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| author | Matthew Wilcox (Oracle) <willy@infradead.org> | 2022-02-23 18:59:18 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-03-02 13:47:47 +0300 |
| commit | f89903ae99bd02379e8b84d487ce302f122c4ef1 (patch) | |
| tree | 81464352e3a932522afef0f5928ed5e2da6ee518 /mm | |
| parent | 1e7beca2829960d7ec407d0a7b3f5243c6344412 (diff) | |
| download | linux-f89903ae99bd02379e8b84d487ce302f122c4ef1.tar.xz | |
mm/filemap: Fix handling of THPs in generic_file_buffered_read()
When a THP is present in the page cache, we can return it several times,
leading to userspace seeing the same data repeatedly if doing a read()
that crosses a 64-page boundary. This is probably not a security issue
(since the data all comes from the same file), but it can be interpreted
as a transient data corruption issue. Fortunately, it is very rare as
it can only occur when CONFIG_READ_ONLY_THP_FOR_FS is enabled, and it can
only happen to executables. We don't often call read() on executables.
This bug is fixed differently in v5.17 by commit 6b24ca4a1a8d
("mm: Use multi-index entries in the page cache"). That commit is
unsuitable for backporting, so fix this in the clearest way. It
sacrifices a little performance for clarity, but this should never
be a performance path in these kernel versions.
Fixes: cbd59c48ae2b ("mm/filemap: use head pages in generic_file_buffered_read")
Cc: stable@vger.kernel.org # v5.15, v5.16
Link: https://lore.kernel.org/r/df3b5d1c-a36b-2c73-3e27-99e74983de3a@suse.cz/
Analyzed-by: Adam Majer <amajer@suse.com>
Analyzed-by: Dirk Mueller <dmueller@suse.com>
Bisected-by: Takashi Iwai <tiwai@suse.de>
Reported-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/filemap.c | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/mm/filemap.c b/mm/filemap.c index 82a17c35eb96..1293c3409e42 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2354,8 +2354,12 @@ static void filemap_get_read_batch(struct address_space *mapping, break; if (PageReadahead(head)) break; - xas.xa_index = head->index + thp_nr_pages(head) - 1; - xas.xa_offset = (xas.xa_index >> xas.xa_shift) & XA_CHUNK_MASK; + if (PageHead(head)) { + xas_set(&xas, head->index + thp_nr_pages(head)); + /* Handle wrap correctly */ + if (xas.xa_index - 1 >= max) + break; + } continue; put_page: put_page(head); |