Translating a context struct to string can be quite slow, especially if
the context has a lot of category bits set. This can cause quite
noticeable performance impact in situations where the translation needs
to be done repeatedly. A common example is a UNIX datagram socket with
the SO_PASSSEC option enabled, which is used e.g. by systemd-journald
when receiving log messages via datagram socket. This scenario can be
reproduced with:
cat /dev/urandom | base64 | logger &
timeout 30s perf record -p $(pidof systemd-journald) -a -g
kill %1
perf report -g none --pretty raw | grep security_secid_to_secctx
Before the caching introduced by this patch, computing the context
string (security_secid_to_secctx() function) takes up ~65% of
systemd-journald's CPU time (assuming a context with 1024 categories
set and Fedora x86_64 release kernel configs). After this patch
(assuming near-perfect cache hit ratio) this overhead is reduced to just
~2%.
This patch addresses the issue by caching a certain number (compile-time
configurable) of recently used context strings to speed up repeated
translations of the same context, while using only a small amount of
memory.
The cache is integrated into the existing sidtab table by adding a field
to each entry, which when not NULL contains an RCU-protected pointer to
a cache entry containing the cached string. The cache entries are kept
in a linked list sorted according to how recently they were used. On a
cache miss when the cache is full, the least recently used entry is
removed to make space for the new entry.
The patch migrates security_sid_to_context_core() to use the cache (also
a few other functions where it was possible without too much fuss, but
these mostly use the translation for logging in case of error, which is
rare).
Link: https://bugzilla.redhat.com/show_bug.cgi?id=1733259
Cc: Michal Sekletar <msekleta@redhat.com>
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Reviewed-by: Stephen Smalley <sds@tycho.nsa.gov>
Tested-by: Stephen Smalley <sds@tycho.nsa.gov>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
[PM: lots of merge fixups due to collisions with other sidtab patches]
Signed-off-by: Paul Moore <paul@paul-moore.com>
This replaces the reverse table lookup and reverse cache with a
hashtable which improves cache-miss reverse-lookup times from
O(n) to O(1)* and maintains the same performance as a reverse
cache hit.
This reduces the time needed to add a new sidtab entry from ~500us
to 5us on a Pixel 3 when there are ~10,000 sidtab entries.
The implementation uses the kernel's generic hashtable API,
It uses the context's string represtation as the hash source,
and the kernels generic string hashing algorithm full_name_hash()
to reduce the string to a 32 bit value.
This change also maintains the improvement introduced in
commit ee1a84fdfe ("selinux: overhaul sidtab to fix bug and improve
performance") which removed the need to keep the current sidtab
locked during policy reload. It does however introduce periodic
locking of the target sidtab while converting the hashtable. Sidtab
entries are never modified or removed, so the context struct stored
in the sid_to_context tree can also be used for the context_to_sid
hashtable to reduce memory usage.
This bug was reported by:
- On the selinux bug tracker.
BUG: kernel softlockup due to too many SIDs/contexts #37https://github.com/SELinuxProject/selinux-kernel/issues/37
- Jovana Knezevic on Android's bugtracker.
Bug: 140252993
"During multi-user performance testing, we create and remove users
many times. selinux_android_restorecon_pkgdir goes from 1ms to over
20ms after about 200 user creations and removals. Accumulated over
~280 packages, that adds a significant time to user creation,
making perf benchmarks unreliable."
* Hashtable lookup is only O(1) when n < the number of buckets.
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Reported-by: Stephen Smalley <sds@tycho.nsa.gov>
Reported-by: Jovana Knezevic <jovanak@google.com>
Reviewed-by: Stephen Smalley <sds@tycho.nsa.gov>
Tested-by: Stephen Smalley <sds@tycho.nsa.gov>
[PM: subj tweak, removed changelog from patch description]
Signed-off-by: Paul Moore <paul@paul-moore.com>
As noted in Documentation/atomic_t.txt, if we don't need the RMW atomic
operations, we should only use READ_ONCE()/WRITE_ONCE() +
smp_rmb()/smp_wmb() where necessary (or the combined variants
smp_load_acquire()/smp_store_release()).
