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From: Brooks Davis <brooks@one-eyed-alien.net>
To: musl@lists.openwall.com
Subject: [musl] out-of-bounds reads in strstr
Date: Tue, 8 Dec 2020 19:39:19 +0000	[thread overview]
Message-ID: <20201208193919.GA5522@spindle.one-eyed-alien.net> (raw)

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The strstr implementation contains the following snippet which results
in out-of-bounds reads in memchr (we detect them on CHERI because we
have byte-granularity bounds of small buffers):

	/* Fast estimate for MIN(l,63) */
	size_t grow = l | 63;
	const unsigned char *z2 = memchr(z, 0, grow);

The use of `|` means this is very much not an approximation of
`MIN(l,63)`.  What is actually intended here?  For CheriBSD (via FreeBSD)
I need a way to avoid out-of-bounds reads entirely (`MIN(l,63)` does seem
to work in simple system-level testing, but given the mismatch it's
unclear that's what was intended).

Thanks,
Brooks

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             reply	other threads:[~2020-12-08 19:42 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-08 19:39 Brooks Davis [this message]
2020-12-08 19:53 ` Rich Felker
2020-12-08 22:44   ` Brooks Davis
2020-12-08 22:57     ` Rich Felker
2020-12-09  6:54       ` Alexander Monakov
2020-12-09 16:37         ` Rich Felker
2020-12-24 22:26           ` Fangrui Song

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