From 39440b137546a3aa383cfdabc605fb73811b6093 Mon Sep 17 00:00:00 2001 From: John Johansen Date: Fri, 17 Oct 2025 01:53:00 -0700 Subject: [PATCH] apparmor: fix differential encoding verification Differential encoding allows loops to be created if it is abused. To prevent this the unpack should verify that a diff-encode chain terminates. Unfortunately the differential encode verification had two bugs. 1. it conflated states that had gone through check and already been marked, with states that were currently being checked and marked. This means that loops in the current chain being verified are treated as a chain that has already been verified. 2. the order bailout on already checked states compared current chain check iterators j,k instead of using the outer loop iterator i. Meaning a step backwards in states in the current chain verification was being mistaken for moving to an already verified state. Move to a double mark scheme where already verified states get a different mark, than the current chain being kept. This enables us to also drop the backwards verification check that was the cause of the second error as any already verified state is already marked. Fixes: 031dcc8f4e84 ("apparmor: dfa add support for state differential encoding") Reported-by: Qualys Security Advisory Tested-by: Salvatore Bonaccorso Reviewed-by: Georgia Garcia Reviewed-by: Cengiz Can Signed-off-by: John Johansen --- security/apparmor/include/match.h | 1 + security/apparmor/match.c | 23 +++++++++++++++++++---- 2 files changed, 20 insertions(+), 4 deletions(-) diff --git a/security/apparmor/include/match.h b/security/apparmor/include/match.h index 0dde8eda3d1a..7accb1c39849 100644 --- a/security/apparmor/include/match.h +++ b/security/apparmor/include/match.h @@ -185,6 +185,7 @@ static inline void aa_put_dfa(struct aa_dfa *dfa) #define MATCH_FLAG_DIFF_ENCODE 0x80000000 #define MARK_DIFF_ENCODE 0x40000000 #define MATCH_FLAG_OOB_TRANSITION 0x20000000 +#define MARK_DIFF_ENCODE_VERIFIED 0x10000000 #define MATCH_FLAGS_MASK 0xff000000 #define MATCH_FLAGS_VALID (MATCH_FLAG_DIFF_ENCODE | MATCH_FLAG_OOB_TRANSITION) #define MATCH_FLAGS_INVALID (MATCH_FLAGS_MASK & ~MATCH_FLAGS_VALID) diff --git a/security/apparmor/match.c b/security/apparmor/match.c index 2aad2cbed565..e9fac67e5178 100644 --- a/security/apparmor/match.c +++ b/security/apparmor/match.c @@ -202,16 +202,31 @@ static int verify_dfa(struct aa_dfa *dfa) size_t j, k; for (j = i; - (BASE_TABLE(dfa)[j] & MATCH_FLAG_DIFF_ENCODE) && - !(BASE_TABLE(dfa)[j] & MARK_DIFF_ENCODE); + ((BASE_TABLE(dfa)[j] & MATCH_FLAG_DIFF_ENCODE) && + !(BASE_TABLE(dfa)[j] & MARK_DIFF_ENCODE_VERIFIED)); j = k) { + if (BASE_TABLE(dfa)[j] & MARK_DIFF_ENCODE) + /* loop in current chain */ + goto out; k = DEFAULT_TABLE(dfa)[j]; if (j == k) + /* self loop */ goto out; - if (k < j) - break; /* already verified */ BASE_TABLE(dfa)[j] |= MARK_DIFF_ENCODE; } + /* move mark to verified */ + for (j = i; + (BASE_TABLE(dfa)[j] & MATCH_FLAG_DIFF_ENCODE); + j = k) { + k = DEFAULT_TABLE(dfa)[j]; + if (j < i) + /* jumps to state/chain that has been + * verified + */ + break; + BASE_TABLE(dfa)[j] &= ~MARK_DIFF_ENCODE; + BASE_TABLE(dfa)[j] |= MARK_DIFF_ENCODE_VERIFIED; + } } error = 0;