This patch converts the sidtab code to use regular u32 for the counter
and reverse lookup cache and use the appropriate operations instead of
atomic_get()/atomic_set(). Note that when reading/updating the reverse
lookup cache we don't need memory barriers as it doesn't need to be
consistent or accurate. We can now also replace some atomic ops with
regular loads (when under spinlock) and stores (for conversion target
fields that are always accessed under the master table's spinlock).
We can now also bump SIDTAB_MAX to U32_MAX as we can use the full u32
range again.
Suggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Reviewed-by: Jann Horn <jannh@google.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
We need to error out when trying to add an entry above SIDTAB_MAX in
sidtab_reverse_lookup() to avoid overflow on the odd chance that this
happens.
Cc: stable@vger.kernel.org
Fixes: ee1a84fdfe ("selinux: overhaul sidtab to fix bug and improve performance")
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Before this patch, during a policy reload the sidtab would become frozen
and trying to map a new context to SID would be unable to add a new
entry to sidtab and fail with -ENOMEM.
Such failures are usually propagated into userspace, which has no way of
distignuishing them from actual allocation failures and thus doesn't
handle them gracefully. Such situation can be triggered e.g. by the
following reproducer:
while true; do load_policy; echo -n .; sleep 0.1; done &
for (( i = 0; i < 1024; i++ )); do
runcon -l s0:c$i echo -n x || break
# or:
# chcon -l s0:c$i <some_file> || break
done
This patch overhauls the sidtab so it doesn't need to be frozen during
policy reload, thus solving the above problem.
The new SID table leverages the fact that SIDs are allocated
sequentially and are never invalidated and stores them in linear buckets
indexed by a tree structure. This brings several advantages:
1. Fast SID -> context lookup - this lookup can now be done in
logarithmic time complexity (usually in less than 4 array lookups)
and can still be done safely without locking.
2. No need to re-search the whole table on reverse lookup miss - after
acquiring the spinlock only the newly added entries need to be
searched, which means that reverse lookups that end up inserting a
new entry are now about twice as fast.
3. No need to freeze sidtab during policy reload - it is now possible
to handle insertion of new entries even during sidtab conversion.
The tree structure of the new sidtab is able to grow automatically to up
to about 2^31 entries (at which point it should not have more than about
4 tree levels). The old sidtab had a theoretical capacity of almost 2^32
entries, but half of that is still more than enough since by that point
the reverse table lookups would become unusably slow anyway...
The number of entries per tree node is selected automatically so that
each node fits into a single page, which should be the easiest size for
kmalloc() to handle.
Note that the cache for reverse lookup is preserved with equivalent
logic. The only difference is that instead of storing pointers to the
hash table nodes it stores just the indices of the cached entries.
The new cache ensures that the indices are loaded/stored atomically, but
it still has the drawback that concurrent cache updates may mess up the
contents of the cache. Such situation however only reduces its
effectivity, not the correctness of lookups.
Tested by selinux-testsuite and thoroughly tortured by this simple
stress test:
```
function rand_cat() {
echo $(( $RANDOM % 1024 ))
}
function do_work() {
while true; do
echo -n "system_u:system_r:kernel_t:s0:c$(rand_cat),c$(rand_cat)" \
>/sys/fs/selinux/context 2>/dev/null || true
done
}
do_work >/dev/null &
do_work >/dev/null &
do_work >/dev/null &
while load_policy; do echo -n .; sleep 0.1; done
kill %1
kill %2
kill %3
```
Link: https://github.com/SELinuxProject/selinux-kernel/issues/38
Reported-by: Orion Poplawski <orion@nwra.com>
Reported-by: Li Kun <hw.likun@huawei.com>
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Reviewed-by: Stephen Smalley <sds@tycho.nsa.gov>
[PM: most of sidtab.c merged by hand due to conflicts]
[PM: checkpatch fixes in mls.c, services.c, sidtab.c]
Signed-off-by: Paul Moore <paul@paul-moore.com>
This moves handling of initial SIDs into a separate table. Note that the
SIDs stored in the main table are now shifted by SECINITSID_NUM and
converted to/from the actual SIDs transparently by helper functions.
