Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: - [Critical] bpf: prog refcount underflow and fd leak in link_create() on log error --
commit 56fa3f4abf91b9651c1cd02884b19754bd9ebcb5 Author: Leon Hwang <[email protected]> bpf: Add syscall common attrs support for link_create This commit adds syscall common attributes support to link_create(), creating and finalizing an internal verifier log instance and reporting error messages for an invalid prog_fd or attach_type. Link: https://lore.kernel.org/bpf/[email protected]/ > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c > index 0f27604a54aae..252b479937a4d 100644 > --- a/kernel/bpf/syscall.c > +++ b/kernel/bpf/syscall.c > @@ -5839,10 +5839,13 @@ static int bpf_map_do_batch(const union bpf_attr > *attr, > } > > #define BPF_LINK_CREATE_LAST_FIELD link_create.uprobe_multi.path_fd > -static int link_create(union bpf_attr *attr, bpfptr_t uattr) > +static int link_create(union bpf_attr *attr, bpfptr_t uattr, struct > bpf_common_attr *attr_common, > + bpfptr_t uattr_common, u32 size_common) > { > + struct bpf_verifier_log *log; > + struct bpf_log_attr attr_log; > struct bpf_prog *prog; > - int ret; > + int ret, err; > > if (CHECK_ATTR(BPF_LINK_CREATE)) > return -EINVAL; > @@ -5850,14 +5853,24 @@ static int link_create(union bpf_attr *attr, bpfptr_t > uattr) > if (attr->link_create.attach_type == BPF_STRUCT_OPS) > return bpf_struct_ops_link_create(attr); > > + log = bpf_log_attr_create_vlog(&attr_log, attr_common, uattr_common, > size_common); > + if (IS_ERR(log)) > + return PTR_ERR(log); > + > prog = bpf_prog_get(attr->link_create.prog_fd); > - if (IS_ERR(prog)) > - return PTR_ERR(prog); > + if (IS_ERR(prog)) { > + bpf_log(log, "Invalid prog_fd.\n"); > + ret = PTR_ERR(prog); > + prog = NULL; > + goto out; > + } > > ret = bpf_prog_attach_check_attach_type(prog, > attr->link_create.attach_type); > - if (ret) > + if (ret) { > + bpf_log(log, "Invalid attach_type.\n"); > goto out; > + } > > switch (prog->type) { > case BPF_PROG_TYPE_CGROUP_SKB: > @@ -5940,7 +5953,14 @@ static int link_create(union bpf_attr *attr, bpfptr_t > uattr) > } > > out: > - if (ret < 0) > + /* preserve original error even if log finalization is successful */ > + err = bpf_log_attr_finalize(&attr_log, log); > + if (err) > + ret = err; > + > + kfree(log); > + > + if (ret < 0 && prog) > bpf_prog_put(prog); > return ret; > } [Severity: Critical] Can this underflow the refcount on prog and leak the newly installed link file descriptor if bpf_log_attr_finalize() fails after link attachment succeeds? When one of the link attach helpers in switch (prog->type) succeeds, it transfers ownership of the prog reference acquired by bpf_prog_get() to link->prog and calls bpf_link_settle() (or bpf_link_new_fd()), which installs the file descriptor via fd_install() and returns the non-negative fd in ret. At the out label, bpf_log_attr_finalize() is then called: kernel/bpf/log.c:bpf_log_attr_finalize() { err = bpf_vlog_finalize(log, &log_true_size); if (attr->offsetof_true_size && copy_to_bpfptr_offset(attr->uattr, attr->offsetof_true_size, &log_true_size, sizeof(log_true_size))) return -EFAULT; return err; } If uattr_common was passed with size_common large enough to include log_true_size and resides in read-only memory (or is unmapped before finalization), copy_to_bpfptr_offset() returns -EFAULT even when nothing was logged. In link_create(), ret is then overwritten with -EFAULT, causing if (ret < 0 && prog) to call bpf_prog_put(prog) on the reference that is now owned by the active bpf_link. When the installed link fd is later closed, bpf_link_free() -> bpf_link_dealloc() will call bpf_prog_put(link->prog) a second time: kernel/bpf/syscall.c:bpf_link_dealloc() { if (link->prog) bpf_prog_put(link->prog); ... } Should the ret < 0 check for bpf_prog_put(prog) happen before ret is overwritten by err from bpf_log_attr_finalize(), or should log finalization be handled before settling the link? [ ... ] -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=1
