Re: AW: [PATCH 2/2] tty: serial: samsung_tty: Fix a memory leak in s3c24xx_serial_getclk() when iterating clk

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Le 09/06/2023 à 10:57, Walter Harms a écrit :

while we are here ....

perhaps INT_MAX from kernel.h ?

from include/vdso/limits.h

int   deviation = (1 << 30) - 1;

I don't know the initial intent for this value, but it is not the same as MAX_INT.


the part before looks a bit strange

if (ourport->info->has_divslot) {
                         unsigned long div = rate / req_baud;

                         /* The UDIVSLOT register on the newer UARTs allows us to
                          * get a divisor adjustment of 1/16th on the baud clock.
                          *
                          * We don't keep the UDIVSLOT value (the 16ths we
                          * calculated by not multiplying the baud by 16) as it
                          * is easy enough to recalculate.
                          */

                         quot = div / 16;
                         baud = rate / div;
because
    baud=rate/rate/req_baud = req_baud

In math yes. In integer computation, no.
	rate = 20000
	req_baud = 9600

	div = rate / req_baud 		==> 2
	baud = rate / div;		==> 20000 / 2 = 10000

	9600 <> 10000

I don't know if it is the intent, but it is the way it works.

And knowing that:
	calc_deviation = req_baud - baud;
I guess that it is the way it is expected to work.

With your reasoning, calc_deviation would be always 0.

can this be simplyfied ? (or is the numeric required  ?)


Homebrew abs()  kernel.h has a abs() can we use it here ?

include/linux/math.h


             if (calc_deviation < 0)
                         calc_deviation = -calc_deviation;

Ok, why not.


to the patch:

+                       /*
+                        * If we find a better clk, release the previous one, if
+                        * any.
+                        */
+                       if (!IS_ERR(*best_clk))
+                               clk_put(*best_clk);

the intentions are good. *best_clk is user supplied (and should be NULL)

??? Why should it be NULL?

There is only one caller, and the value id &clk, knowing that:
   struct clk *clk = ERR_PTR(-EINVAL);

The code could be changed to have an initial NULL value, but it would'nt bring that much added value, in my PoV.
It would only save a test which is just fine as-is.

filled & released in the next round but IMHO must be valid (is clk).
so no need to check. (ntl clk_put seems to handle NULL and ERR )
    if (!clk || WARN_ON_ONCE(IS_ERR(clk)))
                 return;

My point with "if (!IS_ERR(*best_clk))" is to handle the initial iteration when *best_clk is ERR_PTR(-EINVAL). clk_put() can handle it, but it would WARN in the normal path, so it sounds strange to me.

CJ


JM2C
  wh
________________________________________
Von: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
Gesendet: Freitag, 9. Juni 2023 06:45:39
An: Krzysztof Kozlowski; Alim Akhtar; Greg Kroah-Hartman; Jiri Slaby; Thomas Abraham; Kukjin Kim
Cc: linux-kernel@xxxxxxxxxxxxxxx; kernel-janitors@xxxxxxxxxxxxxxx; Christophe JAILLET; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-samsung-soc@xxxxxxxxxxxxxxx; linux-serial@xxxxxxxxxxxxxxx
Betreff: [PATCH 2/2] tty: serial: samsung_tty: Fix a memory leak in s3c24xx_serial_getclk() when iterating clk

When the best clk is searched, we iterate over all possible clk.

If we find a better match, the previous one, if any, needs to be freed.
If a better match has already been found, we still need to free the new
one, otherwise it leaks.

Fixes: 5f5a7a5578c5 ("serial: samsung: switch to clkdev based clock lookup")
Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
---
This patch is speculative. Review with care.

I think that some clk_put() are also missing somewhere else in the driver
but won't be able to investigate further.
---
  drivers/tty/serial/samsung_tty.c | 8 ++++++++
  1 file changed, 8 insertions(+)

diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/samsung_tty.c
index dd751e7010e3..c07877dd25fa 100644
--- a/drivers/tty/serial/samsung_tty.c
+++ b/drivers/tty/serial/samsung_tty.c
@@ -1488,10 +1488,18 @@ static unsigned int s3c24xx_serial_getclk(struct s3c24xx_uart_port *ourport,
                         calc_deviation = -calc_deviation;

                 if (calc_deviation < deviation) {
+                       /*
+                        * If we find a better clk, release the previous one, if
+                        * any.
+                        */
+                       if (!IS_ERR(*best_clk))
+                               clk_put(*best_clk);
                         *best_clk = clk;
                         best_quot = quot;
                         *clk_num = cnt;
                         deviation = calc_deviation;
+               } else {
+                       clk_put(clk);
                 }
         }

--
2.34.1






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