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Avoid cancellable I/O primitives in ld.so.

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Neither the <dlfcn.h> entry points, nor lazy symbol resolution, nor
initial shared library load-up, are cancellation points, so ld.so
should exclusively use I/O primitives that are not cancellable.  We
currently achieve this by having the cancellation hooks compile as
no-ops when IS_IN(rtld); this patch changes to using exclusively
_nocancel primitives in the source code instead, which makes the
intent clearer and significantly reduces the amount of code compiled
under IS_IN(rtld) as well as IS_IN(libc) -- in particular,
elf/Makefile no longer thinks we require a copy of unwind.c in
rtld-libc.a.  (The older mechanism is preserved as a backstop.)

The bulk of the change is splitting up the files that define the
_nocancel I/O functions, so they don't also define the variants that
*are* cancellation points; after which, the existing logic for picking
out the bits of libc that need to be recompiled as part of ld.so Just
Works.  I did this for all of the _nocancel functions, not just the
ones used by ld.so, for consistency.

fcntl was a little tricky because it's only a cancellation point for
certain opcodes (F_SETLKW(64), which can block), and the existing
__fcntl_nocancel wasn't applying the FCNTL_ADJUST_CMD hook, which
strikes me as asking for trouble, especially as the only nontrivial
definition of FCNTL_ADJUST_CMD (for powerpc64) changes F_*LK* opcodes.
To fix this, fcntl_common moves to fcntl_nocancel.c along with
__fcntl_nocancel, and changes its name to the extern (but hidden)
symbol __fcntl_nocancel_adjusted, so that regular fcntl can continue
calling it.  __fcntl_nocancel now applies FCNTL_ADJUST_CMD; so that
both both fcntl.c and fcntl_nocancel.c can see it, the only nontrivial
definition moves from sysdeps/u/s/l/powerpc/powerpc64/fcntl.c to
.../powerpc64/sysdep.h and becomes entirely a macro, instead of a macro
that calls an inline function.

The nptl version of libpthread also changes a little, because its
"compat-routines" formerly included files that defined all the
_nocancel functions it uses; instead of continuing to duplicate them,
I exported the relevant ones from libc.so as GLIBC_PRIVATE.  Since the
Linux fcntl.c calls a function defined by fcntl_nocancel.c, it can no
longer be used from libpthread.so; instead, introduce a custom
forwarder, pt-fcntl.c, and export __libc_fcntl from libc.so as
GLIBC_PRIVATE.  The nios2-linux ABI doesn't include a copy of vfork()
in libpthread, and it was handling that by manipulating
libpthread-routines in .../linux/nios2/Makefile; it is cleaner to do
what other such ports do, and have a pt-vfork.S that defines no symbols.

Right now, it appears that Hurd does not implement _nocancel I/O, so
sysdeps/generic/not-cancel.h will forward everything back to the
regular functions.  This changed the names of some of the functions
that sysdeps/mach/hurd/dl-sysdep.c needs to interpose.

	* elf/dl-load.c, elf/dl-misc.c, elf/dl-profile.c, elf/rtld.c
	* sysdeps/unix/sysv/linux/dl-sysdep.c
	Include not-cancel.h.  Use __close_nocancel instead of __close,
	__open64_nocancel instead of __open, __read_nocancel instead of
	__libc_read, and __write_nocancel instead of __libc_write.

	* csu/check_fds.c (check_one_fd)
	* sysdeps/posix/fdopendir.c (__fdopendir)
	* sysdeps/posix/opendir.c (__alloc_dir): Use __fcntl_nocancel
        instead of __fcntl and/or __libc_fcntl.

	* sysdeps/unix/sysv/linux/pthread_setname.c (pthread_setname_np)
	* sysdeps/unix/sysv/linux/pthread_getname.c (pthread_getname_np)
        * sysdeps/unix/sysv/linux/i386/smp.h (is_smp_system):
	Use __open64_nocancel instead of __open_nocancel.

	* sysdeps/unix/sysv/linux/not-cancel.h: Move all of the
	hidden_proto declarations to the end and issue them if either
	IS_IN(libc) or IS_IN(rtld).
	* sysdeps/unix/sysv/linux/Makefile [subdir=io] (sysdep_routines):
	Add close_nocancel, fcntl_nocancel, nanosleep_nocancel,
	open_nocancel, open64_nocancel, openat_nocancel, pause_nocancel,
	read_nocancel, waitpid_nocancel, write_nocancel.

