From bc308d011ab8cc61bf1be15a2920bcd7d7b9b9d3 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Fri, 19 Jan 2024 13:02:01 -0800 Subject: [PATCH] libbpf: call dup2() syscall directly We've ran into issues with using dup2() API in production setting, where libbpf is linked into large production environment and ends up calling unintended custom implementations of dup2(). These custom implementations don't provide atomic FD replacement guarantees of dup2() syscall, leading to subtle and hard to debug issues. To prevent this in the future and guarantee that no libc implementation will do their own custom non-atomic dup2() implementation, call dup2() syscall directly with syscall(SYS_dup2). Note that some architectures don't seem to provide dup2 and have dup3 instead. Try to detect and pick best syscall. Signed-off-by: Andrii Nakryiko Acked-by: Song Liu Acked-by: Yonghong Song Link: https://lore.kernel.org/r/20240119210201.1295511-1-andrii@kernel.org Signed-off-by: Alexei Starovoitov --- tools/lib/bpf/libbpf_internal.h | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h index 27e4e320e1a69..58c547d473e00 100644 --- a/tools/lib/bpf/libbpf_internal.h +++ b/tools/lib/bpf/libbpf_internal.h @@ -15,6 +15,7 @@ #include #include #include +#include #include #include "relo_core.h" @@ -555,6 +556,15 @@ static inline int ensure_good_fd(int fd) return fd; } +static inline int sys_dup2(int oldfd, int newfd) +{ +#ifdef __NR_dup2 + return syscall(__NR_dup2, oldfd, newfd); +#else + return syscall(__NR_dup3, oldfd, newfd, 0); +#endif +} + /* Point *fixed_fd* to the same file that *tmp_fd* points to. * Regardless of success, *tmp_fd* is closed. * Whatever *fixed_fd* pointed to is closed silently. @@ -563,7 +573,7 @@ static inline int reuse_fd(int fixed_fd, int tmp_fd) { int err; - err = dup2(tmp_fd, fixed_fd); + err = sys_dup2(tmp_fd, fixed_fd); err = err < 0 ? -errno : 0; close(tmp_fd); /* clean up temporary FD */ return err; -- 2.30.2