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[PATCH resend 4.9] hw_random: Don't use a stack buffer in add_early_randomness()

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hw_random carefully avoids using a stack buffer except in
add_early_randomness().  This causes a crash in virtio_rng if
CONFIG_VMAP_STACK=y.

Reported-by: Matt Mullins <mmullins@mmlx.us>
Tested-by: Matt Mullins <mmullins@mmlx.us>
Fixes: d3cc7996473a ("hwrng: fetch randomness only after device init")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---

This fixes a crash in 4.9-rc1.

resending because I typoed the git send-email command.  I stealthily added
Matt's Tested-by, too.

 drivers/char/hw_random/core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 9203f2d130c0..340f96e44642 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -84,14 +84,14 @@ static size_t rng_buffer_size(void)
 
 static void add_early_randomness(struct hwrng *rng)
 {
-	unsigned char bytes[16];
 	int bytes_read;
+	size_t size = min_t(size_t, 16, rng_buffer_size());
 
 	mutex_lock(&reading_mutex);
-	bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
+	bytes_read = rng_get_data(rng, rng_buffer, size, 1);
 	mutex_unlock(&reading_mutex);
 	if (bytes_read > 0)
-		add_device_randomness(bytes, bytes_read);
+		add_device_randomness(rng_buffer, bytes_read);
 }
 
 static inline void cleanup_rng(struct kref *kref)
-- 
2.7.4

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[PATCH resend 4.9] hw_random: Don't use a stack buffer in add_early_randomness() Andy Lutomirski <luto@kernel.org> - 2016-10-17 19:10 +0200
  Re: [PATCH resend 4.9] hw_random: Don't use a stack buffer in add_early_randomness() Stephan Mueller <smueller@chronox.de> - 2016-10-17 19:20 +0200
    Re: [PATCH resend 4.9] hw_random: Don't use a stack buffer in add_early_randomness() Andy Lutomirski <luto@amacapital.net> - 2016-10-17 19:40 +0200
      Re: [PATCH resend 4.9] hw_random: Don't use a stack buffer in add_early_randomness() Stephan Mueller <smueller@chronox.de> - 2016-10-17 20:40 +0200
        Re: [PATCH resend 4.9] hw_random: Don't use a stack buffer in add_early_randomness() Andy Lutomirski <luto@amacapital.net> - 2016-10-17 23:10 +0200
          Re: [PATCH resend 4.9] hw_random: Don't use a stack buffer in add_early_randomness() Stephan Mueller <smueller@chronox.de> - 2016-10-17 23:20 +0200
  Re: [PATCH resend 4.9] hw_random: Don't use a stack buffer in  add_early_randomness() Herbert Xu <herbert@gondor.apana.org.au> - 2016-10-19 06:00 +0200

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