        * io/Versions [GLIBC_PRIVATE]: Add __libc_fcntl,
        __fcntl_nocancel, __open64_nocancel, __write_nocancel.
        * posix/Versions: Add __nanosleep_nocancel, __pause_nocancel.

        * nptl/pt-fcntl.c: New file.
        * nptl/Makefile (pthread-compat-wrappers): Remove fcntl.
        (libpthread-routines): Add pt-fcntl.
        * include/fcntl.h (__fcntl_nocancel_adjusted): New function.
        (__libc_fcntl): Remove attribute_hidden.
	* sysdeps/unix/sysv/linux/fcntl.c (__libc_fcntl): Call
	__fcntl_nocancel_adjusted, not fcntl_common.
        (__fcntl_nocancel): Move to new file fcntl_nocancel.c.
	(fcntl_common): Rename to __fcntl_nocancel_adjusted; also move
	to fcntl_nocancel.c.
	* sysdeps/unix/sysv/linux/fcntl_nocancel.c: New file.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/fcntl.c: Remove file.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h:
	Define FCNTL_ADJUST_CMD here, as a self-contained macro.

	* sysdeps/unix/sysv/linux/close.c: Move __close_nocancel to...
	* sysdeps/unix/sysv/linux/close_nocancel.c: ...this new file.
	* sysdeps/unix/sysv/linux/nanosleep.c: Move __nanosleep_nocancel to...
	* sysdeps/unix/sysv/linux/nanosleep_nocancel.c: ...this new file.
	* sysdeps/unix/sysv/linux/open.c: Move __open_nocancel to...
	* sysdeps/unix/sysv/linux/open_nocancel.c: ...this new file.
	* sysdeps/unix/sysv/linux/open64.c: Move __open64_nocancel to...
	* sysdeps/unix/sysv/linux/open64_nocancel.c: ...this new file.
	* sysdeps/unix/sysv/linux/openat.c: Move __openat_nocancel to...
	* sysdeps/unix/sysv/linux/openat_nocancel.c: ...this new file.
	* sysdeps/unix/sysv/linux/openat64.c: Move __openat64_nocancel to...
	* sysdeps/unix/sysv/linux/openat64_nocancel.c: ...this new file.
	* sysdeps/unix/sysv/linux/pause.c: Move __pause_nocancel to...
	* sysdeps/unix/sysv/linux/pause_nocancel.c: ...this new file.
	* sysdeps/unix/sysv/linux/read.c: Move __read_nocancel to...
	* sysdeps/unix/sysv/linux/read_nocancel.c: ...this new file.
	* sysdeps/unix/sysv/linux/waitpid.c: Move __waitpid_nocancel to...
	* sysdeps/unix/sysv/linux/waitpid_nocancel.c: ...this new file.
	* sysdeps/unix/sysv/linux/write.c: Move __write_nocancel to...
	* sysdeps/unix/sysv/linux/write_nocancel.c: ...this new file.

        * sysdeps/unix/sysv/linux/nios2/Makefile: Don't override
        libpthread-routines.
        * sysdeps/unix/sysv/linux/nios2/pt-vfork.S: New file which
        defines nothing.

        * sysdeps/mach/hurd/dl-sysdep.c: Define __read instead of
        __libc_read, and __write instead of __libc_write.  Define
        __open64 in addition to __open.
This commit is contained in:
Zack Weinberg
2018-04-03 18:26:44 -04:00
parent 0221ce2a90
commit 329ea513b4
45 changed files with 647 additions and 279 deletions
Download Patch File Download Diff File Expand all files Collapse all files