This change doesn't make much sense on its own, but it simplifies
further sidtab overhaul in a succeeding patch.
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Reviewed-by: Stephen Smalley <sds@tycho.nsa.gov>
[PM: fixed some checkpatch warnings on line length, whitespace]
Signed-off-by: Paul Moore <paul@paul-moore.com>
This is a purely cosmetic change that encapsulates the three-step sidtab
conversion logic (shutdown -> clone -> map) into a single function
defined in sidtab.c (as opposed to services.c).
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
[PM: whitespaces fixes to make checkpatch happy]
Signed-off-by: Paul Moore <paul@paul-moore.com>
Replace printk with pr_* to avoid checkpatch warnings.
Signed-off-by: Peter Enderborg <peter.enderborg@sony.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.
By default all files without license information are under the default
license of the kernel, which is GPL version 2.
Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier. The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.
This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.
How this work was done:
Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
- file had no licensing information it it.
- file was a */uapi/* one with no licensing information in it,
- file was a */uapi/* one with existing licensing information,
Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.
The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne. Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.
The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed. Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.
Criteria used to select files for SPDX license identifier tagging was:
- Files considered eligible had to be source code files.
- Make and config files were included as candidates if they contained >5
lines of source
- File already had some variant of a license header in it (even if <5
lines).
All documentation files were explicitly excluded.
The following heuristics were used to determine which SPDX license
identifiers to apply.
- when both scanners couldn't find any license traces, file was
considered to have no license information in it, and the top level
COPYING file license applied.
For non */uapi/* files that summary was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 11139
and resulted in the first patch in this series.
If that file was a */uapi/* path one, it was "GPL-2.0 WITH
Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 WITH Linux-syscall-note 930
and resulted in the second patch in this series.
- if a file had some form of licensing information in it, and was one
of the */uapi/* ones, it was denoted with the Linux-syscall-note if
any GPL family license was found in the file or had no licensing in
it (per prior point). Results summary:
SPDX license identifier # files
---------------------------------------------------|------
GPL-2.0 WITH Linux-syscall-note 270
GPL-2.0+ WITH Linux-syscall-note 169
((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21
((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17
LGPL-2.1+ WITH Linux-syscall-note 15
GPL-1.0+ WITH Linux-syscall-note 14
((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5
LGPL-2.0+ WITH Linux-syscall-note 4
LGPL-2.1 WITH Linux-syscall-note 3
((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3
((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1
and that resulted in the third patch in this series.
- when the two scanners agreed on the detected license(s), that became
the concluded license(s).
- when there was disagreement between the two scanners (one detected a
license but the other didn't, or they both detected different
licenses) a manual inspection of the file occurred.
- In most cases a manual inspection of the information in the file
resulted in a clear resolution of the license that should apply (and
which scanner probably needed to revisit its heuristics).
- When it was not immediately clear, the license identifier was
confirmed with lawyers working with the Linux Foundation.
- If there was any question as to the appropriate license identifier,
the file was flagged for further research and to be revisited later
in time.
In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.
Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights. The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.
Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.
In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.
Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
- a full scancode scan run, collecting the matched texts, detected
license ids and scores
- reviewing anything where there was a license detected (about 500+
files) to ensure that the applied SPDX license was correct
- reviewing anything where there was no detection but the patch license
was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
SPDX license was correct
This produced a worksheet with 20 files needing minor correction. This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.
These .csv files were then reviewed by Greg. Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected. This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.) Finally Greg ran the script using the .csv files to
generate the patches.
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Update my email address since epoch.ncsc.mil no longer exists.
