[PATCH v3 0/8] Getting rid of get_unused_fd() / use O_CLOEXEC

[PATCH v3 0/8] Getting rid of get_unused_fd() / use O_CLOEXEC

[Yann Droneaud]

Hi,

With help from subsystem maintainers, I've managed to get some of
get_unused_fd() calls converted to use get_unused_fd_flags(O_CLOEXEC)
instead. [ANDROID][IB][VFIO]

KVM subsystem maintainers helped me to change calls to anon_inode_getfd()
to use O_CLOEXEC by default. [KVM]

Some maintainers applied my patches to convert get_unused_fd() to
get_unused_fd_flags(0) were using O_CLOEXEC wasn't possible without breaking ABI.
[SCTP][XFS]

So, still in the hope to get rid of get_unused_fd(), please find a another
attempt to remove get_unused_fd() macro and encourage subsystems to use
get_unused_fd_flags(O_CLOEXEC) or anon_inode_getfd(O_CLOEXEC) by default
were appropriate.

The patchset convert all calls to get_unused_fd()
to get_unused_fd_flags(0) before removing get_unused_fd() macro.

Without get_unused_fd() macro, more subsystems are likely to use
anon_inode_getfd() and be teached to provide an API that let userspace
choose the opening flags of the file descriptor.

Additionally I'm suggesting Industrial IO (IIO) subsystem to use
anon_inode_getfd(O_CLOEXEC): it's the only subsystem using anon_inode_getfd()
with a fixed set of flags not including O_CLOEXEC.

Not using O_CLOEXEC by default or not letting userspace provide the "open" flags
should be considered bad practice from security point of view:
in most case O_CLOEXEC must be used to not leak file descriptor across exec().
Using O_CLOEXEC by default when flags are not provided by userspace allows it
to choose, without race, if the file descriptor is going to be inherited
across exec().

Status:

In linux-next tag 20130906, they're currently:

- 22 calls to get_unused_fd_flags()     (+3)
     not counting get_unused_fd() and anon_inode_getfd()
-  7 calls to get_unused_fd()           (-3)
- 11 calls to anon_inode_getfd()        (0)

Changes from patchset v2 [PATCHSETv2]:

- android/sw_sync: use get_unused_fd_flags(O_CLOEXEC) instead of get_unused_fd()
  DROPPED: applied upstream

- android/sync: use get_unused_fd_flags(O_CLOEXEC) instead of get_unused_fd()
  DROPPED: applied upstream

- vfio: use get_unused_fd_flags(0) instead of get_unused_fd()
  DROPPED: applied upstream.
  Additionally subsystem maintainer applied another patch on top
  to set the flags to O_CLOEXEC.

- industrialio: use anon_inode_getfd() with O_CLOEXEC flag
  NEW: propose to use O_CLOEXEC as default flag.

Links:

[ANDROID]
  http://lkml.kernel.org/r/CACSP8SjXGMk2_kX_+RgzqqQwqKernvF1Wt3K5tw991W5dfAnCA@mail.gmail.com
  http://lkml.kernel.org/r/CACSP8SjZcpcpEtQHzcGYhf-MP7QGo0XpN7-uN7rmD=vNtopG=w@mail.gmail.com

[IB]
  http://lkml.kernel.org/r/CAL1RGDXV1_BjSLrQDFdVQ1_D75+bMtOtikHOUp8VBiy_OJUf=w@mail.gmail.com

[VFIO]
  http://lkml.kernel.org/r/20130822171744.1297.13711.stgit@bling.home

[KVM]
  http://lkml.kernel.org/r/5219A8FC.8090307@redhat.com
  http://lkml.kernel.org/r/3557EF65-4327-4DAE-999A-B0EE13C433F5@suse.de
  http://lkml.kernel.org/r/20130826102023.GA8218@redhat.com

[SCTP]
  http://lkml.kernel.org/r/51D312E8.6090702@gmail.com
  http://lkml.kernel.org/r/20130702.161428.1703028286206350504.davem@davemloft.net

[XFS]
  http://lkml.kernel.org/r/20130709205321.GV20932@sgi.com

[PATCHSETv2]
  http://lkml.kernel.org/r/cover.1376327678.git.ydroneaud@opteya.com

