kernel/git/stable/linux-stable.git/fs/fcntl.c, branch linux-3.16.y

fcntl: Don't use ambiguous SIG_POLL si_codes

2017-11-26T13:50:14+00:00

commit d08477aa975e97f1dc64c0ae59cebf98520456ce upstream. We have a weird and problematic intersection of features that when they all come together result in ambiguous siginfo values, that we can not support properly. - Supporting fcntl(F_SETSIG,...) with arbitrary valid signals. - Using positive values for POLL_IN, POLL_OUT, POLL_MSG, ..., etc that imply they are signal specific si_codes and using the aforementioned arbitrary signal to deliver them. - Supporting injection of arbitrary siginfo values for debugging and checkpoint/restore. The result is that just looking at siginfo si_codes of 1 to 6 are ambigious. It could either be a signal specific si_code or it could be a generic si_code. For most of the kernel this is a non-issue but for sending signals with siginfo it is impossible to play back the kernel signals and get the same result. Strictly speaking when the si_code was changed from SI_SIGIO to POLL_IN and friends between 2.2 and 2.4 this functionality was not ambiguous, as only real time signals were supported. Before 2.4 was released the kernel began supporting siginfo with non realtime signals so they could give details of why the signal was sent. The result is that if F_SETSIG is set to one of the signals with signal specific si_codes then user space can not know why the signal was sent. I grepped through a bunch of userspace programs using debian code search to get a feel for how often people choose a signal that results in an ambiguous si_code. I only found one program doing so and it was using SIGCHLD to test the F_SETSIG functionality, and did not appear to be a real world usage. Therefore the ambiguity does not appears to be a real world problem in practice. Remove the ambiguity while introducing the smallest chance of breakage by changing the si_code to SI_SIGIO when signals with signal specific si_codes are targeted. Fixes: v2.3.40 -- Added support for queueing non-rt signals Fixes: v2.3.21 -- Changed the si_code from SI_SIGIO Signed-off-by: "Eric W. Biederman" Signed-off-by: Ben Hutchings

locks: rename file-private locks to "open file description locks"

2014-04-22T12:23:58+00:00

File-private locks have been merged into Linux for v3.15, and *now* people are commenting that the name and macro definitions for the new file-private locks suck. ...and I can't even disagree. The names and command macros do suck. We're going to have to live with these for a long time, so it's important that we be happy with the names before we're stuck with them. The consensus on the lists so far is that they should be rechristened as "open file description locks". The name isn't a big deal for the kernel, but the command macros are not visually distinct enough from the traditional POSIX lock macros. The glibc and documentation folks are recommending that we change them to look like F_OFD_{GETLK|SETLK|SETLKW}. That lessens the chance that a programmer will typo one of the commands wrong, and also makes it easier to spot this difference when reading code. This patch makes the following changes that I think are necessary before v3.15 ships: 1) rename the command macros to their new names. These end up in the uapi headers and so are part of the external-facing API. It turns out that glibc doesn't actually use the fcntl.h uapi header, but it's hard to be sure that something else won't. Changing it now is safest. 2) make the the /proc/locks output display these as type "OFDLCK" Cc: Michael Kerrisk Cc: Christoph Hellwig Cc: Carlos O'Donell Cc: Stefan Metzmacher Cc: Andy Lutomirski Cc: Frank Filz Cc: Theodore Ts'o Signed-off-by: Jeff Layton

locks: add new fcntl cmd values for handling file private locks

2014-03-31T12:24:43+00:00

Due to some unfortunate history, POSIX locks have very strange and unhelpful semantics. The thing that usually catches people by surprise is that they are dropped whenever the process closes any file descriptor associated with the inode. This is extremely problematic for people developing file servers that need to implement byte-range locks. Developers often need a "lock management" facility to ensure that file descriptors are not closed until all of the locks associated with the inode are finished. Additionally, "classic" POSIX locks are owned by the process. Locks taken between threads within the same process won't conflict with one another, which renders them useless for synchronization between threads. This patchset adds a new type of lock that attempts to address these issues. These locks conflict with classic POSIX read/write locks, but have semantics that are more like BSD locks with respect to inheritance and behavior on close. This is implemented primarily by changing how fl_owner field is set for these locks. Instead of having them owned by the files_struct of the process, they are instead owned by the filp on which they were acquired. Thus, they are inherited across fork() and are only released when the last reference to a filp is put. These new semantics prevent them from being merged with classic POSIX locks, even if they are acquired by the same process. These locks will also conflict with classic POSIX locks even if they are acquired by the same process or on the same file descriptor. The new locks are managed using a new set of cmd values to the fcntl() syscall. The initial implementation of this converts these values to "classic" cmd values at a fairly high level, and the details are not exposed to the underlying filesystem. We may eventually want to push this handing out to the lower filesystem code but for now I don't see any need for it. Also, note that with this implementation the new cmd values are only available via fcntl64() on 32-bit arches. There's little need to add support for legacy apps on a new interface like this. Signed-off-by: Jeff Layton

locks: pass the cmd value to fcntl_getlk/getlk64

2014-03-31T12:24:43+00:00

Once we introduce file private locks, we'll need to know what cmd value was used, as that affects the ownership and whether a conflict would arise. Signed-off-by: Jeff Layton

file->f_op is never NULL...

2013-10-25T03:34:54+00:00

Signed-off-by: Al Viro

vfs: add missing check for __O_TMPFILE in fcntl_init()

2013-08-05T14:25:32+00:00

As comment in include/uapi/asm-generic/fcntl.h described, when introducing new O_* bits, we need to check its uniqueness in fcntl_init(). But __O_TMPFILE bit is missing. So fix it. Signed-off-by: Zheng Liu Signed-off-by: Al Viro

new helper: file_inode(file)

2013-02-23T04:31:31+00:00

Signed-off-by: Al Viro

Fix F_DUPFD_CLOEXEC breakage

2012-10-09T06:52:31+00:00

Fix a braino in F_DUPFD_CLOEXEC; f_dupfd() expects flags for alloc_fd(), get_unused_fd() etc and there clone-on-exec if O_CLOEXEC, not FD_CLOEXEC. Reported-by: Richard W.M. Jones Signed-off-by: Al Viro Signed-off-by: Linus Torvalds

fcntl: fix misannotations

2012-09-27T02:20:20+00:00

__user * != * __user... Signed-off-by: Al Viro

switch simple cases of fget_light to fdget

2012-09-27T02:20:08+00:00

Signed-off-by: Al Viro