers. =20 +config FAIL_SKB_REALLOC + bool "Fault-injection capability forcing skb to reallocate" + depends on FAULT_INJECTION_DEBUG_FS + help + Provide fault-injection capability that forces the skb to be + reallocated, caughting possible invalid pointers to the skb. + + For more information, check + Documentation/dev-tools/fault-injection/fault-injection.rst + config FAULT_INJECTION_CONFIGFS bool "Configfs interface for fault-injection capabilities" depends on FAULT_INJECTION diff --git a/net/core/Makefile b/net/core/Makefile index 5a72a87ee0f1..d9326600e289 100644 --- a/net/core/Makefile +++ b/net/core/Makefile @@ -46,3 +46,4 @@ obj-$(CONFIG_OF) +=3D of_net.o obj-$(CONFIG_NET_TEST) +=3D net_test.o obj-$(CONFIG_NET_DEVMEM) +=3D devmem.o obj-$(CONFIG_DEBUG_NET_SMALL_RTNL) +=3D rtnl_net_debug.o +obj-$(CONFIG_FAIL_SKB_REALLOC) +=3D skb_fault_injection.o diff --git a/net/core/skb_fault_injection.c b/net/core/skb_fault_injection.c new file mode 100644 index 000000000000..21b0ea48c139 --- /dev/null +++ b/net/core/skb_fault_injection.c @@ -0,0 +1,103 @@ +// SPDX-License-Identifier: GPL-2.0-only + +#include +#include +#include +#include + +static struct { + struct fault_attr attr; + char devname[IFNAMSIZ]; + bool filtered; +} skb_realloc =3D { + .attr =3D FAULT_ATTR_INITIALIZER, + .filtered =3D false, +}; + +static bool should_fail_net_realloc_skb(struct sk_buff *skb) +{ + struct net_device *net =3D skb->dev; + + if (skb_realloc.filtered && + strncmp(net->name, skb_realloc.devname, IFNAMSIZ)) + /* device name filter set, but names do not match */ + return false; + + if (!should_fail(&skb_realloc.attr, 1)) + return false; + + return true; +} +ALLOW_ERROR_INJECTION(should_fail_net_realloc_skb, TRUE); + +void skb_might_realloc(struct sk_buff *skb) +{ + if (!should_fail_net_realloc_skb(skb)) + return; + + pskb_expand_head(skb, 0, 0, GFP_ATOMIC); +} +EXPORT_SYMBOL(skb_might_realloc); + +static int __init fail_skb_realloc_setup(char *str) +{ + return setup_fault_attr(&skb_realloc.attr, str); +} +__setup("fail_skb_realloc=3D", fail_skb_realloc_setup); + +static void reset_settings(void) +{ + skb_realloc.filtered =3D false; + memzero_explicit(&skb_realloc.devname, IFNAMSIZ); +} + +static ssize_t devname_write(struct file *file, const char __user *buffer, + size_t count, loff_t *ppos) +{ + ssize_t ret; + + reset_settings(); + ret =3D simple_write_to_buffer(&skb_realloc.devname, IFNAMSIZ, + ppos, buffer, count); + if (ret < 0) + return ret; + strim(skb_realloc.devname); + + if (strnlen(skb_realloc.devname, IFNAMSIZ)) + skb_realloc.filtered =3D true; + + return count; +} + +static ssize_t devname_read(struct file *file, + char __user *buffer, + size_t size, loff_t *ppos) +{ + if (!skb_realloc.filtered) + return 0; + + return simple_read_from_buffer(buffer, size, ppos, &skb_realloc.devname, + strlen(skb_realloc.devname)); +} + +static const struct file_operations devname_ops =3D { + .write =3D devname_write, + .read =3D devname_read, +}; + +static int __init fail_skb_realloc_debugfs(void) +{ + umode_t mode =3D S_IFREG | 0600; + struct dentry *dir; + + dir =3D fault_create_debugfs_attr("fail_skb_realloc", NULL, + &skb_realloc.attr); + if (IS_ERR(dir)) + return PTR_ERR(dir); + + debugfs_create_file("devname", mode, dir, NULL, &devname_ops); + + return 0; +} + +late_initcall(fail_skb_realloc_debugfs); --=20 2.43.5