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mm: fix memcpy_from_file_folio() integer underflow

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If we have a HIGHMEM system with a large folio, 'offset' may be larger
than PAGE_SIZE, and so min_t will cap at 'len' instead of the intended
end-of-page.  That can overflow into the next page which is likely to be
unmapped and fault, but could theoretically copy the wrong data.

Link: https://lkml.kernel.org/r/Y919vmSrtAgsf6K3@casper.infradead.org
Fixes: 00cdf76012 ("mm: add memcpy_from_file_folio()")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2023-02-03 16:28:40 -05:00 committed by Andrew Morton
parent 6f74c0ec20
commit c643e6ebed
1 changed files with 3 additions and 2 deletions
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5
include/linux/highmem.h
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@ -431,9 +431,10 @@ static inline size_t memcpy_from_file_folio(char *to, struct folio *folio,
size_t offset = offset_in_folio(folio, pos);
char *from = kmap_local_folio(folio, offset);
if (folio_test_highmem(folio))
if (folio_test_highmem(folio)) {
offset = offset_in_page(offset);
len = min_t(size_t, len, PAGE_SIZE - offset);
else
} else
len = min(len, folio_size(folio) - offset);
memcpy(to, from, len);