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authorLinus Torvalds <torvalds@linux-foundation.org>2009-06-18 00:22:27 (GMT)
committerJunio C Hamano <gitster@pobox.com>2009-06-18 16:22:46 (GMT)
commit48fb7deb5bbd87933e7d314b73d7c1b52667f80f (patch)
treec2f64f6b71cb205b5422387b69d684ba0b733c09 /patch-delta.c
parent50a991ec46d57ffc4b7fbd0e8a13182dab3cd5de (diff)
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Fix big left-shifts of unsigned char
Shifting 'unsigned char' or 'unsigned short' left can result in sign extension errors, since the C integer promotion rules means that the unsigned char/short will get implicitly promoted to a signed 'int' due to the shift (or due to other operations). This normally doesn't matter, but if you shift things up sufficiently, it will now set the sign bit in 'int', and a subsequent cast to a bigger type (eg 'long' or 'unsigned long') will now sign-extend the value despite the original expression being unsigned. One example of this would be something like unsigned long size; unsigned char c; size += c << 24; where despite all the variables being unsigned, 'c << 24' ends up being a signed entity, and will get sign-extended when then doing the addition in an 'unsigned long' type. Since git uses 'unsigned char' pointers extensively, we actually have this bug in a couple of places. I may have missed some, but this is the result of looking at git grep '[^0-9 ][ ]*<<[ ][a-z]' -- '*.c' '*.h' git grep '<<[ ]*24' which catches at least the common byte cases (shifting variables by a variable amount, and shifting by 24 bits). I also grepped for just 'unsigned char' variables in general, and converted the ones that most obviously ended up getting implicitly cast immediately anyway (eg hash_name(), encode_85()). In addition to just avoiding 'unsigned char', this patch also tries to use a common idiom for the delta header size thing. We had three different variations on it: "& 0x7fUL" in one place (getting the sign extension right), and "& ~0x80" and "& 0x7f" in two other places (not getting it right). Apart from making them all just avoid using "unsigned char" at all, I also unified them to then use a simple "& 0x7f". I considered making a sparse extension which warns about doing implicit casts from unsigned types to signed types, but it gets rather complex very quickly, so this is just a hack. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'patch-delta.c')
-rw-r--r--patch-delta.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/patch-delta.c b/patch-delta.c
index ed9db81..ef748ce 100644
--- a/patch-delta.c
+++ b/patch-delta.c
@@ -44,7 +44,7 @@ void *patch_delta(const void *src_buf, unsigned long src_size,
if (cmd & 0x01) cp_off = *data++;
if (cmd & 0x02) cp_off |= (*data++ << 8);
if (cmd & 0x04) cp_off |= (*data++ << 16);
- if (cmd & 0x08) cp_off |= (*data++ << 24);
+ if (cmd & 0x08) cp_off |= ((unsigned) *data++ << 24);
if (cmd & 0x10) cp_size = *data++;
if (cmd & 0x20) cp_size |= (*data++ << 8);
if (cmd & 0x40) cp_size |= (*data++ << 16);