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mtd: sf: Make sf_mtd.c more robust

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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>
This commit is contained in:
Boris Brezillon 2018-12-02 10:54:32 +01:00 committed by Jagan Teki
parent 7371944a71
commit 08898e8b22
1 changed files with 36 additions and 3 deletions
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39
drivers/mtd/spi/sf_mtd.c
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@ -18,6 +18,9 @@ static int spi_flash_mtd_erase(struct mtd_info *mtd, struct erase_info *instr)
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 @@ static int spi_flash_mtd_read(struct mtd_info *mtd, loff_t from, size_t len,
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 @@ static int spi_flash_mtd_write(struct mtd_info *mtd, loff_t to, size_t len,
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 spi_flash_mtd_register(struct spi_flash *flash)
{
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 @@ int spi_flash_mtd_register(struct spi_flash *flash)
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);
}