Create a hook for inspecting program headers during library load
Commit Message
> > On 2 October 2014 16:02, Matthew Fortune <Matthew.Fortune@imgtec.com>
> > wrote:
> > > Patch updated below. Though I did remember Joseph steering me away
> from
> > > an ifdef based interface while reworking this:
> > >
> > > https://sourceware.org/ml/libc-alpha/2014-05/msg00045.html
> > >
> > > Does this seem more appropriate?
> >
> > You could implement it using the sysdeps mechanism, e.g. see how
> > dl-irel.h and similar headers operate.
Now using sysdeps...
No regression on x86_64-linux-gnu.
Thanks,
Matthew
* elf/dl-load.c (dl-load-phdr.h): Include.
(open_verify): Add hook for phdr check.
* sysdeps/generic/dl-load-phdr.h: New file.
---
elf/dl-load.c | 6 ++++++
sysdeps/generic/dl-load-phdr.h | 32 ++++++++++++++++++++++++++++++++
2 files changed, 38 insertions(+)
create mode 100644 sysdeps/generic/dl-load-phdr.h
--
1.9.4
Comments
> * elf/dl-load.c (dl-load-phdr.h): Include.
The (...) is only for citing where you are touching. There is no function,
variable, or macro called dl-load-phdr.h, so this is not right. I'm also
not crazy about the name, since it sounds more generic than it really is.
dl-machine-reject-phdr.h would be the most specific name.
> (open_verify): Add hook for phdr check.
This should be more clear about what the change is.
> * sysdeps/generic/dl-load-phdr.h: New file.
The new file can go into elf/ instead of sysdeps/generic/, because it is
only used by code that is compiled only in the elf/ subdirectory. The
sysdeps/generic/ directory is used for files that need to be found from
builds in multiple subdirectories.
If I'd written it, the whole log entry would look like:
* elf/dl-machine-reject-phdr.h: New file.
* elf/dl-load.c: #include that.
(open_verify): Call elf_machine_reject_phdr_p and ignore the file
if that returned false.
> + if (__glibc_unlikely (
> + elf_machine_reject_phdr_p (phdr, ehdr->e_phnum, fbp->buf, fbp->len,
> + fd, loader)))
The indentation for this should look like:
if (__glibc_unlikely (elf_machine_reject_phdr_p
(phdr, ehdr->e_phnum, fbp->buf, fbp->len,
fd, loader)))
> +/* Machine-dependent ELF loader functions.
This description is too generic for what's really here.
> +#ifndef _DL_LOAD_PHDR_H
> +#define _DL_LOAD_PHDR_H
We always define these to 1 rather than empty.
You should #include <stdbool.h> here before using bool.
> +/* Return true iff ELF program headers are incompatible with the running
> + host. */
> +static inline bool
> +elf_machine_reject_phdr_p (const ElfW(Phdr) *phdr, uint_fast16_t phnum,
> + const char *buf, size_t len, int fd,
> + struct link_map *map)
It would be better to swap the order of the last two arguments, so you
don't have to integer types next to each other where transposing them
accidentally would not produce a type error.
Thanks,
Roland
@@ -41,6 +41,7 @@
#include <dl-load.h>
#include <dl-map-segments.h>
#include <dl-unmap-segments.h>
+#include <dl-load-phdr.h>
#include <endian.h>
@@ -1697,6 +1698,11 @@ open_verify (const char *name, struct filebuf *fbp, struct link_map *loader,
}
}
+ if (__glibc_unlikely (
+ elf_machine_reject_phdr_p (phdr, ehdr->e_phnum, fbp->buf, fbp->len,
+ fd, loader)))
+ goto close_and_out;
+
/* Check .note.ABI-tag if present. */
for (ph = phdr; ph < &phdr[ehdr->e_phnum]; ++ph)
if (ph->p_type == PT_NOTE && ph->p_filesz >= 32 && ph->p_align >= 4)
new file mode 100644
@@ -0,0 +1,32 @@
+/* Machine-dependent ELF loader functions.
+ Copyright (C) 2014 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#ifndef _DL_LOAD_PHDR_H
+#define _DL_LOAD_PHDR_H
+
+/* Return true iff ELF program headers are incompatible with the running
+ host. */
+static inline bool
+elf_machine_reject_phdr_p (const ElfW(Phdr) *phdr, uint_fast16_t phnum,
+ const char *buf, size_t len, int fd,
+ struct link_map *map)
+{
+ return false;
+}
+
+#endif /* dl-load-phdr.h */