From 81895a65ec63ee1daec3255dc1a06675d2fbe915 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Wed, 5 Oct 2022 16:43:38 +0200 Subject: treewide: use prandom_u32_max() when possible, part 1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Rather than incurring a division or requesting too many random bytes for the given range, use the prandom_u32_max() function, which only takes the minimum required bytes from the RNG and avoids divisions. This was done mechanically with this coccinelle script: @basic@ expression E; type T; identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32"; typedef u64; @@ ( - ((T)get_random_u32() % (E)) + prandom_u32_max(E) | - ((T)get_random_u32() & ((E) - 1)) + prandom_u32_max(E * XXX_MAKE_SURE_E_IS_POW2) | - ((u64)(E) * get_random_u32() >> 32) + prandom_u32_max(E) | - ((T)get_random_u32() & ~PAGE_MASK) + prandom_u32_max(PAGE_SIZE) ) @multi_line@ identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32"; identifier RAND; expression E; @@ - RAND = get_random_u32(); ... when != RAND - RAND %= (E); + RAND = prandom_u32_max(E); // Find a potential literal @literal_mask@ expression LITERAL; type T; identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32"; position p; @@ ((T)get_random_u32()@p & (LITERAL)) // Add one to the literal. @script:python add_one@ literal << literal_mask.LITERAL; RESULT; @@ value = None if literal.startswith('0x'): value = int(literal, 16) elif literal[0] in '123456789': value = int(literal, 10) if value is None: print("I don't know how to handle %s" % (literal)) cocci.include_match(False) elif value == 2**32 - 1 or value == 2**31 - 1 or value == 2**24 - 1 or value == 2**16 - 1 or value == 2**8 - 1: print("Skipping 0x%x for cleanup elsewhere" % (value)) cocci.include_match(False) elif value & (value + 1) != 0: print("Skipping 0x%x because it's not a power of two minus one" % (value)) cocci.include_match(False) elif literal.startswith('0x'): coccinelle.RESULT = cocci.make_expr("0x%x" % (value + 1)) else: coccinelle.RESULT = cocci.make_expr("%d" % (value + 1)) // Replace the literal mask with the calculated result. @plus_one@ expression literal_mask.LITERAL; position literal_mask.p; expression add_one.RESULT; identifier FUNC; @@ - (FUNC()@p & (LITERAL)) + prandom_u32_max(RESULT) @collapse_ret@ type T; identifier VAR; expression E; @@ { - T VAR; - VAR = (E); - return VAR; + return E; } @drop_var@ type T; identifier VAR; @@ { - T VAR; ... when != VAR } Reviewed-by: Greg Kroah-Hartman Reviewed-by: Kees Cook Reviewed-by: Yury Norov Reviewed-by: KP Singh Reviewed-by: Jan Kara # for ext4 and sbitmap Reviewed-by: Christoph Böhmwalder # for drbd Acked-by: Jakub Kicinski Acked-by: Heiko Carstens # for s390 Acked-by: Ulf Hansson # for mmc Acked-by: Darrick J. Wong # for xfs Signed-off-by: Jason A. Donenfeld --- lib/test_hexdump.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) (limited to 'lib/test_hexdump.c') diff --git a/lib/test_hexdump.c b/lib/test_hexdump.c index 5144899d3c6b..0927f44cd478 100644 --- a/lib/test_hexdump.c +++ b/lib/test_hexdump.c @@ -149,7 +149,7 @@ static void __init test_hexdump(size_t len, int rowsize, int groupsize, static void __init test_hexdump_set(int rowsize, bool ascii) { size_t d = min_t(size_t, sizeof(data_b), rowsize); - size_t len = get_random_int() % d + 1; + size_t len = prandom_u32_max(d) + 1; test_hexdump(len, rowsize, 4, ascii); test_hexdump(len, rowsize, 2, ascii); @@ -208,11 +208,11 @@ static void __init test_hexdump_overflow(size_t buflen, size_t len, static void __init test_hexdump_overflow_set(size_t buflen, bool ascii) { unsigned int i = 0; - int rs = (get_random_int() % 2 + 1) * 16; + int rs = (prandom_u32_max(2) + 1) * 16; do { int gs = 1 << i; - size_t len = get_random_int() % rs + gs; + size_t len = prandom_u32_max(rs) + gs; test_hexdump_overflow(buflen, rounddown(len, gs), rs, gs, ascii); } while (i++ < 3); @@ -223,11 +223,11 @@ static int __init test_hexdump_init(void) unsigned int i; int rowsize; - rowsize = (get_random_int() % 2 + 1) * 16; + rowsize = (prandom_u32_max(2) + 1) * 16; for (i = 0; i < 16; i++) test_hexdump_set(rowsize, false); - rowsize = (get_random_int() % 2 + 1) * 16; + rowsize = (prandom_u32_max(2) + 1) * 16; for (i = 0; i < 16; i++) test_hexdump_set(rowsize, true); -- cgit v1.2.3