From 9ef8eb6104527bfe9ed31f7a4ffa721390adf9a8 Mon Sep 17 00:00:00 2001 From: Phillip Lougher Date: Thu, 20 Oct 2022 23:36:14 +0100 Subject: squashfs: fix read regression introduced in readahead code Patch series "squashfs: fix some regressions introduced in the readahead code". This patchset fixes 3 regressions introduced by the recent readahead code changes. The first regression is causing "snaps" to randomly fail after a couple of hours or days, which how the regression came to light. This patch (of 3): If a file isn't a whole multiple of the page size, the last page will have trailing bytes unfilled. There was a mistake in the readahead code which did this. In particular it incorrectly assumed that the last page in the readahead page array (page[nr_pages - 1]) will always contain the last page in the block, which if we're at file end, will be the page that needs to be zero filled. But the readahead code may not return the last page in the block, which means it is unmapped and will be skipped by the decompressors (a temporary buffer used). In this case the zero filling code will zero out the wrong page, leading to data corruption. Fix this by by extending the "page actor" to return the last page if present, or NULL if a temporary buffer was used. Link: https://lkml.kernel.org/r/20221020223616.7571-1-phillip@squashfs.org.uk Link: https://lkml.kernel.org/r/20221020223616.7571-2-phillip@squashfs.org.uk Fixes: 8fc78b6fe24c ("squashfs: implement readahead") Link: https://lore.kernel.org/lkml/b0c258c3-6dcf-aade-efc4-d62a8b3a1ce2@alu.unizg.hr/ Signed-off-by: Phillip Lougher Reported-by: Mirsad Goran Todorovac Tested-by: Mirsad Goran Todorovac Tested-by: Slade Watkins Tested-by: Bagas Sanjaya Reported-by: Marc Miltenberger Cc: Dimitri John Ledkov Cc: Hsin-Yi Wang Cc: Thorsten Leemhuis Cc: Signed-off-by: Andrew Morton --- fs/squashfs/file.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'fs/squashfs/file.c') diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c index e56510964b22..e526eb7a1658 100644 --- a/fs/squashfs/file.c +++ b/fs/squashfs/file.c @@ -557,6 +557,7 @@ static void squashfs_readahead(struct readahead_control *ractl) int res, bsize; u64 block = 0; unsigned int expected; + struct page *last_page; nr_pages = __readahead_batch(ractl, pages, max_pages); if (!nr_pages) @@ -593,15 +594,15 @@ static void squashfs_readahead(struct readahead_control *ractl) res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor); - squashfs_page_actor_free(actor); + last_page = squashfs_page_actor_free(actor); if (res == expected) { int bytes; /* Last page (if present) may have trailing bytes not filled */ bytes = res % PAGE_SIZE; - if (pages[nr_pages - 1]->index == file_end && bytes) - memzero_page(pages[nr_pages - 1], bytes, + if (index == file_end && bytes && last_page) + memzero_page(last_page, bytes, PAGE_SIZE - bytes); for (i = 0; i < nr_pages; i++) { -- cgit v1.2.3 From c9199de82bad03bceb94ec3c5195c879d7e11911 Mon Sep 17 00:00:00 2001 From: Phillip Lougher Date: Thu, 20 Oct 2022 23:36:15 +0100 Subject: squashfs: fix extending readahead beyond end of file The readahead code will try to extend readahead to the entire size of the Squashfs data block. But, it didn't take into account that the last block at the end of the file may not be a whole block. In this case, the code would extend readahead to beyond the end of the file, leaving trailing pages. Fix this by only requesting the expected number of pages. Link: https://lkml.kernel.org/r/20221020223616.7571-3-phillip@squashfs.org.uk Fixes: 8fc78b6fe24c ("squashfs: implement readahead") Signed-off-by: Phillip Lougher Tested-by: Bagas Sanjaya Reported-by: Marc Miltenberger Cc: Dimitri John Ledkov Cc: Hsin-Yi Wang Cc: Mirsad Goran Todorovac Cc: Slade Watkins Cc: Thorsten Leemhuis Cc: Signed-off-by: Andrew Morton --- fs/squashfs/file.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) (limited to 'fs/squashfs/file.c') diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c index e526eb7a1658..f0afd4d6fd30 100644 --- a/fs/squashfs/file.c +++ b/fs/squashfs/file.c @@ -559,6 +559,12 @@ static void squashfs_readahead(struct readahead_control *ractl) unsigned int expected; struct page *last_page; + expected = start >> msblk->block_log == file_end ? + (i_size_read(inode) & (msblk->block_size - 1)) : + msblk->block_size; + + max_pages = (expected + PAGE_SIZE - 1) >> PAGE_SHIFT; + nr_pages = __readahead_batch(ractl, pages, max_pages); if (!nr_pages) break; @@ -567,13 +573,10 @@ static void squashfs_readahead(struct readahead_control *ractl) goto skip_pages; index = pages[0]->index >> shift; + if ((pages[nr_pages - 1]->index >> shift) != index) goto skip_pages; - expected = index == file_end ? - (i_size_read(inode) & (msblk->block_size - 1)) : - msblk->block_size; - if (index == file_end && squashfs_i(inode)->fragment_block != SQUASHFS_INVALID_BLK) { res = squashfs_readahead_fragment(pages, nr_pages, -- cgit v1.2.3 From e11c4e088be4c39d17f304fcf331670891905f42 Mon Sep 17 00:00:00 2001 From: Phillip Lougher Date: Thu, 20 Oct 2022 23:36:16 +0100 Subject: squashfs: fix buffer release race condition in readahead code Fix a buffer release race condition, where the error value was used after release. Link: https://lkml.kernel.org/r/20221020223616.7571-4-phillip@squashfs.org.uk Fixes: b09a7a036d20 ("squashfs: support reading fragments in readahead call") Signed-off-by: Phillip Lougher Tested-by: Bagas Sanjaya Reported-by: Marc Miltenberger Cc: Dimitri John Ledkov Cc: Hsin-Yi Wang Cc: Mirsad Goran Todorovac Cc: Slade Watkins Cc: Thorsten Leemhuis Cc: Signed-off-by: Andrew Morton --- fs/squashfs/file.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'fs/squashfs/file.c') diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c index f0afd4d6fd30..8ba8c4c50770 100644 --- a/fs/squashfs/file.c +++ b/fs/squashfs/file.c @@ -506,8 +506,9 @@ static int squashfs_readahead_fragment(struct page **page, squashfs_i(inode)->fragment_size); struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info; unsigned int n, mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1; + int error = buffer->error; - if (buffer->error) + if (error) goto out; expected += squashfs_i(inode)->fragment_offset; @@ -529,7 +530,7 @@ static int squashfs_readahead_fragment(struct page **page, out: squashfs_cache_put(buffer); - return buffer->error; + return error; } static void squashfs_readahead(struct readahead_control *ractl) -- cgit v1.2.3