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authorOmar Sandoval <osandov@fb.com>2017-02-10 15:03:35 -0800
committerChris Mason <clm@fb.com>2017-02-10 19:11:03 -0800
commit6e78b3f7a193546b1c00a6d084596e774f147169 (patch)
treef9cb50e4e7ad54fa71359dab4aba0fe742987e0e
parentf3c7bfbda7ce03c603b4292efddc944228dccc55 (diff)
downloadlinux-bcache-6e78b3f7a193546b1c00a6d084596e774f147169.tar.zst
Btrfs: fix btrfs_decompress_buf2page()
If btrfs_decompress_buf2page() is handed a bio with its page in the middle of the working buffer, then we adjust the offset into the working buffer. After we copy into the bio, we advance the iterator by the number of bytes we copied. Then, we have some logic to handle the case of discontiguous pages and adjust the offset into the working buffer again. However, if we didn't advance the bio to a new page, we may enter this case in error, essentially repeating the adjustment that we already made when we entered the function. The end result is bogus data in the bio. Previously, we only checked for this case when we advanced to a new page, but the conversion to bio iterators changed that. This restores the old, correct behavior. A case I saw when testing with zlib was: buf_start = 42769 total_out = 46865 working_bytes = total_out - buf_start = 4096 start_byte = 45056 The condition (total_out > start_byte && buf_start < start_byte) is true, so we adjust the offset: buf_offset = start_byte - buf_start = 2287 working_bytes -= buf_offset = 1809 current_buf_start = buf_start = 42769 Then, we copy bytes = min(bvec.bv_len, PAGE_SIZE - buf_offset, working_bytes) = 1809 buf_offset += bytes = 4096 working_bytes -= bytes = 0 current_buf_start += bytes = 44578 After bio_advance(), we are still in the same page, so start_byte is the same. Then, we check (total_out > start_byte && current_buf_start < start_byte), which is true! So, we adjust the values again: buf_offset = start_byte - buf_start = 2287 working_bytes = total_out - start_byte = 1809 current_buf_start = buf_start + buf_offset = 45056 But note that working_bytes was already zero before this, so we should have stopped copying. Fixes: 974b1adc3b10 ("btrfs: use bio iterators for the decompression handlers") Reported-by: Pat Erley <pat-lkml@erley.org> Reviewed-by: Chris Mason <clm@fb.com> Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Chris Mason <clm@fb.com> Reviewed-by: Liu Bo <bo.li.liu@oracle.com> Tested-by: Liu Bo <bo.li.liu@oracle.com>
-rw-r--r--fs/btrfs/compression.c39
1 files changed, 24 insertions, 15 deletions
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 7f390849343b..c4444d6f439f 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -1024,6 +1024,7 @@ int btrfs_decompress_buf2page(char *buf, unsigned long buf_start,
unsigned long buf_offset;
unsigned long current_buf_start;
unsigned long start_byte;
+ unsigned long prev_start_byte;
unsigned long working_bytes = total_out - buf_start;
unsigned long bytes;
char *kaddr;
@@ -1071,26 +1072,34 @@ int btrfs_decompress_buf2page(char *buf, unsigned long buf_start,
if (!bio->bi_iter.bi_size)
return 0;
bvec = bio_iter_iovec(bio, bio->bi_iter);
-
+ prev_start_byte = start_byte;
start_byte = page_offset(bvec.bv_page) - disk_start;
/*
- * make sure our new page is covered by this
- * working buffer
+ * We need to make sure we're only adjusting
+ * our offset into compression working buffer when
+ * we're switching pages. Otherwise we can incorrectly
+ * keep copying when we were actually done.
*/
- if (total_out <= start_byte)
- return 1;
+ if (start_byte != prev_start_byte) {
+ /*
+ * make sure our new page is covered by this
+ * working buffer
+ */
+ if (total_out <= start_byte)
+ return 1;
- /*
- * the next page in the biovec might not be adjacent
- * to the last page, but it might still be found
- * inside this working buffer. bump our offset pointer
- */
- if (total_out > start_byte &&
- current_buf_start < start_byte) {
- buf_offset = start_byte - buf_start;
- working_bytes = total_out - start_byte;
- current_buf_start = buf_start + buf_offset;
+ /*
+ * the next page in the biovec might not be adjacent
+ * to the last page, but it might still be found
+ * inside this working buffer. bump our offset pointer
+ */
+ if (total_out > start_byte &&
+ current_buf_start < start_byte) {
+ buf_offset = start_byte - buf_start;
+ working_bytes = total_out - start_byte;
+ current_buf_start = buf_start + buf_offset;
+ }
}
}