[Devel] [PATCH RH7] vfs: add warning in guard_bio_eod() if truncated_bytes > bvec->bv_len

[Pavel Tikhomirov]

https://jira.sw.ru/browse/PSBM-55105

In bug we crashed in zero_fill_bio when trying to zero memset bio_vec:

struct bio_vec {
  bv_page = 0xffffea0004437500,
  bv_len = 4294948864,
  bv_offset = 0
}

which is bigger than its bio->bi_size = 104448, guard_bio_eod might
lead to these bv_len overflow and is suspicious as quiet recently
in vz7.19.4 we've ported commit 2573b2539875("vfs: make guard_bh_eod()
more generic") which adds bv_len reduction, and before that there
were no crash.

Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
 fs/buffer.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/buffer.c b/fs/buffer.c
index c45200d..b820080 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3009,6 +3009,7 @@ void guard_bio_eod(int rw, struct bio *bio)
 
 	/* Truncate the bio.. */
 	bio->bi_size -= truncated_bytes;
+	WARN_ON(truncated_bytes > bvec->bv_len);
 	bvec->bv_len -= truncated_bytes;
 
 	/* ..and clear the end of the buffer for reads */
-- 
2.9.3