MAINTAINERS and CREDITS are already correct.
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>
* Return an error code without storing it in an intermediate variable.
* Delete the local variable "rc" and the jump label "out" which became
unnecessary with this refactoring.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Paul Moore <paul@paul-moore.com>
The script "checkpatch.pl" pointed information out like the following.
Comparison to NULL could be written !…
Thus fix affected source code places.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Paul Moore <paul@paul-moore.com>
A multiplication for the size determination of a memory allocation
indicated that an array data structure should be processed.
Thus use the corresponding function "kmalloc_array".
This issue was detected by using the Coccinelle software.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Paul Moore <paul@paul-moore.com>
sidtab_context_to_sid takes up a large share of time when creating large
numbers of new inodes (~30-40% in oprofile runs). This patch implements a
cache of 3 entries which is checked before we do a full context_to_sid lookup.
On one system this showed over a x3 improvement in the number of inodes that
could be created per second and around a 20% improvement on another system.
Any time we look up the same context string sucessivly (imagine ls -lZ) we
should hit this cache hot. A cache miss should have a relatively minor affect
on performance next to doing the full table search.
All operations on the cache are done COMPLETELY lockless. We know that all
struct sidtab_node objects created will never be deleted until a new policy is
loaded thus we never have to worry about a pointer being dereferenced. Since
we also know that pointer assignment is atomic we know that the cache will
always have valid pointers. Given this information we implement a FIFO cache
in an array of 3 pointers. Every result (whether a cache hit or table lookup)
will be places in the 0 spot of the cache and the rest of the entries moved
down one spot. The 3rd entry will be lost.
Races are possible and are even likely to happen. Lets assume that 4 tasks
are hitting sidtab_context_to_sid. The first task checks against the first
entry in the cache and it is a miss. Now lets assume a second task updates
the cache with a new entry. This will push the first entry back to the second
spot. Now the first task might check against the second entry (which it
already checked) and will miss again. Now say some third task updates the
cache and push the second entry to the third spot. The first task my check
the third entry (for the third time!) and again have a miss. At which point
it will just do a full table lookup. No big deal!
Signed-off-by: Eric Paris <eparis@redhat.com>
Replace "thing != NULL" comparisons with just "thing" to make
the code look more uniform (mixed styles were used even in the
same source file).
Signed-off-by: Vesa-Matti Kari <vmkari@cc.helsinki.fi>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>
Introduce SELinux support for deferred mapping of security contexts in
the SID table upon policy reload, and use this support for inode
security contexts when the context is not yet valid under the current
policy. Only processes with CAP_MAC_ADMIN + mac_admin permission in
policy can set undefined security contexts on inodes. Inodes with
such undefined contexts are treated as having the unlabeled context
until the context becomes valid upon a policy reload that defines the
context. Context invalidation upon policy reload also uses this
support to save the context information in the SID table and later
recover it upon a subsequent policy reload that defines the context
again.
This support is to enable package managers and similar programs to set
down file contexts unknown to the system policy at the time the file
is created in order to better support placing loadable policy modules
in packages and to support build systems that need to create images of
different distro releases with different policies w/o requiring all of
the contexts to be defined or legal in the build host policy.
With this patch applied, the following sequence is possible, although
in practice it is recommended that this permission only be allowed to
specific program domains such as the package manager.
