Date: Mon, 24 Oct 2011 10:02:46 +0530 From: Huzaifa Sidhpurwala <huzaifas@...hat.com> To: oss-security@...ts.openwall.com, Solar Designer <solar@...nwall.com> Subject: Re: hardlink(1) has buffer overflows, is unsafe on changing trees On 10/22/2011 08:51 AM, Solar Designer wrote: > > I investigated the non-crashing build further. No, adding more > directories did not cause a crash either. What happens is that lstat() > starts failing with ENAMETOOLONG shortly _after_ the overflow occurs. > This happens to limit the largest overflow size. If "dirs" is not yet > overwritten by this point (was not reached by the overflow), then the > program may proceed without crashing and without descending to deeper > directories (thus not overflowing the buffer even further). So > different builds may be affected to a different extent, depending on > relative placement of variables in .bss. The behavior may also vary by > kernel version, though (when lstat() starts to fail is a property of the > kernel, whereas NAMELEN in hardlink.c is fixed). I am able to make this > build crash with "*** buffer overflow detected ***" on the strcat(), > though, by carefully adjusting the directory name lengths (but that's > relatively uninteresting). > I think this is exactly what i hit, when testing on some Fedora/RHEL machines. Kernel defines the following: #define PATH_MAX 4096 /* # chars in a path name including nul */ And in the lstat implementation: if (dentry->d_name.len > NAME_MAX) return ERR_PTR(-ENAMETOOLONG); -- Huzaifa Sidhpurwala / Red Hat Security Response Team
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