Messages in this thread Patch in this message | | | From | Chunhai Guo <> | Subject | [PATCH] erofs: fix two loop issues when read page beyond EOF | Date | Sat, 8 Jul 2023 14:24:32 +0800 |
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When z_erofs_read_folio() reads a page with an offset far beyond EOF, two issues may occur: - z_erofs_pcluster_readmore() may take a long time to loop when the offset is big enough, which is unnecessary. - For example, it will loop 4691368 times and take about 27 seconds with following case. - offset = 19217289215 - inode_size = 1442672 - z_erofs_do_read_page() may loop infinitely due to the inappropriate truncation in the below statement. Since the offset is 64 bits and min_t() truncates the result to 32 bits. The solution is to replace unsigned int with another 64-bit type, such as erofs_off_t. cur = end - min_t(unsigned int, offset + end - map->m_la, end); - For example: - offset = 0x400160000 - end = 0x370 - map->m_la = 0x160370 - offset + end - map->m_la = 0x400000000 - offset + end - map->m_la = 0x00000000 (truncated as unsigned int) - Expected result: - cur = 0 - Actual result: - cur = 0x370
Signed-off-by: Chunhai Guo <guochunhai@vivo.com> --- fs/erofs/zdata.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c index 5f1890e309c6..6abbd4510076 100644 --- a/fs/erofs/zdata.c +++ b/fs/erofs/zdata.c @@ -972,7 +972,8 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe, struct erofs_map_blocks *const map = &fe->map; const loff_t offset = page_offset(page); bool tight = true, exclusive; - unsigned int cur, end, spiltted; + erofs_off_t cur, end; + unsigned int spiltted; int err = 0; /* register locked file pages as online pages in pack */ @@ -1035,7 +1036,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe, */ tight &= (fe->mode > Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE); - cur = end - min_t(unsigned int, offset + end - map->m_la, end); + cur = end - min_t(erofs_off_t, offset + end - map->m_la, end); if (!(map->m_flags & EROFS_MAP_MAPPED)) { zero_user_segment(page, cur, end); goto next_part; @@ -1841,7 +1842,7 @@ static void z_erofs_pcluster_readmore(struct z_erofs_decompress_frontend *f, } cur = map->m_la + map->m_llen - 1; - while (cur >= end) { + while ((cur >= end) && (cur < i_size_read(inode))) { pgoff_t index = cur >> PAGE_SHIFT; struct page *page; @@ -1876,6 +1877,12 @@ static int z_erofs_read_folio(struct file *file, struct folio *folio) trace_erofs_readpage(page, false); f.headoffset = (erofs_off_t)page->index << PAGE_SHIFT; + /* when trying to read beyond EOF, return zero page directly */ + if (f.headoffset >= i_size_read(inode)) { + zero_user_segment(page, 0, PAGE_SIZE); + return 0; + } + z_erofs_pcluster_readmore(&f, NULL, true); err = z_erofs_do_read_page(&f, page); z_erofs_pcluster_readmore(&f, NULL, false); -- 2.25.1
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