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Subject[PATCH] posix-timers: Protect posix clock array access against speculation
The (clock) id argument of clockid_to_kclock() comes straight from user
space via various syscalls and is used as index into the posix_clocks
array.

Protect it against spectre v1 array out of bounds speculation.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
---
kernel/time/posix-timers.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -50,6 +50,7 @@
#include <linux/export.h>
#include <linux/hashtable.h>
#include <linux/compat.h>
+#include <linux/nospec.h>

#include "timekeeping.h"
#include "posix-timers.h"
@@ -1346,11 +1347,14 @@ static const struct k_clock * const posi

static const struct k_clock *clockid_to_kclock(const clockid_t id)
{
+ clockid_t idx = id;
+
if (id < 0)
return (id & CLOCKFD_MASK) == CLOCKFD ?
&clock_posix_dynamic : &clock_posix_cpu;

if (id >= ARRAY_SIZE(posix_clocks) || !posix_clocks[id])
return NULL;
- return posix_clocks[id];
+
+ return posix_clocks[array_index_nospec(idx, ARRAY_SIZE(posix_clocks))];
}
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