This fixes an obscure SIGBUS error when using ELF_C_WRITE_MMAP on an ELF file that needs extending when the underlying file system is (nearly) full.

Use posix_fallocate to make sure the file content is really there. Using ftruncate might mean the file is extended, but space isn't allocated yet. This might cause a SIGBUS once we write into the mmapped space and the disk is full.

Using fallocate might fail on some file systems. posix_fallocate is required to extend the file and allocate enough space even if the underlying filesystem would normally return EOPNOTSUPP or the kernel doesn't implement the fallocate syscall. Also posix_fallocate has been in glibc since 2.1.94, while support for fallocate was only added in 2.10 and kernel 2.6.23.

Signed-off-by: Mark Wielaard mjw@redhat.com --- libelf/ChangeLog | 5 +++++ libelf/elf_update.c | 16 +++++++++++++--- 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/libelf/ChangeLog b/libelf/ChangeLog index 2d10b83..5e7b104 100644 --- a/libelf/ChangeLog +++ b/libelf/ChangeLog @@ -1,3 +1,8 @@ +2015-05-14 Mark Wielaard mjw@redhat.com + + * elf_update.c (write_file): Use possix_fallocate instead of + ftruncate to extend file if necessary. + 2015-05-13 Mark Wielaard mjw@redhat.com

* elf32_updatenull.c (default_ehdr): If e_phnum is zero then set diff --git a/libelf/elf_update.c b/libelf/elf_update.c index 54c20f5..3674e72 100644 --- a/libelf/elf_update.c +++ b/libelf/elf_update.c @@ -1,5 +1,5 @@ /* Update data structures for changes and write them out. - Copyright (C) 1999, 2000, 2001, 2002, 2004, 2005, 2006 Red Hat, Inc. + Copyright (C) 1999, 2000, 2001, 2002, 2004, 2005, 2006, 2015 Red Hat, Inc. This file is part of elfutils. Contributed by Ulrich Drepper drepper@redhat.com, 1999.

@@ -32,6 +32,7 @@ #endif

#include <libelf.h> +#include <fcntl.h> #include <unistd.h> #include <sys/mman.h> #include <sys/stat.h> @@ -56,11 +57,19 @@ write_file (Elf *elf, off_t size, int change_bo, size_t shnum) We cannot do this if this file is in an archive. We also don't do it *now* if we are shortening the file since this would prevent programs to use the data of the file in generating the - new file. We truncate the file later in this case. */ + new file. We truncate the file later in this case. + + Note we use posix_fallocate to make sure the file content is really + there. Using ftruncate might mean the file is extended, but space + isn't allocated yet. This might cause a SIGBUS once we write into + the mmapped space and the disk is full. Using fallocate might fail + on some file systems. posix_fallocate is required to extend the file + and allocate enough space even if the underlying filesystem would + normally return EOPNOTSUPP. */ if (elf->parent == NULL && (elf->maximum_size == ~((size_t) 0) || (size_t) size > elf->maximum_size) - && unlikely (ftruncate (elf->fildes, size) != 0)) + && unlikely (possix_fallocate (elf->fildes, 0, size) != 0)) { __libelf_seterrno (ELF_E_WRITE_ERROR); return -1; @@ -94,6 +103,7 @@ write_file (Elf *elf, off_t size, int change_bo, size_t shnum) size = -1; }

+ /* Reduce the file size if necessary. */ if (size != -1 && elf->parent == NULL && elf->maximum_size != ~((size_t) 0)