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Remotely Compromising Android and iOS via a bug in Broadcom's WI-FI Chipsets

(blog.exodusintel.com)
387 points pedro84 | 4 comments | 26 Jul 17 19:51 UTC | HN request time: 0.001s | source
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Animats ◴[26 Jul 17 22:28 UTC] No.14860964[source]▶
C's lack of array size info strikes again:

    memcpy(current_wmm_ie, ie->data, ie->len);
where "ie" points to data obtained from the net.
replies(2): >>14861129 #>>14861284 #
revelation ◴[26 Jul 17 22:53 UTC] No.14861129[source]▶
C's lack of arrays strikes again. They are essentially syntactic sugar.
replies(1): >>14861235 #
frlnBorg ◴[26 Jul 17 23:15 UTC] No.14861235[source]▶
What do you mean by C not having arrays?
replies(5): >>14861254 #>>14861256 #>>14861257 #>>14861262 #>>14861281 #
JustSomeNobody ◴[26 Jul 17 23:18 UTC] No.14861254[source]▶
Probably referring to the fact that they are simply pointers into contiguous memory.
replies(1): >>14862377 #
1. astrange ◴[27 Jul 17 03:04 UTC] No.14862377[source]▶
C doesn't have "memory" in the standard. They're pointers into a contiguous object, but anything before a[-1] or after a[sizeof(a)-1] is undefined aka it actually doesn't exist.
replies(1): >>14885621 #
2. DiThi ◴[30 Jul 17 12:17 UTC] No.14885621[source]▶
`sizeof(a)` only gives the size of the array when the size is specified at compile time. Either you accept e.g. `int[16]` as a type, or you pass a pointer (for which `sizeof` just returns `sizeof(intptr_t)`)
replies(1): >>14887915 #
3. nemetroid ◴[30 Jul 17 21:26 UTC] No.14887915[source]▶
That's not quite right. Arrays always have a knowable length, and sizeof will give a correct result for variable length arrays as well.

However, arrays that are passed as arguments to functions decay into raw pointers, at which point you lose information about its length.

replies(1): >>14890975 #
4. DiThi ◴[31 Jul 17 11:31 UTC] No.14890975{3}[source]▶
> sizeof will give a correct result for variable length arrays as well.

In C99 with rather spotty support. And never with malloc and similar, which is how the vast majority of arrays are (and can be) created. And you can't return or store those dynamic arrays somewhere else without losing the size info, nor it can be declared static.

In other words, you're right but for very limited situations.