# rmdir baz
# rm bar
# touch bar
# chcon -t foo_exec_t bar # foo_exec_t is not yet defined
chcon: failed to change context of `bar' to `system_u:object_r:foo_exec_t': Invalid argument
# mkdir -Z system_u:object_r:foo_exec_t baz
mkdir: failed to set default file creation context to `system_u:object_r:foo_exec_t': Invalid argument
# cat setundefined.te
policy_module(setundefined, 1.0)
require {
type unconfined_t;
type unlabeled_t;
}
files_type(unlabeled_t)
allow unconfined_t self:capability2 mac_admin;
# make -f /usr/share/selinux/devel/Makefile setundefined.pp
# semodule -i setundefined.pp
# chcon -t foo_exec_t bar # foo_exec_t is not yet defined
# mkdir -Z system_u:object_r:foo_exec_t baz
# ls -Zd bar baz
-rw-r--r-- root root system_u:object_r:unlabeled_t bar
drwxr-xr-x root root system_u:object_r:unlabeled_t baz
# cat foo.te
policy_module(foo, 1.0)
type foo_exec_t;
files_type(foo_exec_t)
# make -f /usr/share/selinux/devel/Makefile foo.pp
# semodule -i foo.pp # defines foo_exec_t
# ls -Zd bar baz
-rw-r--r-- root root user_u:object_r:foo_exec_t bar
drwxr-xr-x root root system_u:object_r:foo_exec_t baz
# semodule -r foo
# ls -Zd bar baz
-rw-r--r-- root root system_u:object_r:unlabeled_t bar
drwxr-xr-x root root system_u:object_r:unlabeled_t baz
# semodule -i foo.pp
# ls -Zd bar baz
-rw-r--r-- root root user_u:object_r:foo_exec_t bar
drwxr-xr-x root root system_u:object_r:foo_exec_t baz
# semodule -r setundefined foo
# chcon -t foo_exec_t bar # no longer defined and not allowed
chcon: failed to change context of `bar' to `system_u:object_r:foo_exec_t': Invalid argument
# rmdir baz
# mkdir -Z system_u:object_r:foo_exec_t baz
mkdir: failed to set default file creation context to `system_u:object_r:foo_exec_t': Invalid argument
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>
This patch changes sidtab.c to fix whitespace and syntax issues. Things that
are fixed may include (does not not have to include)
whitespace at end of lines
spaces followed by tabs
spaces used instead of tabs
spacing around parenthesis
locateion of { around struct and else clauses
location of * in pointer declarations
removal of initialization of static data to keep it in the right section
useless {} in if statemetns
useless checking for NULL before kfree
fixing of the indentation depth of switch statements
and any number of other things I forgot to mention
Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>
Below is a patch which demotes many printk lines to KERN_DEBUG from
KERN_INFO. It should help stop the spamming of logs with messages in
which users are not interested nor is there any action that users should
take. It also promotes some KERN_INFO to KERN_ERR such as when there
are improper attempts to register/unregister security modules.
A similar patch was discussed a while back on list:
http://marc.theaimsgroup.com/?t=116656343500003&r=1&w=2
This patch addresses almost all of the issues raised. I believe the
only advice not taken was in the demoting of messages related to
undefined permissions and classes.
Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
security/selinux/hooks.c | 20 ++++++++++----------
security/selinux/ss/avtab.c | 2 +-
security/selinux/ss/policydb.c | 6 +++---
security/selinux/ss/sidtab.c | 2 +-
4 files changed, 15 insertions(+), 15 deletions(-)
Signed-off-by: James Morris <jmorris@namei.org>
After Al Viro (finally) succeeded in removing the sched.h #include in module.h
recently, it makes sense again to remove other superfluous sched.h includes.
There are quite a lot of files which include it but don't actually need
anything defined in there. Presumably these includes were once needed for
macros that used to live in sched.h, but moved to other header files in the
course of cleaning it up.
To ease the pain, this time I did not fiddle with any header files and only
removed #includes from .c-files, which tend to cause less trouble.
Compile tested against 2.6.20-rc2 and 2.6.20-rc2-mm2 (with offsets) on alpha,
arm, i386, ia64, mips, powerpc, and x86_64 with allnoconfig, defconfig,
allmodconfig, and allyesconfig as well as a few randconfigs on x86_64 and all
configs in arch/arm/configs on arm. I also checked that no new warnings were
introduced by the patch (actually, some warnings are removed that were emitted
by unnecessarily included header files).
Signed-off-by: Tim Schmielau <tim@physik3.uni-rostock.de>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
