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Date: Fri, 08 May 2015 11:46:21 +0200 From: Rasmus Villemoes <linux@...musvillemoes.dk> To: "Reese Faucette" <reesefaucette@...il.com> Cc: <linux-kernel@...r.kernel.org>, <alan@...rguk.ukuu.org.uk> Subject: Re: [PATCH] overflow check calculation in mm/mmap.c is incorrect linux-3.12.38 On Thu, Apr 30 2015, "Reese Faucette" <reesefaucette@...il.com> wrote: > When checking for overflow, the code in mm/mmap.c compares the first byte > *after* the end of mapped region to the start of the region instead of the > last byte of the mapped region. This prevents mapping a region which abuts > the end of physical space, as mmap() incorrectly rejects the region with > -EOVERFLOW, because pgoff + (len >> PAGE_SHIFT) will be 0, which is < > pgoff. Note this comment elsewhere in mmap.c: * We don't check here for the merged mmap wrapping around the end of pagecache * indices (16TB on ia32) because do_mmap_pgoff() does not permit mmap's which * wrap, nor mmaps which cover the final page at index -1UL. So it seems to be by design. But I'm also a little confused, since pgoff should be in units of pages (so a 20 bit number on 32bit), and I can't see how adding another 20 bit number could ever make that overflow. Unless of course some magic power ensures that pgoffs in the high half get sign-extended. Rasmus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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