[ 34/37] tpm: Propagate error from tpm_transmit to fix a timeout hang

From: Greg Kroah-Hartman
Date: Thu Oct 18 2012 - 23:18:07 EST

3.0-stable review patch. If anyone has any objections, please let me know.


From: Peter Huewe <peter.huewe@xxxxxxxxxxxx>

commit abce9ac292e13da367bbd22c1f7669f988d931ac upstream.

tpm_write calls tpm_transmit without checking the return value and
assigns the return value unconditionally to chip->pending_data, even if
it's an error value.
This causes three bugs.

So if we write to /dev/tpm0 with a tpm_param_size bigger than
TPM_BUFSIZE=0x1000 (e.g. 0x100a)
and a bufsize also bigger than TPM_BUFSIZE (e.g. 0x100a)
tpm_transmit returns -E2BIG which is assigned to chip->pending_data as
-7, but tpm_write returns that TPM_BUFSIZE bytes have been successfully
been written to the TPM, altough this is not true (bug #1).

As we did write more than than TPM_BUFSIZE bytes but tpm_write reports
that only TPM_BUFSIZE bytes have been written the vfs tries to write
the remaining bytes (in this case 10 bytes) to the tpm device driver via
tpm_write which then blocks at

/* cannot perform a write until the read has cleared
either via tpm_read or a user_read_timer timeout */
while (atomic_read(&chip->data_pending) != 0)

for 60 seconds, since data_pending is -7 and nobody is able to
read it (since tpm_read luckily checks if data_pending is greater than
0) (#bug 2).

After that the remaining bytes are written to the TPM which are
interpreted by the tpm as a normal command. (bug #3)
So if the last bytes of the command stream happen to be a e.g.
tpm_force_clear this gets accidentally sent to the TPM.

This patch fixes all three bugs, by propagating the error code of
tpm_write and returning -E2BIG if the input buffer is too big,
since the response from the tpm for a truncated value is bogus anyway.
Moreover it returns -EBUSY to userspace if there is a response ready to be

Signed-off-by: Peter Huewe <peter.huewe@xxxxxxxxxxxx>
Signed-off-by: Kent Yoder <key@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/char/tpm/tpm.c | 21 ++++++++++++++-------
1 file changed, 14 insertions(+), 7 deletions(-)

--- a/drivers/char/tpm/tpm.c
+++ b/drivers/char/tpm/tpm.c
@@ -1019,17 +1019,20 @@ ssize_t tpm_write(struct file *file, con
size_t size, loff_t *off)
struct tpm_chip *chip = file->private_data;
- size_t in_size = size, out_size;
+ size_t in_size = size;
+ ssize_t out_size;

/* cannot perform a write until the read has cleared
- either via tpm_read or a user_read_timer timeout */
- while (atomic_read(&chip->data_pending) != 0)
- msleep(TPM_TIMEOUT);
- mutex_lock(&chip->buffer_mutex);
+ either via tpm_read or a user_read_timer timeout.
+ This also prevents splitted buffered writes from blocking here.
+ */
+ if (atomic_read(&chip->data_pending) != 0)
+ return -EBUSY;

if (in_size > TPM_BUFSIZE)
- in_size = TPM_BUFSIZE;
+ return -E2BIG;
+ mutex_lock(&chip->buffer_mutex);

if (copy_from_user
(chip->data_buffer, (void __user *) buf, in_size)) {
@@ -1039,6 +1042,10 @@ ssize_t tpm_write(struct file *file, con

/* atomic tpm command send and result receive */
out_size = tpm_transmit(chip, chip->data_buffer, TPM_BUFSIZE);
+ if (out_size < 0) {
+ mutex_unlock(&chip->buffer_mutex);
+ return out_size;
+ }

atomic_set(&chip->data_pending, out_size);

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