mtd: sf: Make sf_mtd.c more robust
SPI flash based MTD devs can be registered/unregistered at any time
through the sf probe command or the spi_flash_free() function.
This commit does not try to fix the root cause as it would probably
require rewriting most of the code and have an mtd_info object
instance per spi_flash object (not to mention that the the spi-flash
layer is likely to be replaced by a spi-nor layer ported from Linux).
Instead, we try to be as safe as can be by checking the code returned
by del_mtd_device() and complain loudly when there's nothing we can
do about the deregistration failure. When that happens we also reset
sf_mtd_info.priv to NULL, and check for NULL pointer in the mtd hooks
so that -ENODEV is returned instead of hitting a NULL pointer
dereference exception when the MTD instance is later accessed by a user.
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Tested-by: Heiko Schocher <hs@denx.de>
diff --git a/drivers/mtd/spi/sf_mtd.c b/drivers/mtd/spi/sf_mtd.c
index aabbc35..68c3600 100644
--- a/drivers/mtd/spi/sf_mtd.c
+++ b/drivers/mtd/spi/sf_mtd.c
@@ -18,6 +18,9 @@
struct spi_flash *flash = mtd->priv;
int err;
+ if (!flash)
+ return -ENODEV;
+
instr->state = MTD_ERASING;
err = spi_flash_erase(flash, instr->addr, instr->len);
@@ -39,6 +42,9 @@
struct spi_flash *flash = mtd->priv;
int err;
+ if (!flash)
+ return -ENODEV;
+
err = spi_flash_read(flash, from, len, buf);
if (!err)
*retlen = len;
@@ -52,6 +58,9 @@
struct spi_flash *flash = mtd->priv;
int err;
+ if (!flash)
+ return -ENODEV;
+
err = spi_flash_write(flash, to, len, buf);
if (!err)
*retlen = len;
@@ -76,8 +85,13 @@
{
int ret;
- if (sf_mtd_registered)
- del_mtd_device(&sf_mtd_info);
+ if (sf_mtd_registered) {
+ ret = del_mtd_device(&sf_mtd_info);
+ if (ret)
+ return ret;
+
+ sf_mtd_registered = false;
+ }
sf_mtd_registered = false;
memset(&sf_mtd_info, 0, sizeof(sf_mtd_info));
@@ -110,5 +124,24 @@
void spi_flash_mtd_unregister(void)
{
- del_mtd_device(&sf_mtd_info);
+ int ret;
+
+ if (!sf_mtd_registered)
+ return;
+
+ ret = del_mtd_device(&sf_mtd_info);
+ if (!ret) {
+ sf_mtd_registered = false;
+ return;
+ }
+
+ /*
+ * Setting mtd->priv to NULL is the best we can do. Thanks to that,
+ * the MTD layer can still call mtd hooks without risking a
+ * use-after-free bug. Still, things should be fixed to prevent the
+ * spi_flash object from being destroyed when del_mtd_device() fails.
+ */
+ sf_mtd_info.priv = NULL;
+ printf("Failed to unregister MTD %s and the spi_flash object is going away: you're in deep trouble!",
+ sf_mtd_info.name);
}