From f468e83c8519b4ceb1b7742098a413f0b0c3d8fd Mon Sep 17 00:00:00 2001 From: Daniel Xu Date: Mon, 30 Dec 2024 14:31:22 -0700 Subject: [PATCH] libbpf: Set MFD_NOEXEC_SEAL when creating memfd Starting from 105ff5339f49 ("mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC") and until 1717449b4417 ("memfd: drop warning for missing exec-related flags"), the kernel would print a warning if neither MFD_NOEXEC_SEAL nor MFD_EXEC is set in memfd_create(). If libbpf runs on on a kernel between these two commits (eg. on an improperly backported system), it'll trigger this warning. To avoid this warning (and also be more secure), explicitly set MFD_NOEXEC_SEAL. But since libbpf can be run on potentially very old kernels, leave a fallback for kernels without MFD_NOEXEC_SEAL support. Signed-off-by: Daniel Xu Link: https://lore.kernel.org/r/6e62c2421ad7eb1da49cbf16da95aaaa7f94d394.1735594195.git.dxu@dxuuu.xyz Signed-off-by: Alexei Starovoitov --- src/libbpf.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/src/libbpf.c b/src/libbpf.c index 66173dd..46492cc 100644 --- a/src/libbpf.c +++ b/src/libbpf.c @@ -1731,12 +1731,24 @@ static int sys_memfd_create(const char *name, unsigned flags) #ifndef MFD_CLOEXEC #define MFD_CLOEXEC 0x0001U #endif +#ifndef MFD_NOEXEC_SEAL +#define MFD_NOEXEC_SEAL 0x0008U +#endif static int create_placeholder_fd(void) { + unsigned int flags = MFD_CLOEXEC | MFD_NOEXEC_SEAL; + const char *name = "libbpf-placeholder-fd"; int fd; - fd = ensure_good_fd(sys_memfd_create("libbpf-placeholder-fd", MFD_CLOEXEC)); + fd = ensure_good_fd(sys_memfd_create(name, flags)); + if (fd >= 0) + return fd; + else if (errno != EINVAL) + return -errno; + + /* Possibly running on kernel without MFD_NOEXEC_SEAL */ + fd = ensure_good_fd(sys_memfd_create(name, flags & ~MFD_NOEXEC_SEAL)); if (fd < 0) return -errno; return fd;