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Eric Biggers 2bc40caa80 fscrypt: add fscrypt_symlink_getattr() for computing st_size 
commit d187605605 upstream.

Add a helper function fscrypt_symlink_getattr() which will be called
from the various filesystems' ->getattr() methods to read and decrypt
the target of encrypted symlinks in order to report the correct st_size.

Detailed explanation:

As required by POSIX and as documented in various man pages, st_size for
a symlink is supposed to be the length of the symlink target.
Unfortunately, st_size has always been wrong for encrypted symlinks
because st_size is populated from i_size from disk, which intentionally
contains the length of the encrypted symlink target.  That's slightly
greater than the length of the decrypted symlink target (which is the
symlink target that userspace usually sees), and usually won't match the
length of the no-key encoded symlink target either.

This hadn't been fixed yet because reporting the correct st_size would
require reading the symlink target from disk and decrypting or encoding
it, which historically has been considered too heavyweight to do in
->getattr().  Also historically, the wrong st_size had only broken a
test (LTP lstat03) and there were no known complaints from real users.
(This is probably because the st_size of symlinks isn't used too often,
and when it is, typically it's for a hint for what buffer size to pass
to readlink() -- which a slightly-too-large size still works for.)

However, a couple things have changed now.  First, there have recently
been complaints about the current behavior from real users:

- Breakage in rpmbuild:
  https://github.com/rpm-software-management/rpm/issues/1682
  https://github.com/google/fscrypt/issues/305

- Breakage in toybox cpio:
  https://www.mail-archive.com/toybox@lists.landley.net/msg07193.html

- Breakage in libgit2: https://issuetracker.google.com/issues/189629152
  (on Android public issue tracker, requires login)

Second, we now cache decrypted symlink targets in ->i_link.  Therefore,
taking the performance hit of reading and decrypting the symlink target
in ->getattr() wouldn't be as big a deal as it used to be, since usually
it will just save having to do the same thing later.

Also note that eCryptfs ended up having to read and decrypt symlink
targets in ->getattr() as well, to fix this same issue; see
commit 3a60a1686f ("eCryptfs: Decrypt symlink target for stat size").

So, let's just bite the bullet, and read and decrypt the symlink target
in ->getattr() in order to report the correct st_size.  Add a function
fscrypt_symlink_getattr() which the filesystems will call to do this.

(Alternatively, we could store the decrypted size of symlinks on-disk.
But there isn't a great place to do so, and encryption is meant to hide
the original size to some extent; that property would be lost.)

Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210702065350.209646-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2021-09-03 10:23:06 +02:00
arch arm64: dts: qcom: msm8994-angler: Fix gpio-reserved-ranges 85-88 2021-09-03 10:23:06 +02:00
block blk-mq: don't grab rq's refcount in blk_mq_check_expired() 2021-09-03 10:23:03 +02:00
certs Kbuild updates for v5.13 (2nd) 2021-05-08 10:00:11 -07:00
crypto crypto: sm2 - fix a memory leak in sm2 2021-07-14 17:06:44 +02:00
Documentation dt-bindings: sifive-l2-cache: Fix 'select' matching 2021-09-03 10:22:47 +02:00
drivers Revert "floppy: reintroduce O_NDELAY fix" 2021-09-03 10:23:06 +02:00
fs fscrypt: add fscrypt_symlink_getattr() for computing st_size 2021-09-03 10:23:06 +02:00
include fscrypt: add fscrypt_symlink_getattr() for computing st_size 2021-09-03 10:23:06 +02:00
init sched/core: Initialize the idle task with preemption disabled 2021-07-14 17:06:21 +02:00
ipc ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry 2021-05-22 15:09:07 -10:00
kernel sched: Fix get_push_task() vs migrate_disable() 2021-09-03 10:22:59 +02:00
lib once: Fix panic when module unload 2021-09-03 10:22:46 +02:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
mm mm/memory_hotplug: fix potential permanent lru cache disable 2021-09-03 10:22:48 +02:00
net tipc: call tipc_wait_for_connect only when dlen is not 0 2021-09-03 10:23:05 +02:00
samples bpf, samples: Fix xdpsock with '-M' parameter missing unload process 2021-07-28 14:37:21 +02:00
scripts scripts/tracing: fix the bug that can't parse raw_trace_func 2021-08-12 13:32:16 +02:00
security bpf: Add lockdown check for probe_write_user helper 2021-08-15 14:01:56 +02:00
sound ASoC: component: Remove misplaced prefix handling in pin control functions 2021-09-03 10:22:44 +02:00
tools tools/virtio: fix build 2021-09-03 10:23:01 +02:00
usr .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
virt KVM: Do not leak memory for duplicate debugfs directories 2021-08-12 13:32:23 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Marek's other e-mail address and identity without diacritics 2021-06-24 19:40:54 -07:00
COPYING
CREDITS MAINTAINERS: move Murali Karicheri to credits 2021-04-29 15:47:30 -07:00
Kbuild
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Merge branch 'akpm' (patches from Andrew) 2021-06-25 11:05:03 -07:00
Makefile Linux 5.13.13 2021-08-26 08:48:43 -04:00
README

README

Linux kernel

There are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. Please read Documentation/admin-guide/README.rst first.

In order to build the documentation, use make htmldocs or make pdfdocs. The formatted documentation can also be read online at:

https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.