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kcov: fix potential use-after-free in kcov_remote_start

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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@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Alexander Potapenko <glider@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Marco Elver <elver@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Link: http://lkml.kernel.org/r/9d9134359725a965627b7e8f2652069f86f1d1fa.1585233617.git.andreyknvl@google.com
Link: http://lkml.kernel.org/r/de0d3d30ff90776a2a509cc34c7c1c7521bda125.1584655448.git.andreyknvl@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrey Konovalov 2020-06-04 16:45:51 -07:00 committed by Linus Torvalds
parent 3c61df3885
commit 67b3d3cca3
1 changed files with 8 additions and 6 deletions
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14
kernel/kcov.c
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@ -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;
}
}