Yann Droneaud (8):
  ia64: use get_unused_fd_flags(0) instead of get_unused_fd()
  ppc/cell: use get_unused_fd_flags(0) instead of get_unused_fd()
  binfmt_misc: use get_unused_fd_flags(0) instead of get_unused_fd()
  file: use get_unused_fd_flags(0) instead of get_unused_fd()
  fanotify: use get_unused_fd_flags(0) instead of get_unused_fd()
  events: use get_unused_fd_flags(0) instead of get_unused_fd()
  file: remove get_unused_fd()
  industrialio: use anon_inode_getfd() with O_CLOEXEC flag

 arch/ia64/kernel/perfmon.c                | 2 +-
 arch/powerpc/platforms/cell/spufs/inode.c | 4 ++--
 drivers/iio/industrialio-event.c          | 2 +-
 fs/binfmt_misc.c                          | 2 +-
 fs/file.c                                 | 2 +-
 fs/notify/fanotify/fanotify_user.c        | 2 +-
 include/linux/file.h                      | 1 -
 kernel/events/core.c                      | 2 +-
 8 files changed, 8 insertions(+), 9 deletions(-)

-- 
1.8.3.1

[PATCH v3 3/8] binfmt_misc: use get_unused_fd_flags(0) instead of get_unused_fd()

[Yann Droneaud]

Macro get_unused_fd() is used to allocate a file descriptor with
default flags. Those default flags (0) can be "unsafe":
O_CLOEXEC must be used by default to not leak file descriptor
across exec().

Instead of macro get_unused_fd(), functions anon_inode_getfd()
or get_unused_fd_flags() should be used with flags given by userspace.
If not possible, flags should be set to O_CLOEXEC to provide userspace
with a default safe behavor.

In a further patch, get_unused_fd() will be removed so that
new code start using anon_inode_getfd() or get_unused_fd_flags()
with correct flags.

This patch replaces calls to get_unused_fd() with equivalent call to
get_unused_fd_flags(0) to preserve current behavor for existing code.

The hard coded flag value (0) should be reviewed on a per-subsystem basis,
and, if possible, set to O_CLOEXEC.

Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Link: http://lkml.kernel.org/r/cover.1378460926.git.ydroneaud@opteya.com
---
 fs/binfmt_misc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index 1c740e1..052f6dc 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -138,7 +138,7 @@ static int load_misc_binary(struct linux_binprm *bprm)
 		/* if the binary should be opened on behalf of the
 		 * interpreter than keep it open and assign descriptor
 		 * to it */
- 		fd_binary = get_unused_fd();
+		fd_binary = get_unused_fd_flags(0);
  		if (fd_binary < 0) {
  			retval = fd_binary;
  			goto _ret;
-- 
1.8.3.1

[PATCH v3 4/8] file: use get_unused_fd_flags(0) instead of get_unused_fd()

[Yann Droneaud]

Macro get_unused_fd() is used to allocate a file descriptor with
default flags. Those default flags (0) can be "unsafe":
O_CLOEXEC must be used by default to not leak file descriptor
across exec().

Instead of macro get_unused_fd(), functions anon_inode_getfd()
or get_unused_fd_flags() should be used with flags given by userspace.
If not possible, flags should be set to O_CLOEXEC to provide userspace
with a default safe behavor.

In a further patch, get_unused_fd() will be removed so that
new code start using anon_inode_getfd() or get_unused_fd_flags()
with correct flags.

This patch replaces calls to get_unused_fd() with equivalent call to
get_unused_fd_flags(0) to preserve current behavor for existing code.

The hard coded flag value (0) should be reviewed on a per-subsystem basis,
and, if possible, set to O_CLOEXEC.

Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Link: http://lkml.kernel.org/r/cover.1378460926.git.ydroneaud@opteya.com
---
 fs/file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/file.c b/fs/file.c
index 4a78f98..1420d28 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -897,7 +897,7 @@ SYSCALL_DEFINE1(dup, unsigned int, fildes)
 	struct file *file = fget_raw(fildes);
 
 	if (file) {
-		ret = get_unused_fd();
+		ret = get_unused_fd_flags(0);
 		if (ret >= 0)
 			fd_install(ret, file);
 		else
-- 
1.8.3.1