Messages in this thread | | | Subject | Re: [PATCH RFC] ubi: gluebi: Fix NULL pointer dereference caused by ftl notifier | From | Zhihao Cheng <> | Date | Thu, 12 Oct 2023 16:18:07 +0800 |
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在 2023/10/12 16:04, ZhaoLong Wang 写道: > I'm very happy to receive a reply to the review. > >> 2. fd = open(/dev/ubi0_0, O_WRONLY) >> ubi_open_volume // vol->writers = 1 >> >> P1 P2 >> gluebi_create -> mtd_device_register -> add_mtd_device: >> device_register // dev/mtd1 is visible >> >> fd = open(/dev/mtd1, O_WRONLY) >> gluebi_get_device >> gluebi->desc = ubi_open_volume >> gluebi->desc = ERR_PTR(EBUSY) >> >> ftl_add_mtd >> mtd_read >> gluebi_read >> gluebi->desc is ERR_PTR (√) > > The reproduction steps for situations 2 and 3 have been added to link[1]. > Link: https://bugzilla.kernel.org/show_bug.cgi?id=217992 [1] > >> 3. P1 P2 >> gluebi_create -> mtd_device_register -> add_mtd_device: >> device_register // dev/mtd1 is visible >> >> fd = open(/dev/mtd1, O_WRONLY) >> gluebi_get_device >> gluebi->desc = ubi_open_volume >> >> ftl_add_mtd >> mtd_read >> gluebi_read >> gluebi->desc is not ERR_PTR/NULL >> >> close(fd) >> gluebi_put_device >> ubi_close_volume >> kfree(desc) >> ubi_read(gluebi->desc) // UAF (×) >> > > Yes, it's also a problem. Perhaps it should be set to NULL after > destroying gluebi->desc.
The key point is that 'gluebi->desc' check & usage is not atomic in gluebi_read. So following patch still can't handle situation 3.
> >> >> No need to modify 'gluebi_write' and 'gluebi_erase'. >> > > The patch is as follows: > > diff --git a/drivers/mtd/ubi/gluebi.c b/drivers/mtd/ubi/gluebi.c > index 1b980d15d9fb..8fc6017d1155 100644 > --- a/drivers/mtd/ubi/gluebi.c > +++ b/drivers/mtd/ubi/gluebi.c > @@ -85,6 +85,7 @@ static int gluebi_get_device(struct mtd_info *mtd) > { > struct gluebi_device *gluebi; > int ubi_mode = UBI_READONLY; > + struct ubi_volume_desc *vdesc; > > if (mtd->flags & MTD_WRITEABLE) > ubi_mode = UBI_READWRITE; > @@ -109,12 +110,14 @@ static int gluebi_get_device(struct mtd_info *mtd) > * This is the first reference to this UBI volume via the MTD device > * interface. Open the corresponding volume in read-write mode. > */ > - gluebi->desc = ubi_open_volume(gluebi->ubi_num, gluebi->vol_id, > + vdesc = ubi_open_volume(gluebi->ubi_num, gluebi->vol_id, > ubi_mode); > - if (IS_ERR(gluebi->desc)) { > + if (IS_ERR(vdesc)) { > + gluebi->desc = NULL; > mutex_unlock(&devices_mutex); > - return PTR_ERR(gluebi->desc); > + return PTR_ERR(vdesc); > } > + gluebi->desc = vdesc; > gluebi->refcnt += 1; > mutex_unlock(&devices_mutex); > return 0; > @@ -134,8 +137,10 @@ static void gluebi_put_device(struct mtd_info *mtd) > gluebi = container_of(mtd, struct gluebi_device, mtd); > mutex_lock(&devices_mutex); > gluebi->refcnt -= 1; > - if (gluebi->refcnt == 0) > + if (gluebi->refcnt == 0) { > ubi_close_volume(gluebi->desc); > + gluebi->desc = NULL; > + } > mutex_unlock(&devices_mutex); > } > > @@ -154,9 +159,26 @@ static int gluebi_read(struct mtd_info *mtd, loff_t > from, size_t len, > size_t *retlen, unsigned char *buf) > { > int err = 0, lnum, offs, bytes_left; > - struct gluebi_device *gluebi; > + struct gluebi_device *gluebi = container_of(mtd, struct gluebi_device, > + mtd); > + int isnt_get = unlikely(gluebi->desc == NULL) ? 1 : 0; > + > + /** > + * In normal case, the UBI volume desc has been initialized by > + * ->_get_device(). However, in the ftl notifier process, the > + * ->_get_device() is not executed in advance and the MTD device > + * is directly scanned which cause null pointe dereference. > + * Therefore, try to get the MTD device here. > + */ > + if (unlikely(isnt_get)) { > + err = __get_mtd_device(mtd); > + if (err) { > + err_msg("cannot get MTD device %d, UBI device %d, volume > %d, error %d", > + mtd->index, gluebi->ubi_num, gluebi->vol_id, err); > + return err; > + } > + } > > - gluebi = container_of(mtd, struct gluebi_device, mtd); > lnum = div_u64_rem(from, mtd->erasesize, &offs); > bytes_left = len; > while (bytes_left) { > @@ -176,6 +198,9 @@ static int gluebi_read(struct mtd_info *mtd, loff_t > from, size_t len, > } > > *retlen = len - bytes_left; > + > + if (unlikely(isnt_get)) > + __put_mtd_device(mtd); > return err; > } > > > > .
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