Date: Wed, 10 Jun 2020 10:33:06 +0200 From: Szabolcs Nagy <nsz@...t70.net> To: Rich Felker <dalias@...c.org> Cc: musl@...ts.openwall.com Subject: Re: mallocng switchover - opportunity to test * Rich Felker <dalias@...c.org> [2020-06-09 20:58:26 -0400]: > On Tue, Jun 09, 2020 at 04:08:00PM -0400, Rich Felker wrote: > > On Tue, Jun 09, 2020 at 01:09:14PM +0200, Szabolcs Nagy wrote: > > > * Rich Felker <dalias@...c.org> [2020-06-08 23:50:10 -0400]: > > > > This produces a near-fully-integrated malloc, including support for > > > > reclaim_gaps donation from ldso. The only functionality missing, which > > > > I expect to flesh out before actual import, is handling of the case of > > > > incomplete malloc replacement by interposition (__malloc_replaced!=0). > > > > > > i would actually prefer if we didn't check for __malloc_replaced > > > in aligned alloc, because i think it does not provide significant > > > safety, but it prevents the simple RTLD_NEXT wrappers which are > > > commonly used for simple malloc debugging/tracing/etc (and while > > > unsafe in general depending on what libc api calls they make, > > > they likely work in practice). > > > > > > (the check does not provide safety because existing interposers > > > written for glibc likely work with musl too without issues: > > > the only problem is if musl uses aligned alloc somewhere where > > > glibc does not so an interposer may work on glibc without > > > interposing aligned alloc but not on musl. for newly written > > > interposers we just need to document the api contract.) > > > > I'm not sure about this, and how it interacts with our definition of > > posix_memalign and memalign in terms of aligned_alloc. > > What do you think of this proposal: > > Have ldso track both whether malloc was replaced and whether > aligned_alloc was replaced. If malloc was replaced but aligned_alloc > wasn't, aligned_alloc fails with ENOMEM. If both were replaced and our > internal aligned_alloc still gets called, assume some sort of wrapping > is going on and allow it to proceed. > > With mallocng, this is "safe" against misuse in the sense that it will > trap rather than corrupting memory if the contract is violated. sounds good to me.
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