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ANDROID: dm verity fec: limit error correction recursion

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If verity tree itself is sufficiently corrupted in addition to data
blocks, it's possible for error correction to end up in a deep recursive
error correction loop that eventually causes a kernel panic as follows:

[   14.728962] [<ffffffc0008c1a14>] verity_fec_decode+0xa8/0x138
[   14.734691] [<ffffffc0008c3ee0>] verity_verify_level+0x11c/0x180
[   14.740681] [<ffffffc0008c482c>] verity_hash_for_block+0x88/0xe0
[   14.746671] [<ffffffc0008c1508>] fec_decode_rsb+0x318/0x75c
[   14.752226] [<ffffffc0008c1a14>] verity_fec_decode+0xa8/0x138
[   14.757956] [<ffffffc0008c3ee0>] verity_verify_level+0x11c/0x180
[   14.763944] [<ffffffc0008c482c>] verity_hash_for_block+0x88/0xe0

This change limits the recursion to a reasonable level during a single
I/O operation.

Bug: 28943429
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Change-Id: I0a7ebff331d259c59a5e03c81918cc1613c3a766
(cherry picked from commit f4b9e40597e73942d2286a73463c55f26f61bfa7)
Git-commit: 249d2baf9b
Git-repo: https://android.googlesource.com/kernel/common
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>
This commit is contained in:
Sami Tolvanen 2016-06-03 14:06:14 -07:00 • committed by Vikram Mulukutla
parent 590c510b92
commit c57ee8ea9e
2 changed files with 14 additions and 1 deletions
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11
drivers/md/dm-verity-fec.c
View file

@ -442,6 +442,13 @@ 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;
@ -475,7 +482,7 @@ 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)
@ -485,6 +492,8 @@ 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;
}

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

@ -28,6 +28,9 @@
#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"
@ -61,6 +64,7 @@ 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