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dm verity fec: limit error correction recursion 

If the hash tree itself is sufficiently corrupt in addition to data blocks,
it's possible for error correction to end up in a deep recursive loop,
which eventually causes a kernel panic.  This change limits the
recursion to a reasonable level during a single I/O operation.

Fixes: a739ff3f54 ("dm verity: add support for forward error correction")
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org # v4.5+
This commit is contained in:
Sami Tolvanen 2017-03-15 15:12:23 -07:00 committed by Mike Snitzer
parent 4495c08e84
commit f1a880a93b
2 changed files with 15 additions and 1 deletions
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12
drivers/md/dm-verity-fec.c
View File

@ -439,6 +439,13 @@ int verity_fec_decode(struct dm_verity *v, struct dm_verity_io *io,
if (!verity_fec_is_enabled(v))
return -EOPNOTSUPP;
if (fio->level >= DM_VERITY_FEC_MAX_RECURSION) {
DMWARN_LIMIT("%s: FEC: recursion too deep", v->data_dev->name);
return -EIO;
}
fio->level++;
if (type == DM_VERITY_BLOCK_TYPE_METADATA)
block += v->data_blocks;
@ -470,7 +477,7 @@ int verity_fec_decode(struct dm_verity *v, struct dm_verity_io *io,
if (r < 0) {
r = fec_decode_rsb(v, io, fio, rsb, offset, true);
if (r < 0)
return r;
goto done;
}
if (dest)
@ -480,6 +487,8 @@ int verity_fec_decode(struct dm_verity *v, struct dm_verity_io *io,
r = verity_for_bv_block(v, io, iter, fec_bv_copy);
}
done:
fio->level--;
return r;
}
@ -520,6 +529,7 @@ void verity_fec_init_io(struct dm_verity_io *io)
memset(fio->bufs, 0, sizeof(fio->bufs));
fio->nbufs = 0;
fio->output = NULL;
fio->level = 0;
}
/*

4
drivers/md/dm-verity-fec.h
View File

@ -27,6 +27,9 @@
#define DM_VERITY_FEC_BUF_MAX \
(1 << (PAGE_SHIFT - DM_VERITY_FEC_BUF_RS_BITS))
/* maximum recursion level for verity_fec_decode */
#define DM_VERITY_FEC_MAX_RECURSION 4
#define DM_VERITY_OPT_FEC_DEV "use_fec_from_device"
#define DM_VERITY_OPT_FEC_BLOCKS "fec_blocks"
#define DM_VERITY_OPT_FEC_START "fec_start"
@ -58,6 +61,7 @@ struct dm_verity_fec_io {
unsigned nbufs; /* number of buffers allocated */
u8 *output; /* buffer for corrected output */
size_t output_pos;
unsigned level; /* recursion level */
};
#ifdef CONFIG_DM_VERITY_FEC