35
elf/dl-load.c
View File

@ -44,7 +44,7 @@
#include <dl-unmap-segments.h>
#include <dl-machine-reject-phdr.h>
#include <dl-sysdep-open.h>
#include <not-cancel.h>
#include <endian.h>
#if BYTE_ORDER == BIG_ENDIAN
@ -776,7 +776,7 @@ lose (int code, int fd, const char *name, char *realname, struct link_map *l,
{
/* The file might already be closed. */
if (fd != -1)
(void) __close (fd);
(void) __close_nocancel (fd);
if (l != NULL && l->l_origin != (char *) -1l)
free ((char *) l->l_origin);
free (l);
@ -835,7 +835,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
{
/* The object is already loaded.
Just bump its reference count and return it. */
__close (fd);
__close_nocancel (fd);
/* If the name is not in the list of names for this object add
it. */
@ -863,7 +863,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
/* No need to bump the refcount of the real object, ld.so will
never be unloaded. */
__close (fd);
__close_nocancel (fd);
/* Add the map for the mirrored object to the object list. */
_dl_add_to_namespace_list (l, nsid);
@ -877,7 +877,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
/* We are not supposed to load the object unless it is already
loaded. So return now. */
free (realname);
__close (fd);
__close_nocancel (fd);
return NULL;
}
@ -896,7 +896,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
if (_dl_zerofd == -1)
{
free (realname);
__close (fd);
__close_nocancel (fd);
_dl_signal_error (errno, NULL, NULL,
N_("cannot open zero fill device"));
}
@ -962,7 +962,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
{
phdr = alloca (maplength);
__lseek (fd, header->e_phoff, SEEK_SET);
if ((size_t) __libc_read (fd, (void *) phdr, maplength) != maplength)
if ((size_t) __read_nocancel (fd, (void *) phdr, maplength) != maplength)
{
errstring = N_("cannot read file data");
goto call_lose_errno;
@ -1232,7 +1232,7 @@ cannot enable executable stack as shared object requires");
l->l_tls_initimage = (char *) l->l_tls_initimage + l->l_addr;
/* We are done mapping in the file. We no longer need the descriptor. */
if (__glibc_unlikely (__close (fd) != 0))
if (__glibc_unlikely (__close_nocancel (fd) != 0))
{
errstring = N_("cannot close file descriptor");
goto call_lose_errno;
@ -1447,7 +1447,7 @@ open_verify (const char *name, int fd,
{
/* An audit library changed what we're supposed to open,
so FD no longer matches it. */
__close (fd);
__close_nocancel (fd);
fd = -1;
}
}
@ -1455,7 +1455,7 @@ open_verify (const char *name, int fd,
if (fd == -1)
/* Open the file. We always open files read-only. */
fd = __open (name, O_RDONLY | O_CLOEXEC);
fd = __open64_nocancel (name, O_RDONLY | O_CLOEXEC);
if (fd != -1)
{
@ -1474,8 +1474,8 @@ open_verify (const char *name, int fd,
/* Read in the header. */
do
{
ssize_t retlen = __libc_read (fd, fbp->buf + fbp->len,
sizeof (fbp->buf) - fbp->len);
ssize_t retlen = __read_nocancel (fd, fbp->buf + fbp->len,
sizeof (fbp->buf) - fbp->len);
if (retlen <= 0)
break;
fbp->len += retlen;
@ -1598,7 +1598,8 @@ open_verify (const char *name, int fd,
{
phdr = alloca (maplength);
__lseek (fd, ehdr->e_phoff, SEEK_SET);
if ((size_t) __libc_read (fd, (void *) phdr, maplength) != maplength)
if ((size_t) __read_nocancel (fd, (void *) phdr, maplength)
!= maplength)
{
read_error:
errval = errno;
@ -1648,7 +1649,7 @@ open_verify (const char *name, int fd,
abi_note = abi_note_malloced;
}
__lseek (fd, ph->p_offset, SEEK_SET);
if (__libc_read (fd, (void *) abi_note, size) != size)
if (__read_nocancel (fd, (void *) abi_note, size) != size)
{
free (abi_note_malloced);
goto read_error;
@ -1680,7 +1681,7 @@ open_verify (const char *name, int fd,
|| (GLRO(dl_osversion) && GLRO(dl_osversion) < osversion))
{
close_and_out:
__close (fd);
__close_nocancel (fd);
__set_errno (ENOENT);
fd = -1;
}
@ -1797,7 +1798,7 @@ open_path (const char *name, size_t namelen, int mode,
/* The shared object cannot be tested for being SUID
or this bit is not set. In this case we must not
use this object. */
__close (fd);
__close_nocancel (fd);
fd = -1;
/* We simply ignore the file, signal this by setting
the error value which would have been set by `open'. */
@ -1818,7 +1819,7 @@ open_path (const char *name, size_t namelen, int mode,
{
/* No memory for the name, we certainly won't be able
to load and link it. */
__close (fd);
__close_nocancel (fd);
return -1;
}
}