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Detect all overflows in BitTorrent parse_bencoding_integer.

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The previous check (integer > (off_t) integer * 10) did not detect all
overflows.  Examples with 32-bit off_t:

integer = 0x1C71C71D (0x100000000/9 rounded up);
integer * 10 = 0x11C71C722, wraps to 0x1C71C722 which is > integer.

integer = 0x73333333;
integer * 10 = 0x47FFFFFFE, wraps to 0x7FFFFFFE which is > integer.

Examples with 64-bit off_t:

integer = 0x1C71C71C71C71C72 (0x10000000000000000/9 rounded up);
integer * 10 = 0x11C71C71C71C71C74, wraps to 0x1C71C71C71C71C74
which is > integer.

integer = 0x7333333333333333;
integer * 10 = 0x47FFFFFFFFFFFFFFE, wraps to 0x7FFFFFFFFFFFFFFE
which is > integer.

It is unclear to me what effect an undetected overflow would actually
have from the user's viewpoint, so I'm not adding a NEWS entry.
This commit is contained in:
Kalle Olavi Niemitalo 2008-01-26 16:42:27 +02:00 committed by Kalle Olavi Niemitalo
parent f3bad399e2
commit a25fd18e56
1 changed files with 6 additions and 2 deletions
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8
src/protocol/bittorrent/bencoding.c
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@ -340,9 +340,13 @@ parse_bencoding_integer(struct scanner_token *token)
}
for (; pos < length && isdigit(string[pos]); pos++) {
if (integer > (off_t) integer * 10)
off_t newint = integer * 10 + string[pos] - '0';
/* Check for overflow. This assumes wraparound,
* even though C does not guarantee that. */
if (newint / 10 != integer)
return 0;
integer = (off_t) integer * 10 + string[pos] - '0';
integer = newint;
}
if (sign == -1)