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parser: Fix invalid reference to transitions when building the chfa

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States are not guaranteed to have transitions, but when inserting
a state into the chfa table there is an unconditional dereference
to the states first transition.

This will result in a bad reference and could result in an OOB
flag being set on the state when it shouldn't be.

Fixes: 16b67ddbd ("add ability to use out of band transitions"
Closes: https://gitlab.com/apparmor/apparmor/-/issues/290
Reported-by: Nobel Barakat <nobelbarakat@google.com>
Reported-by: Oleksandr Tymoshenko <ovt@google.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>
This commit is contained in:
John Johansen 2022-12-07 18:08:12 -08:00
parent 2bd9962611
commit 27d738c874
1 changed files with 11 additions and 3 deletions
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14
parser/libapparmor_re/chfa.cc
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@ -193,9 +193,8 @@ void CHFA::insert_state(vector<pair<size_t, size_t> > &free_list,
State *default_state = dfa.nonmatching;
ssize_t base = 0;
int resize;
StateTrans &trans = from->trans;
ssize_t c = trans.begin()->first.c;
ssize_t c;
ssize_t prev = 0;
ssize_t x = first_free;
@ -204,6 +203,7 @@ void CHFA::insert_state(vector<pair<size_t, size_t> > &free_list,
if (trans.empty())
goto do_insert;
c = trans.begin()->first.c;
repeat:
resize = 0;
/* get the first free entry that won't underflow */
@ -251,10 +251,18 @@ repeat:
first_free = next;
}
do_insert:
/* these flags will only be set on states that have transitions */
if (c < 0) {
base |= MATCH_FLAG_OOB_TRANSITION;
}
do_insert:
/* While a state without transitions could have the diff encode
* flag set, it would be pointless resulting in just an extra
* state transition in the encoding chain, and so it should be
* considered an error
* TODO: add check that state without transitions isn't being
* given a diffencode flag
*/
if (from->flags & DiffEncodeFlag)
base |= DiffEncodeBit32;
default_base.push_back(make_pair(default_state, base));