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dm: fix truncated status strings

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Avoid returning a truncated table or status string instead of setting
the DM_BUFFER_FULL_FLAG when the last target of a table fills the
buffer.

When processing a table or status request, the function retrieve_status
calls ti->type->status. If ti->type->status returns non-zero,
retrieve_status assumes that the buffer overflowed and sets
DM_BUFFER_FULL_FLAG.

However, targets don't return non-zero values from their status method
on overflow. Most targets returns always zero.

If a buffer overflow happens in a target that is not the last in the
table, it gets noticed during the next iteration of the loop in
retrieve_status; but if a buffer overflow happens in the last target, it
goes unnoticed and erroneously truncated data is returned.

In the current code, the targets behave in the following way:
* dm-crypt returns -ENOMEM if there is not enough space to store the
  key, but it returns 0 on all other overflows.
* dm-thin returns errors from the status method if a disk error happened.
  This is incorrect because retrieve_status doesn't check the error
  code, it assumes that all non-zero values mean buffer overflow.
* all the other targets always return 0.

This patch changes the ti->type->status function to return void (because
most targets don't use the return code). Overflow is detected in
retrieve_status: if the status method fills up the remaining space
completely, it is assumed that buffer overflow happened.

Cc: stable@vger.kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mikulas Patocka
2013-03-01 22:45:44 +00:00
committed by Alasdair G Kergon
parent 16245bdc9d
commit fd7c092e71
13 changed files with 99 additions and 115 deletions
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7
drivers/md/dm-linear.c
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@@ -95,8 +95,8 @@ static int linear_map(struct dm_target *ti, struct bio *bio)
return DM_MAPIO_REMAPPED;
}
static int linear_status(struct dm_target *ti, status_type_t type,
unsigned status_flags, char *result, unsigned maxlen)
static void linear_status(struct dm_target *ti, status_type_t type,
unsigned status_flags, char *result, unsigned maxlen)
{
struct linear_c *lc = (struct linear_c *) ti->private;
@@ -110,7 +110,6 @@ static int linear_status(struct dm_target *ti, status_type_t type,
(unsigned long long)lc->start);
break;
}
return 0;
}
static int linear_ioctl(struct dm_target *ti, unsigned int cmd,
@@ -155,7 +154,7 @@ static int linear_iterate_devices(struct dm_target *ti,
static struct target_type linear_target = {
.name = "linear",
.version = {1, 2, 0},
.version = {1, 2, 1},
.module = THIS_MODULE,
.ctr = linear_ctr,
.dtr = linear_dtr,