Overlapping domain attachments using the current longest left exact
match fail in some simple cases, and with the fix to ensure consistent
behavior by failing unresolvable attachments it becomes important to
do a better job.
eg. under the current match the following are unresolvable where
the alternation is clearly a better match under the most specific
left match rule.
/**
/{bin/,}usr/
Use a counting match that detects when a loop in the state machine is
enter, and return the match count to provide a better specific left
match resolution.
Signed-off-by: John Johansen <john.johansen@canonical.com>
State differential encoding can provide better compression for
apparmor policy, without having significant impact on match time.
Signed-off-by: John Johansen <john.johansen@canonical.com>
The current split scheme is actually wrong in that it splits
///&
where that is invalid and should fail. Use the dfa to do a proper
bounded split without having to worry about getting the string
processing right in code.
Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Seth Arnold <seth.arnold@canonical.com>
Instead of testing whether a given dfa exists in every code path, have
a default null dfa that is used when loaded policy doesn't provide a
dfa.
This will let us get rid of special casing and avoid dereference bugs
when special casing is missed.
Signed-off-by: John Johansen <john.johansen@canonical.com>
The dfa is currently setup to be shared (has the basis of refcounting)
but currently can't be because the count can't be increased.
Signed-off-by: John Johansen <john.johansen@canonical.com>
Update aa_dfa_match so that it doesn't result in an input string being
walked twice (once to get its length and another time to match)
Add a single step functions
aa_dfa_next
Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Kees Cook <kees@ubuntu.com>
Remove kobject.h from files which don't need it, notably,
sched.h and fs.h.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
A basic dfa matching engine based off the dfa engine in the Dragon
Book. It uses simple row comb compression with a check field.
This allows AppArmor to do pattern matching in linear time, and also
avoids stack issues that an nfa based engine may have. The dfa
engine uses a byte based comparison, with all values being valid.
Any potential character encoding are handled user side when the dfa
tables are created. By convention AppArmor uses \0 to separate two
dependent path matches since \0 is not a valid path character
(this is done in the link permission check).
The dfa tables are generated in user space and are verified at load
time to be internally consistent.
There are several future improvements planned for the dfa engine:
* The dfa engine may be converted to a hybrid nfa-dfa engine, with
a fixed size limited stack. This would allow for size time
tradeoffs, by inserting limited nfa states to help control
state explosion that can occur with dfas.
* The dfa engine may pickup the ability to do limited dynamic
variable matching, instead of fixing all variables at policy
load time.
Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: James Morris <jmorris@namei.org>
John Johansen
Linus Torvalds
Alexey Dobriyan
Uwe Kleine-König