linux-stable.git/fs/readdir.c, branch v5.4.166

readdir: make sure to verify directory entry for legacy interfaces too

2021-04-21T10:56:16+00:00

commit 0c93ac69407d63a85be0129aa55ffaec27ffebd3 upstream.

This does the directory entry name verification for the legacy
"fillonedir" (and compat) interface that goes all the way back to the
dark ages before we had a proper dirent, and the readdir() system call
returned just a single entry at a time.

Nobody should use this interface unless you still have binaries from
1991, but let's do it right.

This came up during discussions about unsafe_copy_to_user() and proper
checking of all the inputs to it, as the networking layer is looking to
use it in a few new places. So let's make sure the _old_ users do it
all right and proper, before we add new ones.

See also commit 8a23eb804ca4 ("Make filldir[64]() verify the directory
entry filename is valid") which did the proper modern interfaces that
people actually use. It had a note:

Note that I didn't bother adding the checks to any legacy interfaces
that nobody uses.

which this now corrects. Note that we really don't care about POSIX and
the presense of '/' in a directory entry, but verify_dirent_name() also
ends up doing the proper name length verification which is what the
input checking discussion was about.

[ Another option would be to remove the support for this particular very
old interface: any binaries that use it are likely a.out binaries, and
they will no longer run anyway since we removed a.out binftm support
in commit eac616557050 ("x86: Deprecate a.out support").

But I'm not sure which came first: getdents() or ELF support, so let's
pretend somebody might still have a working binary that uses the
legacy readdir() case.. ]

Link: https://lore.kernel.org/lkml/CAHk-=wjbvzCAhAtvG0d81W5o0-KT5PPTHhfJ5ieDFq+bGtgOYg@mail.gmail.com/
Acked-by: Al Viro
Signed-off-by: Linus Torvalds
Signed-off-by: Greg Kroah-Hartman

readdir: be more conservative with directory entry names

2020-01-29T15:45:31+00:00

commit 2c6b7bcd747201441923a0d3062577a8d1fbd8f8 upstream.

Commit 8a23eb804ca4 ("Make filldir[64]() verify the directory entry
filename is valid") added some minimal validity checks on the directory
entries passed to filldir[64]().  But they really were pretty minimal.

This fleshes out at least the name length check: we used to disallow
zero-length names, but really, negative lengths or oevr-long names
aren't ok either.  Both could happen if there is some filesystem
corruption going on.

Now, most filesystems tend to use just an "unsigned char" or similar for
the length of a directory entry name, so even with a corrupt filesystem
you should never see anything odd like that.  But since we then use the
name length to create the directory entry record length, let's make sure
it actually is half-way sensible.

Note how POSIX states that the size of a path component is limited by
NAME_MAX, but we actually use PATH_MAX for the check here.  That's
because while NAME_MAX is generally the correct maximum name length
(it's 255, for the same old "name length is usually just a byte on
disk"), there's nothing in the VFS layer that really cares.

So the real limitation at a VFS layer is the total pathname length you
can pass as a filename: PATH_MAX.

Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

readdir: make user_access_begin() use the real access range

2020-01-29T15:45:29+00:00

commit 3c2659bd1db81ed6a264a9fc6262d51667d655ad upstream.

In commit 9f79b78ef744 ("Convert filldir[64]() from __put_user() to
unsafe_put_user()") I changed filldir to not do individual __put_user()
accesses, but instead use unsafe_put_user() surrounded by the proper
user_access_begin/end() pair.

That make them enormously faster on modern x86, where the STAC/CLAC
games make individual user accesses fairly heavy-weight.

However, the user_access_begin() range was not really the exact right
one, since filldir() has the unfortunate problem that it needs to not
only fill out the new directory entry, it also needs to fix up the
previous one to contain the proper file offset.

It's unfortunate, but the "d_off" field in "struct dirent" is _not_ the
file offset of the directory entry itself - it's the offset of the next
one.  So we end up backfilling the offset in the previous entry as we
walk along.

But since x86 didn't really care about the exact range, and used to be
the only architecture that did anything fancy in user_access_begin() to
begin with, the filldir[64]() changes did something lazy, and even
commented on it:

	/*
	 * Note! This range-checks 'previous' (which may be NULL).
	 * The real range was checked in getdents
	 */
	if (!user_access_begin(dirent, sizeof(*dirent)))
		goto efault;

and it all worked fine.

But now 32-bit ppc is starting to also implement user_access_begin(),
and the fact that we faked the range to only be the (possibly not even
valid) previous directory entry becomes a problem, because ppc32 will
actually be using the range that is passed in for more than just "check
that it's user space".

