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From: "priour.be at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug analyzer/109365] New: Double delete yields -Wanalyzer-use-after-free instead of -Wanalyzer-double-free Date: Fri, 31 Mar 2023 20:31:53 +0000 [thread overview] Message-ID: <bug-109365-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109365 Bug ID: 109365 Summary: Double delete yields -Wanalyzer-use-after-free instead of -Wanalyzer-double-free Product: gcc Version: 13.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: analyzer Assignee: dmalcolm at gcc dot gnu.org Reporter: priour.be at gmail dot com Target Milestone: --- Target: x86_64-pc-linux-gnu Build: 13.0.1 20230328 (experimental) Double delete does not result in a -Wanalyzer-double-free warning as expected, but rather into -Wanalyzer-use-after-free warning. Using the following reproducer: // file ../../double_delete_test.cpp struct A {int a; int b;}; int main () { A* a = new A(); delete a; delete a; return 0; } Then compiling with ./xg++ -B. -S -fanalyzer -Wanalyzer-double-free ../../double_delete_test.cpp ../../double_delete_test.cpp: In function ‘int main()’: ../../double_delete_test.cpp:9:1: warning: use after ‘delete’ of ‘a’ [CWE-416] [-Wanalyzer-use-after-free] 9 | } | ^ ‘int main()’: events 1-7 | | 5 | A* a = new A(); | | ^ | | | | | (1) state of ‘&HEAP_ALLOCATED_REGION(10)’: ‘start’ -> ‘nonnull’ (NULL origin) | 6 | delete a; | | ~~~~~~~~ | | | | | | | (3) ...to here | | | (4) deleted here | | (2) following ‘true’ branch... | 7 | delete a; | | ~~~~~~~~ | | | | | | | (6) ...to here | | (5) following ‘true’ branch... | 8 | return 0; | 9 | } | | ~ | | | | | (7) use after ‘delete’ of ‘a’; deleted at (4) | I also attempted with -fno-exception, but no impact was observer on the graphs nor the output. With the addition of -fanalyzer-fine-grained, I observed than each delete statement is actually split into two: delete a; becomes in the ipa form <bb 3> : *a.0_9 ={v} {CLOBBER}; operator delete (a.0_9, 8); The exploded-graph shows that the second '*a.1_12 ={v} {CLOBBER};' dereference is responsible for the -Wanalyzer-use-after-free, and changes the state of the allocated region from 'freed' to 'stop', which causes the actual following 'operator delete' to not be detected as a double free. I am still familiarizing myself with the gimplification and ssa passes, so I'm yet unsure as to how to tackle this. I'm still looking into this though, and would gladly receive your pointers. (Note: sorry David, I've binged through bugzilla doc and gcc bugs page yet I cannot seem to find the way to add this to the 'analyzer-c++' block, nor do I see the option in the advanced fields.)
next reply other threads:[~2023-03-31 20:31 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-03-31 20:31 priour.be at gmail dot com [this message] 2023-03-31 20:34 ` [Bug analyzer/109365] " dmalcolm at gcc dot gnu.org 2023-03-31 20:37 ` priour.be at gmail dot com 2023-07-05 11:31 ` vultkayn at gcc dot gnu.org 2023-07-07 11:28 ` vultkayn at gcc dot gnu.org 2023-07-21 22:22 ` dmalcolm at gcc dot gnu.org 2023-07-26 17:10 ` vultkayn at gcc dot gnu.org
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