From: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Subject: 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. Link: http://lkml.kernel.org/r/9d9134359725a965627b7e8f2652069f86f1d1fa.1585233617.git.andreyknvl@xxxxxxxxxx Link: http://lkml.kernel.org/r/de0d3d30ff90776a2a509cc34c7c1c7521bda125.1584655448.git.andreyknvl@xxxxxxxxxx Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Cc: Marco Elver <elver@xxxxxxxxxx> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/kcov.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) --- a/kernel/kcov.c~kcov-fix-potential-use-after-free-in-kcov_remote_start +++ a/kernel/kcov.c @@ -748,6 +748,7 @@ static const struct file_operations kcov 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; } } _
