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Christian McDonald Subject: git: dc761982793e - stable/14 - epoch: Fix use-after-free in epoch_trace_report() List-Archive: https://lists.freebsd.org/archives/dev-commits-src-branches X-BeenThere: dev-commits-src-branches@freebsd.org Sender: owner-dev-commits-src-branches@FreeBSD.org List-Id: Commits to the stable branches of the FreeBSD src repository List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: rcm X-Git-Repository: src X-Git-Refname: refs/heads/stable/14 X-Git-Reftype: branch X-Git-Commit: dc761982793e0e4eb360a205f3e73eacc00fd185 Auto-Submitted: auto-generated Date: Wed, 28 Oct 2026 20:41:26 +0000 Message-Id: <6ae25df6.1cfbe.560dafa1@gitrepo.freebsd.org> The branch stable/14 has been updated by rcm: URL: https://cgit.FreeBSD.org/src/commit/?id=dc761982793e0e4eb360a205f3e73eacc00fd185 commit dc761982793e0e4eb360a205f3e73eacc00fd185 Author: R. Christian McDonald AuthorDate: 2026-09-30 13:41:53 +0000 Commit: R. Christian McDonald CommitDate: 2026-10-28 20:38:03 +0000 epoch: Fix use-after-free in epoch_trace_report() epoch_trace_report() assigned the return value of RB_INSERT() back to the new element. When two threads report the same stack concurrently, the loser's RB_INSERT() returns the element already in the tree, and that element was freed while still linked, leaking the new allocation. The next lookup touches freed memory; KASAN catches it as a use-after-free. Keep the return value separate and free the new element instead. The thread that won the race prints the report, so return without printing it a second time. Reviewed by: markj Fixes: 173c062a569b ("Improve EPOCH_TRACE") MFC after: 1 week Sponsored by: Rubicon Communications, LLC ("Netgate") Differential Revision: https://reviews.freebsd.org/D60162 (cherry picked from commit dd5dc8f6e51c5132f2dc885f5c1b0492cdf3052c) --- sys/kern/subr_epoch.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/sys/kern/subr_epoch.c b/sys/kern/subr_epoch.c index 84ccce9f77b2..24147629186a 100644 --- a/sys/kern/subr_epoch.c +++ b/sys/kern/subr_epoch.c @@ -194,6 +194,7 @@ epoch_trace_report(const char *fmt, ...) { va_list ap; struct stackentry se, *new; + bool dup; stack_save(&se.se_stack); @@ -206,10 +207,13 @@ epoch_trace_report(const char *fmt, ...) bcopy(&se.se_stack, &new->se_stack, sizeof(struct stack)); mtx_lock(&epoch_stacks_lock); - new = RB_INSERT(stacktree, &epoch_stacks, new); + dup = RB_INSERT(stacktree, &epoch_stacks, new) != NULL; mtx_unlock(&epoch_stacks_lock); - if (new != NULL) + if (dup) { + /* Lost a race; the other thread reports it. */ free(new, M_STACK); + return; + } } va_start(ap, fmt);