This is a complete rewrite of Christophe's original patch.

By saving off the record length of the previous entry instead of a
pointer to it in the filldir data structures, we can simplify the range
check and the writing of the previous entry d_off field.  No need for
any conditionals in the user accesses themselves, although we retain the
conditional EINTR checking for the "was this the first directory entry"
signal handling latency logic.

Fixes: 9f79b78ef744 ("Convert filldir[64]() from __put_user() to unsafe_put_user()")
Link: https://lore.kernel.org/lkml/a02d3426f93f7eb04960a4d9140902d278cab0bb.1579697910.git.christophe.leroy@c-s.fr/
Link: https://lore.kernel.org/lkml/408c90c4068b00ea8f1c41cca45b84ec23d4946b.1579783936.git.christophe.leroy@c-s.fr/
Reported-and-tested-by: Christophe Leroy 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

filldir[64]: remove WARN_ON_ONCE() for bad directory entries

2019-10-18T22:41:16+00:00

This was always meant to be a temporary thing, just for testing and to
see if it actually ever triggered.

The only thing that reported it was syzbot doing disk image fuzzing, and
then that warning is expected.  So let's just remove it before -rc4,
because the extra sanity testing should probably go to -stable, but we
don't want the warning to do so.

Reported-by: syzbot+3031f712c7ad5dd4d926@syzkaller.appspotmail.com
Fixes: 8a23eb804ca4 ("Make filldir[64]() verify the directory entry filename is valid")
Signed-off-by: Linus Torvalds

uaccess: implement a proper unsafe_copy_to_user() and switch filldir over to it

2019-10-07T19:56:48+00:00

In commit 9f79b78ef744 ("Convert filldir[64]() from __put_user() to
unsafe_put_user()") I made filldir() use unsafe_put_user(), which
improves code generation on x86 enormously.

But because we didn't have a "unsafe_copy_to_user()", the dirent name
copy was also done by hand with unsafe_put_user() in a loop, and it
turns out that a lot of other architectures didn't like that, because
unlike x86, they have various alignment issues.

Most non-x86 architectures trap and fix it up, and some (like xtensa)
will just fail unaligned put_user() accesses unconditionally.  Which
makes that "copy using put_user() in a loop" not work for them at all.

I could make that code do explicit alignment etc, but the architectures
that don't like unaligned accesses also don't really use the fancy
"user_access_begin/end()" model, so they might just use the regular old
__copy_to_user() interface.

So this commit takes that looping implementation, turns it into the x86
version of "unsafe_copy_to_user()", and makes other architectures
implement the unsafe copy version as __copy_to_user() (the same way they
do for the other unsafe_xyz() accessor functions).

Note that it only does this for the copying _to_ user space, and we
still don't have a unsafe version of copy_from_user().

That's partly because we have no current users of it, but also partly
because the copy_from_user() case is slightly different and cannot
efficiently be implemented in terms of a unsafe_get_user() loop (because
gcc can't do asm goto with outputs).

It would be trivial to do this using "rep movsb", which would work
really nicely on newer x86 cores, but really badly on some older ones.

Al Viro is looking at cleaning up all our user copy routines to make
this all a non-issue, but for now we have this simple-but-stupid version
for x86 that works fine for the dirent name copy case because those
names are short strings and we simply don't need anything fancier.

Fixes: 9f79b78ef744 ("Convert filldir[64]() from __put_user() to unsafe_put_user()")
Reported-by: Guenter Roeck 
Reported-and-tested-by: Tony Luck 
Cc: Al Viro 
Cc: Max Filippov 
Signed-off-by: Linus Torvalds

Make filldir[64]() verify the directory entry filename is valid

2019-10-05T19:00:36+00:00

This has been discussed several times, and now filesystem people are
talking about doing it individually at the filesystem layer, so head
that off at the pass and just do it in getdents{64}().

This is partially based on a patch by Jann Horn, but checks for NUL
bytes as well, and somewhat simplified.

There's also commentary about how it might be better if invalid names
due to filesystem corruption don't cause an immediate failure, but only
an error at the end of the readdir(), so that people can still see the
filenames that are ok.

There's also been discussion about just how much POSIX strictly speaking
requires this since it's about filesystem corruption.  It's really more
"protect user space from bad behavior" as pointed out by Jann.  But
since Eric Biederman looked up the POSIX wording, here it is for context:

 "From readdir:

   The readdir() function shall return a pointer to a structure
   representing the directory entry at the current position in the
   directory stream specified by the argument dirp, and position the
   directory stream at the next entry. It shall return a null pointer
   upon reaching the end of the directory stream. The structure dirent
   defined in the  header describes a directory entry.

