From: Hui Zhu When bpf_trampoline_update() fails before modify_fentry_multi()/ unregister_fentry_multi() is called, cur_image is unchanged (cur_image == old_image) and ftrace still calls into it. Freeing old_image in that case causes a UAF. Only free old_image when it differs from cur_image. Also change bpf_trampoline_multi_detach() to return void and drop the WARN_ON_ONCE at its call site. Fixes: aef4dfa790b2 ("bpf: Add bpf_trampoline_multi_attach/detach functions") Signed-off-by: Hui Zhu --- Changelog: v4: According to the comments of bot+bpf-ci, add Fixes: and update comments of bpf_trampoline_multi_attach_free. v3: According to the comments of Jiri Olsa, drop patches 2/3 and the prog-side machinery. keep only the simplified image-side fix in bpf_trampoline_multi_attach_free() and make bpf_trampoline_multi_detach() return void. v2: Folded v1's two detach patches into patch 1. According to the comments of Jiri Olsa, Pin the prog (pinned_prog) on cur_image so it stays alive while ftrace may still call into it. Make bpf_trampoline_multi_detach() return void. Fix the same UAF in standard (non-multi) trampolines. According to the comments of sashiko, Fix the prog UAF in bpf_trampoline_multi_attach() rollback. Leak the trampoline in bpf_trampoline_put() when cur_image is left by a rollback. include/linux/bpf.h | 9 ++++----- kernel/bpf/trampoline.c | 16 +++++++++++++--- kernel/trace/bpf_trace.c | 2 +- 3 files changed, 18 insertions(+), 9 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 73bacfc6444d..3255c6f5ea6b 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1518,8 +1518,8 @@ int arch_prepare_bpf_dispatcher(void *image, void *buf, s64 *funcs, int num_func int bpf_trampoline_multi_attach(struct bpf_prog *prog, u32 *ids, struct bpf_tracing_multi_link *link); -int bpf_trampoline_multi_detach(struct bpf_prog *prog, - struct bpf_tracing_multi_link *link); +void bpf_trampoline_multi_detach(struct bpf_prog *prog, + struct bpf_tracing_multi_link *link); void bpf_trampoline_set_flags(struct bpf_trampoline *tr, u32 flags); /* @@ -1639,10 +1639,9 @@ static inline int bpf_trampoline_multi_attach(struct bpf_prog *prog, u32 *ids, { return -ENOTSUPP; } -static inline int bpf_trampoline_multi_detach(struct bpf_prog *prog, - struct bpf_tracing_multi_link *link) +static inline void bpf_trampoline_multi_detach(struct bpf_prog *prog, + struct bpf_tracing_multi_link *link) { - return -ENOTSUPP; } static inline void bpf_trampoline_set_flags(struct bpf_trampoline *tr, u32 flags) {} #endif diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c index ed7999ad6c66..e30425789487 100644 --- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -1595,7 +1595,17 @@ static void bpf_trampoline_multi_attach_init(struct bpf_trampoline *tr) static void bpf_trampoline_multi_attach_free(struct bpf_trampoline *tr) { - if (tr->multi_attach.old_image) + /* + * Only free old_image if it is no longer the active image. + * When bpf_trampoline_update() fails before modify_fentry_multi()/ + * unregister_fentry_multi() is called, cur_image is unchanged + * (cur_image == old_image) and ftrace still points to it. Freeing + * it would cause a UAF when ftrace calls into the freed memory. + * On success, cur_image is either a new image or NULL, so + * old_image != cur_image means the image is stale. + */ + if (tr->multi_attach.old_image && + tr->multi_attach.old_image != tr->cur_image) bpf_tramp_image_put(tr->multi_attach.old_image); tr->multi_attach.old_image = NULL; @@ -1719,7 +1729,8 @@ int bpf_trampoline_multi_attach(struct bpf_prog *prog, u32 *ids, return err; } -int bpf_trampoline_multi_detach(struct bpf_prog *prog, struct bpf_tracing_multi_link *link) +void bpf_trampoline_multi_detach(struct bpf_prog *prog, + struct bpf_tracing_multi_link *link) { struct bpf_tracing_multi_data *data = &link->data; struct bpf_tracing_multi_node *mnode; @@ -1749,7 +1760,6 @@ int bpf_trampoline_multi_detach(struct bpf_prog *prog, struct bpf_tracing_multi_ bpf_trampoline_put(mnode->trampoline); clear_tracing_multi_data(data); - return 0; } #undef for_each_mnode_cnt diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 891897f8a1b3..29260951aa87 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -3687,7 +3687,7 @@ static void bpf_tracing_multi_link_release(struct bpf_link *link) struct bpf_tracing_multi_link *tr_link = container_of(link, struct bpf_tracing_multi_link, link); - WARN_ON_ONCE(bpf_trampoline_multi_detach(link->prog, tr_link)); + bpf_trampoline_multi_detach(link->prog, tr_link); } static void bpf_tracing_multi_link_dealloc(struct bpf_link *link) -- 2.53.0