From 14dd70e2b33941f1f7663969574278873c9e3d35 Mon Sep 17 00:00:00 2001 From: David Gibson Date: Fri, 8 Nov 2024 13:53:29 +1100 Subject: [PATCH] linux_dep: Fix CLOSE_RANGE_UNSHARE availability handling If CLOSE_RANGE_UNSHARE isn't defined, we define a fallback version of close_range() which is a (successful) no-op. This is broken in several ways: * It doesn't actually fix compile if using old kernel headers, because the caller of close_range() still directly uses CLOSE_RANGE_UNSHARE unprotected by ifdefs * Even if it did fix the compile, it means inconsistent behaviour between a compile time failure to find the value (we silently don't close files) and a runtime failure (we die with an error from close_range()) * Silently not closing the files we intend to close for security reasons is probably not a good idea in any case We don't want to simply error if close_range() or CLOSE_RANGE_UNSHARE isn't available, because that would require running on kernel >= 5.9. On the other hand there's not really any other way to flush all possible fds leaked by the parent (close() in a loop takes over a minute). So in this case print a warning and carry on. As bonus this fixes a cppcheck error I see with some different options I'm looking to apply in future. Signed-off-by: David Gibson Signed-off-by: Stefano Brivio --- linux_dep.h | 12 ++++-------- util.c | 16 ++++++++++++++-- 2 files changed, 18 insertions(+), 10 deletions(-) diff --git a/linux_dep.h b/linux_dep.h index 3a41e42..240f50a 100644 --- a/linux_dep.h +++ b/linux_dep.h @@ -127,22 +127,18 @@ struct tcp_info_linux { #include -#ifdef CLOSE_RANGE_UNSHARE /* Linux kernel >= 5.9 */ /* glibc < 2.34 and musl as of 1.2.5 need these */ #ifndef SYS_close_range #define SYS_close_range 436 #endif +#ifndef CLOSE_RANGE_UNSHARE /* Linux kernel < 5.9 */ +#define CLOSE_RANGE_UNSHARE (1U << 1) +#endif + __attribute__ ((weak)) /* cppcheck-suppress funcArgNamesDifferent */ int close_range(unsigned int first, unsigned int last, int flags) { return syscall(SYS_close_range, first, last, flags); } -#else -/* No reasonable fallback option */ -/* cppcheck-suppress funcArgNamesDifferent */ -int close_range(unsigned int first, unsigned int last, int flags) { - return 0; -} -#endif #endif /* LINUX_DEP_H */ diff --git a/util.c b/util.c index 913f34b..126dedb 100644 --- a/util.c +++ b/util.c @@ -738,8 +738,20 @@ void close_open_files(int argc, char **argv) rc = close_range(fd + 1, ~0U, CLOSE_RANGE_UNSHARE); } - if (rc) - die_perror("Failed to close files leaked by parent"); + if (rc) { + if (errno == ENOSYS || errno == EINVAL) { + /* This probably means close_range() or the + * CLOSE_RANGE_UNSHARE flag is not supported by the + * kernel. Not much we can do here except carry on and + * hope for the best. + */ + warn( +"Can't use close_range() to ensure no files leaked by parent"); + } else { + die_perror("Failed to close files leaked by parent"); + } + } + } /**