  From definitions:

   3.129 Directory Entry (or Link)

   An object that associates a filename with a file. Several directory
   entries can associate names with the same file.

  ...

   3.169 Filename

   A name consisting of 1 to {NAME_MAX} bytes used to name a file. The
   characters composing the name may be selected from the set of all
   character values excluding the slash character and the null byte. The
   filenames dot and dot-dot have special meaning. A filename is
   sometimes referred to as a 'pathname component'."

Note that I didn't bother adding the checks to any legacy interfaces
that nobody uses.

Also note that if this ends up being noticeable as a performance
regression, we can fix that to do a much more optimized model that
checks for both NUL and '/' at the same time one word at a time.

We haven't really tended to optimize 'memchr()', and it only checks for
one pattern at a time anyway, and we really _should_ check for NUL too
(but see the comment about "soft errors" in the code about why it
currently only checks for '/')

See the CONFIG_DCACHE_WORD_ACCESS case of hash_name() for how the name
lookup code looks for pathname terminating characters in parallel.

Link: https://lore.kernel.org/lkml/20190118161440.220134-2-jannh@google.com/
Cc: Alexander Viro 
Cc: Jann Horn 
Cc: Eric W. Biederman 
Signed-off-by: Linus Torvalds

Convert filldir[64]() from __put_user() to unsafe_put_user()

2019-10-05T19:00:36+00:00

We really should avoid the "__{get,put}_user()" functions entirely,
because they can easily be mis-used and the original intent of being
used for simple direct user accesses no longer holds in a post-SMAP/PAN
world.

Manually optimizing away the user access range check makes no sense any
more, when the range check is generally much cheaper than the "enable
user accesses" code that the __{get,put}_user() functions still need.

So instead of __put_user(), use the unsafe_put_user() interface with
user_access_{begin,end}() that really does generate better code these
days, and which is generally a nicer interface.  Under some loads, the
multiple user writes that filldir() does are actually quite noticeable.

This also makes the dirent name copy use unsafe_put_user() with a couple
of macros.  We do not want to make function calls with SMAP/PAN
disabled, and the code this generates is quite good when the
architecture uses "asm goto" for unsafe_put_user() like x86 does.

Note that this doesn't bother with the legacy cases.  Nobody should use
them anyway, so performance doesn't really matter there.

Signed-off-by: Linus Torvalds

Remove 'type' argument from access_ok() function

2019-01-04T02:57:57+00:00

Nobody has actually used the type (VERIFY_READ vs VERIFY_WRITE) argument
of the user address range verification function since we got rid of the
old racy i386-only code to walk page tables by hand.

It existed because the original 80386 would not honor the write protect
bit when in kernel mode, so you had to do COW by hand before doing any
user access.  But we haven't supported that in a long time, and these
days the 'type' argument is a purely historical artifact.

A discussion about extending 'user_access_begin()' to do the range
checking resulted this patch, because there is no way we're going to
move the old VERIFY_xyz interface to that model.  And it's best done at
the end of the merge window when I've done most of my merges, so let's
just get this done once and for all.

This patch was mostly done with a sed-script, with manual fix-ups for
the cases that weren't of the trivial 'access_ok(VERIFY_xyz' form.

There were a couple of notable cases:

 - csky still had the old "verify_area()" name as an alias.

 - the iter_iov code had magical hardcoded knowledge of the actual
   values of VERIFY_{READ,WRITE} (not that they mattered, since nothing
   really used it)

 - microblaze used the type argument for a debug printout

but other than those oddities this should be a total no-op patch.

I tried to fix up all architectures, did fairly extensive grepping for
access_ok() uses, and the changes are trivial, but I may have missed
something.  Any missed conversion should be trivially fixable, though.

Signed-off-by: Linus Torvalds

fs: add ksys_getdents64() helper; remove in-kernel calls to sys_getdents64()

2018-04-02T18:16:02+00:00

Using this helper allows us to avoid the in-kernel calls to the
sys_getdents64() syscall. The ksys_ prefix denotes that this function
is meant as a drop-in replacement for the syscall. In particular, it
uses the same calling convention as sys_getdents64().

This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net

Cc: Alexander Viro 
Signed-off-by: Dominik Brodowski

Merge branch 'linus' into locking/core, to resolve conflicts

2017-11-07T09:32:44+00:00

Conflicts:
	include/linux/compiler-clang.h
	include/linux/compiler-gcc.h
	include/linux/compiler-intel.h
	include/uapi/linux/stddef.h

Signed-off-by: Ingo Molnar