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Date: Thu, 26 Mar 2020 15:44:01 +0100 From: Andrey Konovalov <andreyknvl@...gle.com> To: Dmitry Vyukov <dvyukov@...gle.com> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Alan Stern <stern@...land.harvard.edu>, Andrew Morton <akpm@...ux-foundation.org>, linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org, Alexander Potapenko <glider@...gle.com>, Marco Elver <elver@...gle.com>, Andrey Konovalov <andreyknvl@...gle.com> Subject: [PATCH v4 2/7] kcov: fix potential use-after-free in kcov_remote_start If vmalloc() fails in kcov_remote_start() we'll access remote->kcov without holding kcov_remote_lock, so remote might potentially be freed at that point. Cache kcov pointer in a local variable. Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com> --- kernel/kcov.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/kernel/kcov.c b/kernel/kcov.c index f6bd119c9419..cc5900ac2467 100644 --- a/kernel/kcov.c +++ b/kernel/kcov.c @@ -748,6 +748,7 @@ static const struct file_operations kcov_fops = { void kcov_remote_start(u64 handle) { struct kcov_remote *remote; + struct kcov *kcov; void *area; struct task_struct *t; unsigned int size; @@ -774,16 +775,17 @@ void kcov_remote_start(u64 handle) spin_unlock(&kcov_remote_lock); return; } + kcov = remote->kcov; /* Put in kcov_remote_stop(). */ - kcov_get(remote->kcov); - t->kcov = remote->kcov; + kcov_get(kcov); + t->kcov = kcov; /* * Read kcov fields before unlock to prevent races with * KCOV_DISABLE / kcov_remote_reset(). */ - size = remote->kcov->remote_size; - mode = remote->kcov->mode; - sequence = remote->kcov->sequence; + size = kcov->remote_size; + mode = kcov->mode; + sequence = kcov->sequence; area = kcov_remote_area_get(size); spin_unlock(&kcov_remote_lock); @@ -791,7 +793,7 @@ void kcov_remote_start(u64 handle) area = vmalloc(size * sizeof(unsigned long)); if (!area) { t->kcov = NULL; - kcov_put(remote->kcov); + kcov_put(kcov); return; } } -- 2.26.0.rc2.310.g2932bb562d-goog
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