Re: [RESEND PATCH] i2c: s3c2410: fix possible NULL pointer deref on read message after write

Wolfram Sang
2021-05-28T08:17:51Z

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On Wed, May 26, 2021 at 08:39:37AM -0400, Krzysztof Kozlowski wrote:
> Interrupt handler processes multiple message write requests one after
> another, till the driver message queue is drained. However if driver
> encounters a read message without preceding START, it stops the I2C
> transfer as it is an invalid condition for the controller. At least the
> comment describes a requirement "the controller forces us to send a new
> START when we change direction". This stop results in clearing the
> message queue (i2c->msg = NULL).
>
> The code however immediately jumped back to label "retry_write" which
> dereferenced the "i2c->msg" making it a possible NULL pointer
> dereference.
>
> The Coverity analysis:
> 1. Condition !is_msgend(i2c), taking false branch.
> if (!is_msgend(i2c)) {
>
> 2. Condition !is_lastmsg(i2c), taking true branch.
> } else if (!is_lastmsg(i2c)) {
>
> 3. Condition i2c->msg->flags & 1, taking true branch.
> if (i2c->msg->flags & I2C_M_RD) {
>
> 4. write_zero_model: Passing i2c to s3c24xx_i2c_stop, which sets i2c->msg to NULL.
> s3c24xx_i2c_stop(i2c, -EINVAL);
>
> 5. Jumping to label retry_write.
> goto retry_write;
>
> 6. var_deref_model: Passing i2c to is_msgend, which dereferences null i2c->msg.
> if (!is_msgend(i2c)) {"
>
> All previous calls to s3c24xx_i2c_stop() in this interrupt service
> routine are followed by jumping to end of function (acknowledging
> the interrupt and returning). This seems a reasonable choice also here
> since message buffer was entirely emptied.
>
> Addresses-Coverity: Explicit null dereferenced
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
>

Applied to for-current, thanks!

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